Regensburg 2004 – scientific programme
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HL: Halbleiterphysik
HL 19: Symposium 50 Jahre Solarzelle
HL 19.3: Talk
Tuesday, March 9, 2004, 16:15–16:45, H15
Second and third generation photovoltaics: dreams and reality. — •J. H. Werner — Institut für Physikalische Elektronik, Universität Stuttgart
To more than 90 %, the present world market of solar cells is dominated by one material: crystalline silicon. Is has become common to term photovoltaics based on silicon wafers as No-dqfirst generationNo-dq photovoltaics. Research on No-dqsecond generationNo-dq photovoltaics, i.e. on thin film solar cells started as early as 1956 when the first Cu2S/CdS solar cell was prepared. Research on this type of cells was essentially given up around 1980 because 10 % efficiency have never been exceeded. At the same time, substantial research started on amorphous silicon, which now stands at 13 % (stable) efficiency compared to almost 25 % for the world best cells from crystalline silicon. Thus, early second generation photovoltaics did not fulfil the dreams of a cheap, highly efficient thin film technology. Nowadays, two other materials second generation are going into the production of commercial modules: CdTe and Cu(In,Ga)Se2. This presentation gives a critical assessment of these two materials which are highly interesting for research but as commercial products may suffer either from their toxicity or from their polycrystallinity. In particular, the inherent structural inhomogeneity of the polycrystalline films results in an electronic inhomogeneity which limits the performance of cells and modules in several ways. As a consequence, even in the case of second generation photovoltaics, the material of choice probably will be again crystalline silicon. Only photovoltaic materials which either supplement crystalline silicon or lead to new principles for the conversion of solar radiation into electricity seem to be interesting for innovative research. From this point of view, research on No-dqthirdNo-dq generation photovoltaics, i.e. solar cells with potential efficiencies above the classic Shockley/Queisser limit of 30 %, including recent publications on ZnMnTe, will be critically discussed.