A New Solar Cell


I must confess to being a novice in the areas of solar energy and photovoltaic diodes (PVDs , solar cells) , the devices that convert light into electricity . I have read only one book about these subjects : the broadbased overview , suitable for the layman , by Palz (the references are listed at the end of this web page . Underlined blue hyperlinks can be clicked when online to download the PDF or HTML file , which will open in a new window) . It seems to me that solar energy has for decades remained a dream of the future , with researchers being unable to exceed the roughly 30% or so efficiency level achieved by conventional PVDs , the “best” of them apparently still the costly gallium arsenide diode . Despite considerable , and ongoing , research and development , solar energy conversion remains uncompetitive with other major electricity production technologies .

I wonder if the fundamental problem with conventional PVDs is that they are based on semiconductors , which are all poor electrical conductors . As I understand it , conventional wisdom says that PVDs can’t be made from metals . Perhaps not from metallurgical metals , but how about from other types of metallic solids based on compounds , rather than elements ? In particular , I’ll proceed to outline the construction and functioning of a new type of PVD utilizing perovskite materials that may be metallic solids (and further down this web page , using pentacene derivatives) .

Most semiconductor materials these days are manufactured , now on a large scale , by the process of molecular beam epitaxy (MBE) , which in essence is “spray painting” atoms onto a substrate surface . An informative , readable account of MBE has been given by Amato . This has been developed into an extraordinarily precise method of atomic placement , such that semiconductor layers only a few atoms thick can be deposited onto the target substrate in the MBE apparatus , in a high vacuum . This sort of precision is required , for example , in the manufacture of light-emitting diodes (LEDs) , used in commercial electronics appliances such as the various sorts of laser reading and writing devices . So , I’m confident that the technology actually exists to implement my proposal for a new PVD , should basic research verify its performance and efficiency .

The two layers of perovskite comprising the light capturing and transforming zone of the diode would be the A0MX3 compound , such as  Ag0AlF3 (on the “outside” of the two layers , receiving the radiant energy) , and the corresponding doped mixed-valent composite on the “inside” of the bilayer , covering the substrate’s surface , in this case Ag(1-x)+AlxZn1-xF3 . Here is the situation with the two layers in the dark condition :

The “e-“ on the Age- atoms indicates the silvers’ 5s1 valence electrons , which could be located in a sigma XO connecting the silver atoms directly (that is , Ag0AlF3 could conceivably be a synthetic metal , with a high electrical conductivity) . The mixed-valent composite layer is coating the metal substrate . The doped composite could also be a synthetic metal , so the entire assembly envisaged here should have an excellent electrical conductivity , probably comparable to that of metallurgical metals . No electrical activity is anticipated in the diode when in the dark condition .When radiant energy such as sunlight falls on the diode , illuminating its outer Ag0AlF3 outer layer , some of the silvers’ 5s1 electrons in the sigma XO could be energetically promoted into a higher energy , physically larger frontier orbital , that extends into the doped composite layer . The photoexcited 5s electrons can fall into , and occupy the vacant 5s orbitals on the silver(I) cations in the composite layer :

When this photo-induced electron transfer occurs , the electrical charges become unbalanced in the two layers because of the underlying perovskite chemistry . This charge imbalance polarizes the two layers , with the outer one depleted of electrons gaining a positive charge , and the inner composite layer acquiring a negative charge as it receives the excited 5s electrons from the outer layer .

It should be emphasized that this electron transfer occurs only in the illuminated condition . As soon as the light source is removed and the diode is returned to its dark condition , the 5s electrons instantly flow back to the Ag0AlF3 outer layer to rebalance the assembly . Although quantum processes are usually credited with the photo-induced electron transfer – as in promotion of the 5s electrons to a higher energy , more voluminous frontier orbital – I wonder if we could look at the electron transfer process as occurring under the pressure of the radiant energy . We know that radiant energy does exert a vanishingly small , yet finite pressure on surfaces it falls on . This phenomenon has been the basis , for example , of the science fiction-like scheme for solar-powered vessels traveling in outer space between the planets , sailing like ships of the past on oceans , using the pressure of the sunlight on enormous light-gathering sails extending far out  beyond the spaceship . In the case of this new type of PVD , the light falling on the surface of the Ag0AlF3 could perhaps push under its pressure the 5s1 electrons in the readily deformable sigma XO metallic bond into the composite layer underneath . Actually , the metallic bond would be continuous throughout the assembly , and there would be no insulating interface between the two layers . The sunlight , or other radiant energy , would “push” the electron density from the outer to the inner layer , and in doing so would create the polarization between them .

This polarization would appear physically as a potential difference (p.d.) , or voltage , between the two layers . By placing electrodes strategically on or in the two surfaces , we should be able to tap this p.d. to do useful work for us . An external circuit connected to the electrodes will permit the excited 5s electrons in the composite layer , as long as the diode is still in the illuminated state , to travel back to the outer Ag0AlF3 layer , and as they do so , they can do useful work , such as running an electric motor or causing a lightbulb to shine . And so the cycle continues , the 5s electrons moving around through the diode’s layers and through the work circuit . The sunlight  or other radiant energy will have been converted into electrical energy .

The success of this scheme will depend on the photochemistry of the Ag0AlF3 / composite system . Will sunlight actually energize the 5s electrons , and promote them into the composite layer to join up with the Ag(I) cations ? Or alternately , will the sunlight be able to physically push under its pressure the 5s electrons through the metallic bond into the underlying composite layer ? However you visualize the system , its success will hinge on its photochemistry . Other related systems could also be investigated in this regard , such as the Tl0EuF3 / Tl(1-x)+EuxCd1-xF3 , in which I have predicted the additional interesting feature of redox resonance among its metal atom components .

We need not confine our search for new PVD materials to perovskites , either . The copper-based thiospinel system , for example , might also be looked at in this regard : Cu0Ti2S4 acting as the donor layer , and the doped composite Cu(1-x)+Al1-xTi1+xS4 forming the acceptor layer over the metal (or other) substrate . In general , the “electron rich” zerovalent compound would comprise the outer illuminated layer , while the “electron poor” (with “holes” in its XO , to receive the photoexcited electrons) composite , with its mixed-valent cations , would serve as the inner electron receiver . The creative solid state chemist could undoubtedly devise many more such candidate bilayer systems to be evaluated for their photochemical activity .

Update (added in mid-September , 2007) : in a related web page , "New Solar Cells from Mixed-Valent Metallic Compounds" , I discuss the possibility of single layer PVTs (photovoltaic transducers) made from the lower layer of mixed-valent compound . That is , the upper layer of zerovalent metallic compound may not be necessary . A brief review of mixed-valent compounds is provided , with an outline of the chemistry of possible preparations of new synthetic metal perovskites like that of the compound Ag(1-x)+AlxZn1-xF3 mentioned above .

The latter half of the twentieth century has rightly been called the “Silicon Age” (Sass) , from the revolutionary effect the transistor and its many descendants have had on our modern daily life . Perhaps , though – at least where solar electrical energy is concerned – we should look outside the “semiconductor box” for new solutions to unlocking this largely untapped bountiful energy supply . The new metallic solids described in this study may offer such a novel approach to the economic and widespread production and distribution of solar electricity .

The following section , describing a hypothetical organic molecular solar cell , was not in the ebook , but is presented as an annex to the discussion above .

The Pentacene PVD

The organic compound pentacene is a semiconductor and is being investigated for applications in electronics and solar electrical cells :

Pentacene derivatives are also being examined in these contexts . It might be possible to design and construct a novel type of organic molecular solar cell based on the principles discussed above for the inorganic metallic solids . Referring to the simplified , idealized sketch below , the pure , undoped pentacene compound would form the upper layer of the assembly , oriented toward the light source . Sandwiched underneath it would be the lower doped pentacene layer , which has "positive holes" in its pi XO (bond system) . The light radiation on the upper layer would photochemically excite some of the pi XO electrons in it , causing them to be "pushed down" into the lower layer , where they are temporarily lodged in the positive holes there . As a result , the upper layer with an electron deficit would become positively charged , and the lower layer with the excess (photoexcited) electrons would have a negative charge . The potential difference (p.d.) between the two layers should be measurable as the voltage generated by the incident radiation , solar or otherwise , on the upper pentacene surface :

For the doped pentacene compound (with the positive holes) in the drawing above I would suggest using the Wurster Blue derivative of the pentacene compound . Wurster Blues are tertiary aromatic amines , one of whose nitrogens has been converted into a radical cation aminium salt by a one-electron oxidizer . They have a deep sapphire blue colour , caused by the resonance throughout the pi MO of the molecule of the unpaired singlet electron , formally from the aminium nitrogen :

Note that the Wurster Blue molecule is identical in structure to its parent amine base , except that it has one less electron in its outer pi MO . Thus , the lower layer of Wurster Blue salt in the solar cell assembly should be able to provide the positive holes into which the photoexcited electrons from the upper layer can be "pushed" by the radiant energy (sunlight) .

Since Wurster Blues are prepared from tertiary aromatic amines (as in the original Wurster Blue perchlorate shown above) , it will be necessary to design and synthesize pentacene derivatives with this additional functionality . I believe that it would also be possible to derive Wurster Blues from aromatic ethers and sulfides (thioethers) , although I haven't done a literature search for these compounds . I'll outline proposed syntheses of new pentacene derivatives for photovoltaic diode research based on several amine , ether , and sulfide modifications of pentacene :

The amines , ethers , and sulfides have the peculiar structures shown above because their suggested syntheses are based on benzoquinone-hydroquinone chemistry . That is , the central "third" benzene ring is derived from benzoquinone , which can be readily reduced to its "hydrogenated form" of hydroquinone :

1,4-benzoquinone  + 2 H+  +  2 e-   ---------------->   hydroquinone ;  E0red  =  (0.6992  +  0.059 log [H+] ) V .

This half-reaction is the basis of the "Quinhydrone Electrode" , used in pH measurement in electrochemistry . Conversely , hydroquinone can be easily oxidized back to benzoquinone by a various oxidizing agents .

I don't have space in this web page for a review of benzoquinone-hydroquinone chemistry , as fascinating as it may be . In a nutshell , nucleophilic reagents add in an a,b manner to the double bond of benzoquinone . After the first equivalent of nucleophile has added to the substrate , the adduct undergoes a rapid tautomerization to the hydroquinone , since the reagent R-H has in effect reduced the benzoquinone . A second equivalent of nucleophile can add to the intermediate hydroquinone , but it must first be oxidized in situ by an oxidizer in the reaction mix back to the corresponding benzoquinone . It should be noted that the first equivalent of nucleophile adds to carbon 2 of the benzoquinone (by default) . It has been shown experimentally that the second equivalent of reagent always adds to carbon 5 of the regenerated quinone :

An excellent example of such a 2,5-bis-addition is the facile formation of the adduct of two equivalents of anthranilic acid to 1,4-benzoquinone , in which the researchers cleverly included sufficient oxidizer (sodium perchlorate) in the reaction mix to carry out two consecutive oxidations of the hydroquinones back to their corresponding benzoquinones :

The reactions outlined below involving the "5,12-diazapentacenes" are all modeled on this neat reaction of benzoquinone and anthranilic acid .

To start with , let's look at a possible route to 2,9-bis(dimethylamino)pentacene and its Wurster Blue salt . Phenylsodium will exchange its sodium atom with one of toluene's a-methyl hydrogens to produce benzene and benzylsodium . Similarly , this exchange reaction could be tried using the 4-dimethylamino analogue of toluene , N,N-dimethyl-p-toluidine . The toluidine carbanion is nucleophilic , and should readily add to benzoquinone :

Continuing , it should be possible to methylolate the hydroquinone bis-adduct with formaldehyde , joining the outer rings to the middle ring with methylene bridges (hydroquinone reacts readily with formaldehyde , like phenol) . Reduction of the bis-para-toluenesulfonylhydrazide by the Shapiro reaction (treatment with methyl- or n-butyl-lithium in ethyl ether) would provide the bis-alkene . Another similar sort of reduction of the bis-tosylhydrazide to the corresponding methylene compound could be accomplished with sodium borohydride . Finally , aromatization (dehydrogenation) of the deoxygenated intermediate to the pentacene derivative might be achieved using either the inexpensive sulfur , or palladium on charcoal , or even a combination of the two :

We note in the sketch above that if two water molecules could be removed from hydroquinone derivative 4 , we could obtain the desired pentacene compound 7 in a single step . Thionyl chloride and phosphorus oxychloride both react irreversibly with water and with hydroxyl groups :

SOCl2  +  2  H2O  ----------------->   SO2 (g)  +  2  HCl (g)

POCl3  +  1.5 H2O  --------------->   H3PO4    +  3  HCl (g)

There are examples in the literature in which the combination of thionyl chloride or phosphoryl chloride and pyridine will cause the dehydration of an alcohol to the corresponding alkene . It might be interesting to examine such a dehydration reaction with the hydroquinone derivative 4 :

In a bold venture , we might attempt a one-pot synthesis of the hydroquinone intermediate 4 directly from hydroquinone itself , reacting it first in a 2,5-bis-methylolation with formaldehyde and N,N-dimethylaniline . After the initial reaction is completed , two more equivalents of formaldehyde are added in the second step , and the pentacene rings are closed . In a second reaction , intermediate 4 would be dehydrated and aromatized , possibly with a reagent pair such as thionyl chloride in pyridine , as mentioned above :

Caution : Both the Aldrich Catalog Handbook of Fine Chemicals and the Merck Index state that the starting material N,N-dimethylaniline is very toxic , so researchers investigating the above reaction should be careful handling it and observe all safety precautions with it . N,N-dimethylaniline is a relatively inexpensive chemical , used primarily in the synthesis of dyes such as Crystal Violet . Of course , a simple , economical preparation of the pentacene derivatives is desirable , so that if they prove to be successful in solar cell applications , they will be readily available in bulk quantities to meet the market demand for them in actual energy production units .

Treatment of 2,9-bis(dimethylamino)pentacene with one equivalent of a suitable one-electron oxidizer in a polar solvent such as acetonitrile should produce the corresponding Wurster Blue salt :

I have indicated in the above sketch the use of a nitrosonium salt , such as the hexafluorophosphate , as the one-electron oxidizer . Nitrosonium cation is a powerful oxidizer :

NO+   +   e-      --------------->    NO (g)      E0red  =  1.45 V

Nitrosonium salts are stable , crystalline , commercially-available reagents . Antimony pentachloride has also been used as a one-electron oxidizer in the preparation of the interesting Wurster Blue , tris(4-bromophenyl)aminium hexachloroantimonate , according to the following stoichiometry :

2  [ = N : ]  +  3 SbCl5   ------------------>    2  [ = N .+ ]  SbCl6-   +  SbCl3

Antimony(V) is a much weaker oxidizer than nitrosonium cation :

Sb (V)   +   2e-     --------------->   Sb (III)        E0red =  0.8 V  approx.

Doping graphite with about 75% of its weight in antimony pentafluoride raised its electrical conductivity from approximately 25,000 ohm-1-cm-1 to around a million ohm-1-cm-1. This highly conductive graphite , first prepared at the nearby University of Sherbrooke in 1973 , still holds the world record for the material with the highest ambient electrical conductivity (silver , the most conductive metallurgical metal , is far behind at 629,000 ohm-1-cm-1) . Suffice it to say that antimony pentachloride and the nitrosonium salts should be strong enough one-electron oxidizers to generate the Wurster Blue salts of the pentacene derivatives discussed here .

If the phenylsodium technique and subsequent route outlined above proved to be successful , it might be adapted in the synthesis of the sulfur analogue 2,9-bis(methylthio)pentacene , starting with the inexpensive starting material p-thiocresol . Caution : all these sulfur compounds (except possibly the nonvolatile Wurster Blue salts) are real stinkers !

Synthesis of the 5,12-diazapentacene derivatives would all begin with the addition of two equivalents of the aromatic amine to benzoquinone , with in situ oxidation by an oxidizing agent such as sodium perchlorate or persulfate in the mix , as was illustrated above with the addition of anthranilic acid to benzoquinone . The remaining steps are similar to the scheme outlined above for 2,9-bis(dimethylamino)pentacene . For example , starting with the inexpensive aniline , the parent compound 5,12-diazapentacene might be prepared :

Similarly , by using N,N-dimethylamino-1,4-phenylenediamine as the starting material , the interesting new pentacene derivative , 2,9-bis(dimethylamino)-5,12-diazapentacene , and its Wurster Blue salt , might be synthesized :

The thioether derivative of diazapentacene , 2,9-bis(methylthio)-5,12-diazapentacene , could probably be prepared in much the same manner :

The starting aniline derivative , 4-(methylmercapto)aniline , is commercially available (eg. Aldrich) , but is rather expensive , so I have outlined a possible preparation of it from 1-chloro-4-nitrobenzene (Aldrich , much cheaper) . Normally it is difficult for nucleophiles to displace a halogen atom from unactivated aryl halides such as chlorobenzene . However , a strong electron-withdrawing group such as nitro , located ortho or (in this case) para to the halogen atom , activates it toward displacement by common nucleophiles (methylthiolate anion , in our example) . Reduction of the nitro group to amine can be accomplished in good yields by various reagents . I have indicated the powerful reducer lithium aluminum hydride (LAH) in tetrahydrofuran (THF) . A base metal in mineral acid , such as zinc dust or iron filings in hydrochloric or sulfuric acid solution , would be a cheaper and simpler reducing system . Note however that many transition metal cations , like iron , will strongly bond to organosulfur molecules , possibly complicating the preparation , which is why LAH/THF was recommended for the nitro reduction .

The condensation of two equivalents of a,a'-dichloro-o-xylene with one equivalent of 1,4-dimethoxybenzene in a Friedel-Crafts reaction should be a convenient route to the bis-ether derivative , 6,13-dimethoxypentacene :

It might also be possible to dope pentacene itself with antimony pentachloride or a nitrosonium salt , which would remove an electron from the outer pi electron cloud in the pentacene molecules to form the corresponding pentacenium radical cations :

However , the Wurster Blue salts of the pentacene derivatives are probably more chemically stable than this latter pentacenium radical carbocation .




An experimental solar cell might be fabricated from these organic molecules , using the principles described above for the perovskite systems . The outer layer receiving the sunlight (or other illumination) would consist of the pure , undoped pentacene or one of its derivatives . The inner layer would be made from a deposit of the corresponding Wurster Blue salt on a metal surface . If the system photochemistry is right , the sunlight will excite pi electrons from the outer layer into the inner layer , whose "positive holes" can accept them . This causes the outer illuminated layer to develop a positive charge , and the inner layer to generate an equivalent negative charge . The potential difference is the voltage produced in the cell between the two layers . This can be tapped to do immediate useful work as the photoexcited electrons in the inner layer move through the external work circuit to return to the positive outer layer . Or , the solar electricity generated can be stored in an energy reservoir :

In practical terms , a small glass microscope slide could serve as the substrate for the deposition of a thin film of the pure pentacene compound . It could be partially silvered at one end , like a mirror , using silver nitrate solution and a reducing agent to "plate" a strip of the glass surface with a silver mirror . This strip of silvered surface would be left at the end of the slide to receive an electrode contact . The film of pentacene or one of its derivatives could be deposited on the lower side by either the evaporation of crystals from a suitable solvent or - probably better - by the vacuum sublimation of very pure crystals of the compound onto the entire "under side" of the glass slide .

The corresponding Wurster Blue salt would be deposited somehow onto one side of a metal sheet , cut to the same size as the glass slide . The metal would have to be chemically inert toward the Wurster Blue compound . The glass slide / metal sheet sandwich would then be carefully assembled with the "chemical sides" in close contact . An electrode contact point would be made on the silvered strip on the end of the glass slide (positive) , and somewhere suitable on the lower side of the metal sheet (negative) . Exposure of the glass side of the assembly to sunlight or other illumination would then hopefully generate a detectable potential difference (p.d.) across the electrode contact points .

A similar-sized rectangle of fused quartz , chemically pure silica (for example , as used in fiber-optic cable) , or Vycor (96% silica , 4% boron oxide) , could be substituted for the glass microscope slide as the upper surface of the cell . These latter materials are transparent to most ultraviolet rays of the sun's spectrum , and so would permit more radiant energy to reach the pentacene layer below .

One possible problem with all these bilayer systems might be their gradual deterioration with prolonged exposure to light and heat , as the two layers slowly merge into one with atomic or molecular diffusion . This would result in a steady decline in their observed output voltage , faster in hot operating conditions such as in the blazing desert sun , and slower in cold environments , as in outer space , deployed on satellites and space probes . Obviously , weathering and aging of the bilayers , and general deterioration of the experimental cell under various field conditions , would have to be carefully studied and monitored by researchers .




If the pentacene derivatives proved to be successful in this proposed application to solar energy cells , they would have an advantage - despite the fact they are semiconductors - over the inorganic type of bilayer systems discussed in the first part of this report , in that they would be more economical to fabricate into large area solar energy collectors than the former PVDs . The organic compounds are potentially printable ; that is , they could be formulated into dye compositions , which can be printed onto suitable substrates using modern printing press technology (I have even heard of computer printers being used for this purpose) . The inorganic bilayer systems , on the other hand , must be "laid down" in an MBE (molecular beam epitaxy) apparatus , which is much more complicated , costly , and smaller-scale than printing organic layers .

On the other hand , the inorganic bilayer systems would consist of synthetic metals , which have electrical conductivities comparable to the common metallurgical metals . They should demonstrate a measurable bias in current flow , which is the hallmark of semiconductor transistors . The electron-rich "outer" layer with its filled orbitals and higher electron density would behave like the n-junction of a transistor , while the "inner" layer of doped compound with its partially-filled orbitals acting as "positive holes" and lower electron density would serve as the p-type junction . Since the bilayer systems have much higher electrical conductivities than semiconductors , their resistances would be correspondingly lower ; hence , their ohmic (heat) losses would be considerably less . Electrical devices like computers using them would run cooler than with the semiconductors . Electronic components such as printed circuits could be miniaturized even further , providing yet more power and memory .

The inorganic bilayer compounds would have a much higher density of atomic packing than the rather loose packing of the molecules in organic solids . They should therefore exhibit a greater energy density output in solar energy cells than organic semiconductors like the pentacenes . This is offset by their higher production costs , as mentioned . But the inorganic materials would have a potentially broader range of applications in electronics generally , with the possibility, I believe , of eventually displacing the silicon and germanium semiconductors in our present-day electronic devices .


References and Notes


this study : R.B. Steele , Exploring the Chemistry of Metallic Solids , including Superconductors . This web page is an extract (with minor editing) of pages 302-306 from the ebook (plus the added section on the use of new pentacene derivatives in solar cell research) .

W. Palz , Solar Electricity , An Economic Approach to Solar Energy , Butterworths , London , UK / UNESCO , Paris , France , 1978 .

uncompetitive : That solar electricity is still unattractive economically (compared to other forms of green energy) is graphically illustrated by two recent Canadian news stories . The first , which was reported on the Canadian Broadcasting Corporation online news service , CBC.ca , describes a solar power project being planned for construction near the southern Ontario town of Sarnia (near Detroit , MI) . The installation , to be completed by 2010 , will comprise over a million solar electrical panels , which should generate about 40 MW under optimum conditions . The news article states ,

“OptiSolar will be paid 42 cents per kilowatt-hour for the solar power generated , a much higher premium than the 11 cents a kilowatt-hour paid for wind power , another source of "green" energy in which the province has invested”.

See the article , “Ontario Approves Massive Solar Farm”, April 26 , 2007 , available online at : http://www.cbc.ca/technology/story/2007/04/26/tech-solar.html?ref=rss .

The second news story was from Quebec , whose monolithic electrical power corporation Hydro-Quebec was said to be in the market for new suppliers of wind energy for its grid : Robert Gibbens , “Hydro-Quebec Calls for Wind-Power Bids”, The Gazette (newspaper) , Montreal , Tuesday , May 1 , 2007 , p. B3 . Hydro-Quebec requires a 2000 MW wind power project , whose estimated cost is about $3 billion (Cdn) , to augment its present wind power capacity of 500 MW . Modern wind power generators are said to have an energy conversion efficiency of about 35% , roughly the same as the latest versions of multilayer gallium arsenide PVDs . Hydro-Quebec is offering to buy power from this future project at the rate of 5 cents per KWhr , half the price of wind power in Ontario ! The article can be read online at : http://www.wind-watch.org/news/2007/05/01/hydro-quebec-calls-for-wind-power-bids/

Clearly , present-day solar electricity simply can't succeed against such formidable competition as wind power . It makes much more sense to invest in wind power farms rather than solar power installations , especially in a northern country like Canada with its lower solar irradiation (see Matthias Loster's map of solar energy distribution , below) . A power giant and expert in green energy like Hydro-Quebec has made a clear choice in the matter . However , if we are to gradually phase out polluting fossil fuel energy production (eg. coal-fired generating plants elsewhere in Canada) , it will have to be replaced by all available green energy sources in a sort of "cocktail" of energy suppliers to the national electrical grid . Those energy sources must , and I'm sure will , include solar electricity . The development of new types of solar cells which have a much higher conversion efficiency , yet are economical to mass produce , will hasten the adoption of a widescale solar electricity contribution to the North American power grid .

The interest shown by Hydro-Quebec in wind power is proof that hydroelectric power development in Quebec is nearing an end . Another huge power project in central Quebec on the Eastmain River is still proceeding , but is probably the last of its kind . A combination of environmental concerns about river-damming , growing resistance to further power projects in the north by native people , and huge capital costs for new dams has effectively muted the enthusiasm of Hydro-Quebec for any future hydroelectric development . This would leave the door ajar for economical , high efficiency solar power installations in the province , assuming they can ever be devised and manufactured .

Actually , a logical first choice for both wind and solar power sites would be adjacent to the existing hydroelectric dams . The surplus power the wind and solar units produce could be used to pump water in the rivers below the dams back into the reservoirs to keep them "topped up". That would be a smart way of storing the potential energy of the wind and sun in a form (water storage) that could be readily converted into useful electrical energy upon demand , and could also be held in reserve against possible future periods of drought or low precipitation , which do occur from time to time .

In the sunnier United States relatively little hydroelectricity is produced , at least compared to Quebec , and almost no potential is left for developing new hydropower sources . By contrast , the potential for solar electric utilization in the United States , especially in its "Sunbelt" region , is vast , assuming a technological breakthrough to produce high efficiency solar cells . There is thus a much greater economic incentive to develop such new solar cells in the U.S. , than in Canada . Increased solar energy production must be accompanied by new technology to transport and store the green energy , so that it can be easily accessed and used by consumers .

Several general references about solar energy :

Wikipedia , “Organic Electronics”, http://en.wikipedia.org/wiki/Organic_electronics

Wikipedia , Photovoltaics, http://en.wikipedia.org/wiki/Photovoltaics

Wikipedia , “Solar Cells”, http://en.wikipedia.org/wiki/Solar_cells

Wikipedia , Solar Power, http://en.wikipedia.org/wiki/Solar_power . This is an excellent review article on the subject . The map below of the solar energy distribution on the Earth's surface was reproduced from this web page :

The author , Matthias Loster , comments ,

“Solar power systems installed in the areas defined by the dark disks could provide a little more than the world's current total primary energy demand (assuming a conversion efficiency of 8%) . That is , all energy currently consumed , including heat , electricity , fossil fuels , etc. , would be produced in the form of electricity by solar cells . The colors in the map show the local solar irradiance averaged over three years from 1991 to 1993 (24 hours a day) taking into account the cloud coverage available from weather satellites”.

The six areas defined by Loster are all in the "sunbelt" region of the Earth , in empty desert regions . Note that mid-latitude , northern and southern sections of the world are less suitable for solar electrical production . Thus , a country like Canada would likely be unable to produce all of its energy requirements , as 100% green energy , from solar electricity . It would have to be supplemented by additional sources of green energy , primarily hydroelectricity , with additional wind energy , and small amounts of tidal energy (eg. Bay of Fundy , NB and NS) .

The Wikipedia article on solar power states that the total amount of solar power received over the Earth's surface is 89 petawatts (89,000 terawatts) . Total human power consumption at any given moment was estimated to be a mere 15 terawatts . Loster's proposed six solar electricity production sites , sited in the above map , would produce a total of 18 terawatts , more than enough to satisfy humanity's needs . And that's at a rather conservative 8% conversion efficiency level . Imagine the possibilities that would open up to us if the new PVDs described in this essay had a conversion efficiency of , say 50% , or even 80% . Assuming co-developing technologies to efficiently transmit and store the generated solar electricity for use in off-peak hours (at night , cloudy days , etc.) , and for mobile applications (transportation) , human societies everywhere even in the Third World , with assistance from the First could gradually phase out the use of polluting hydrocarbon energy sources (coal , oil , natural gas) , reserving these non-renewable resources for their proper application as chemical feedstocks for future generations .

My thanks to Matthias Loster for implied permission to reproduce his solar power map on this web page .

perovskites :

R.M. Hazen , “Perovskites”, Scientific American 258 (6) , pp. 74-81 (June , 1988) .

Michael W. Davidson , The Perovskite Collection , at http://micro.magnet.fsu.edu/micro/gallery/perovskite/perovskite.html

WolfWikis , Perovskite, at http://wikis.lib.ncsu.edu/index.php/Perovskite

Perovskites have a rather simple crystal structure consisting of "supercube" cages of an MX3 compound , where M is a smaller metal cation , and X is an anion . In the center of each cubic cage is a large cation (or zerovalent atom) , A , giving perovskites their simple empirical formula , AMX3 :

molecular beam epitaxy :

Wikipedia , “Molecular Beam Epitaxy”, http://en.wikipedia.org/wiki/Molecular_beam_epitaxy

Alex Anselm , An Introduction to MBE Growth , on the web page ,


I. Amato , Stuff , The Materials the World is Made Of , Avon Books , New York , 1997 ; see especially pp. 119-125 for a description of the molecular beam epitaxy (MBE) technique , including a photograph of the industrial apparatus used for it (Figure 21 , p. 125) .

Molecular beam epitaxy is only one of a number of chemical vapour deposition (CVD) methods , used to deposit thin films of atoms on surfaces . A brief review of these techniques is provided by U. Schubert and N. Hüsing , Synthesis of Inorganic Materials , Wiley-VCH , Weinheim , Germany , 2000 ; pp. 71-112 , especially Table 3-2 , p. 84 ; MBE , p. 88 .

thiospinel : J. Padiou , D. Bideau , and J.P. Troadec , “Magnetic and Electrical Properties of Quaternary Thiospinels”, Chem. Abs. 92 , 225778j (1980) . Original article , which I haven’t been able to obtain :  J. Solid State Chem. 31 (3) , pp. 401-405 (1980) .

S.L. Sass , The Substance of Civilization , Materials and Human History from the Stone Age to the Age of Silicon , Arcade Publishing , New York , 1998 ; see Ch. 15 , “The Age of Silicon”, pp. 265-276 .

pentacene : Fabio Pichierri , Pentacene, Molecule of the Month website (University of Bristol , UK) , at : http://www.chm.bris.ac.uk/motm/pentacene/pentacene.htm .

Wikipedia , Pentacene : http://en.wikipedia.org/wiki/Pentacene

IBM Research , The Pentacene Project : http://www.research.ibm.com/leem/pentacene.html

H.W. Sands Corporation (supplier of pentacene) : http://www.hwsands.com/productlists/pentacene/pentacene.htm

Science Daily , Efficiently Organic : Researchers Use Pentacene To Develop Next-generation Solar Power : http://www.sciencedaily.com/releases/2004/12/041220005834.htm .

Pentacene derivatives : for example , see the web page , “Control of Pentacene's Solid-state Order”, http://www.chem.uky.edu/research/anthony/pentacene.html , by Prof. John Anthony (University of Kentucky , U.S.A.) .

Wurster Blue : for example , see the discussion and video demonstration of the formation of a Wurster Blue compound in solution , from Peter Keusch's web page , Wurster's Blue, at http://www.uni-regensburg.de/Fakultaeten/nat_Fak_IV/Organische_Chemie/Didaktik/Keusch/D-Wurster-e.htm

Quinhydrone : Peter Keusch , Formation of Quinhydrone, discussion , photos , and video : http://www.uni-regensburg.de/Fakultaeten/nat_Fak_IV/Organische_Chemie/Didaktik/Keusch/p15_chinhydr-e.htm

Shapiro : R.H. Shapiro , Alkenes from Tosyl Hydrazones, Ch. 3 , pp. 405-507 in Organic Reactions 23 , W.G. Dauben (ed.) , John Wiley , New York , 1976 . A practical example of the Shapiro reaction : R.H. Shapiro and J.H. Duncan , 2-Bornene, Org. Synth. Coll. Vol. 6 , p. 172 (1988) . Download this article (PDF , 150 KB) at no charge from the Organic Syntheses website at : http://www.orgsyn.org/orgsyn/pdfs/CV6P0172.pdf . Wikipedia : http://en.wikipedia.org/wiki/Shapiro_reaction . Shapiro's method is a modern variation of the older (1952) , somewhat similar Bamford-Stevens reaction (Wikipedia : http://en.wikipedia.org/wiki/Bamford-Stevens_reaction) .

sodium borohydride : L. Caglioti and P. Grasselli , A New Method for the Reduction of Aldehydes and Ketones to CH2 under Mild Conditions”, Chem. Ind. 1964 (2) , p. 153 ; A.N. deBelder and H. Weigel , “Synthesis of Deoxy-compounds from Carbohydrate Toluene-p-sulphonylhydrazones”, Chem. Ind. 1964 (40) , p. 1689 .

sulfur : see the mini-reviews of the reagents cited in L.F. Fieser and M. Fieser , Reagents for Organic Synthesis , vol. 1 , John Wiley , New York , 1967 : palladium on charcoal , pp. 779-780 ; sulfur , pp. 1118-1120 . Selenium is said to be superior to sulfur for aromatization (pp. 990-992) , but is much more expensive than it . Two preparations in Organic Syntheses involving dehydrogenation with sulfur : E.B. Hershberg and L.F. Fieser , “1,2-Napthalic Anhydride”, Org. Synth. Coll. Vol. 2 , p. 423 (1943) at http://www.orgsyn.org/orgsyn/pdfs/CV2P0423.pdf (PDF , 117 KB) ; R. Weiss , “1-Phenylnaphthalene”, Org. Synth. Coll. Vol. 3 , p. 729 (1955) at http://www.orgsyn.org/orgsyn/pdfs/CV3P0729.pdf (PDF , 137 KB) .

methylolation : I have discussed methylolation reactions in another web page , Polynapthalene . An interesting example of such a reaction that might be relevant to the proposed condensation of hydroquinone with N,N-dimethylaniline and formaldehyde is the formation of a-aminoethers and sulfides from the corresponding alcohols (RO–H) and thiols with formaldehyde and secondary amines :

RO–H   +  HCHO  +  H–N(Et)2  ----------------->  RO–CH2–N(Et)2  +  H2O

C.M. McLeod and G.M. Robinson , “Pseudo-bases . III Dialkylaminomethyl Alkyl Ethers and Sulfides”, J. Chem. Soc. 119 , pp. 1470-1476 (1921) ; T.D. Stewart and W.E. Bradley , “The Mechanism of Hydrolysis of Dialkylaminoethyl Ethers”, J. Amer. Chem. Soc. 54 (11) , pp. 4172-4183 (1932) .

These reactions are notable because they are carried out under neutral or basic conditions (indeed , the products are hydrolyzed in acid solution) . Under acidic conditions , the dimethylamino group will become dimethylammonium , which will deactivate the N,N-dimethylaniline ring to the methylolation . The following is an excellent example of the 2,5-bis-methylolation of hydroquinone :

N,N-dimethylaniline : I have recently learned that N,N-dimethylaniline has indeed participated in a methylolation reaction with formaldehyde and sodium sulfanilde :

nitrosonium : W.J. Plieth , Nitrogen, Ch. 5 , pp. 321-479 in Encyclopedia of Electrochemistry of the Elements , Vol. 8 , A.J. Bard (ed.) , Marcel Dekker , New York , 1978 ; p. 325 .

Antimony pentachloride : J. Holmes and R. Pettit , “Hydride Ion Abstraction with Antimony Pentachloride”, J. Org. Chem. 28 (6) , pp. 1695-1696 (1963) .

graphite : J.-M. Lalancette and J. Lafontaine , “Intercalation of Antimony Pentafluoride in the Lattice of Graphite”, J.C.S. Chem. Comm. 1973 , p. 815 ; F.L. Vogel , “The Electrical Conductivity of Graphite Intercalated with Superacid Fluorides : Experiments with Antimony Pentafluoride”, J. Mater. Sci. 12 (5) , pp. 982-986 (1977) .

electron-withdrawing : J.D. Roberts and M.C. Caserio , Basic Principles of Organic Chemistry , W.A. Benjamin , New York , 1965 ; p. 844 . J. March , Advanced Organic Chemistry , Reactions , Mechanisms , and Structure , 4th edition , John Wiley , New York , 1992 ; pp. 649-651 .

Friedel-Crafts : C.C. Price , “The Alkylation of Aromatic Compounds by the Friedel-Crafts Method”, Organic Reactions , Vol. 3 , Ch. 1 , pp. 1-82 , R. Adams (ed.) , John Wiley , New York , 1946 ; Table XI , p. 71 ; G.A. Olah and D. Meidar , “Friedel-Crafts Reactions”, Kirk-Othmer Encyclopedia of Chemical Technology , Vol. 11 , pp. 251-268 , M. Grayson and D. Eckroth (eds.) , John Wiley , New York , 1980 ; C.A. Thomas , Anhydrous Aluminum Chloride in Organic Chemistry , Reinhold Publishing , New York , 1941 ; Wikipedia : “Friedel-Crafts reaction” at http://en.wikipedia.org/wiki/Friedel-Crafts_reaction .

silvered : depositing a smooth silver deposit on glass might be accomplished by the Tollen's test , which is used in analytical organic chemistry and biochemistry to test for reducing sugars , such as glucose . It is discussed in many organic chemistry laboratory textbooks , and in Web articles . A description of the Tollen's Test (including the recipe of the required chemicals) , with an accompanying video (Real Player required) , is provided by Peter Keusch on his web page , Tollen's Reaction Silver Mirror Test, at http://www.uni-regensburg.de/Fakultaeten/nat_Fak_IV/Organische_Chemie/Didaktik/Keusch/D-Tollens-e.htm

The silvering of the inside of a glass bottle , “Silver Mirror”, with a video of the procedure (Quicktime MOV , 1994 KB) , is given by the Division of Chemical Education , Purdue University , West Lafayette , IN , at http://chemed.chem.purdue.edu/demos/main_pages/12.1.html .



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