CdS–CdTe solar cells were prepared by epitaxial growth of CdS on p·CdTe wafers, and properties of the cells were extensively studied. The cells have a junction structure of n·CdS–(n or i)·CdTe–p·CdTe. Formation of the (n or i) layer is due to diffusion of In into CdTe; the thickness of the layer was 0.5 µm in the most efficient cell. The best cell exhibited a solar conversion efficiency of 10.5% under illumination by sunlight (AM1.3, 68 mW/cm2), and 6.0% under illumination by a simulated sunlight (AMO). The high efficiency is attributed to the reduction in both the series resistance and surface recombination, which results from the presence of the heavily doped CdS layer on the wafer. The cell is not humidity sensitive and is stable in the forward bias test, These results suggest strongly that practically useful solar cells can be manufactured from this type of junction.

Thin film CdS/CdTe solar cells with an efficiency of 6.3 % have been prepared on a borosilicate glass substrate of 4s×4 cm2 by successively repeating screen printing and heating (sintering) of each paste of CdS, CdTe and C. The CdS paste consists of CdS, CdCl2, GaCl2 and propylene glycol (PG). The CdTe paste contains CdCl2 and PG, and the C paste contains PG and a small amount of acceptor impurity. During the heating of C paste, an n·CdS/p·CdTe heterojunction is formed. In the most efficient cell, the peak of electron voltaic effect exists within 1 µm of the CdTe side from the CdS/CdTe metallurgical boundary. The C electrode cell is more stable than the previous Cu2Te electrode cell for an accelerated life test. From 25 elemental cells with 4×4 cm2 substrate, a 1 watt module has tentatively been constructed with a module efficiency of 2.9 %.

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This paper describes the properties and the model of ceramic CdS photovoltaic cell made by treating CdS ceramic plate electrochemically in copper ion solution. The compositions and structures were analysed by means of X-ray Ginuie Camera and X-ray microanalyser. It was found that Cu2-x S (0≦x≦0.2) is formed along grain boundaries over a range of a several ten microns of the surface layer, and that the photovoltaic junctions exist at grain boundaries in this surface layer. From examinations of the voltage dependence of the barrier capacitance, the junctions could be classified into step junction, graded junction and Mott barrier, according to the prepared method. The spectral response measurement indicates that the origin of the photo-emf of the Mott barrier is mostly impurity photovoltaic effect.

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