A variety of CdS/CdTe heterojunction solar cells have been prepared by the vacuum evaporation of n-CdS films onto single-crystal p-CdTe substrates. Comparisons have been made between cells prepared using different substrate resistivities, substrate surface preparations, and CdS film resistivities. The mechanisms controlling the dark junction current, photocarrier collection, and photovoltaic properties with junction interface states present are modeled. A solar efficiency of 7.9% under 85 mW/cm2 of solar simulator illumination was measured on a cell with an indium-tin-oxide coating and a glycerol antireflection coating.

Optical-absorption coefficients for CdTe greater than 103 cm−1, calculated from the spectral-response curve of a CdS/CdTe heterojunction solar cell produced in our laboratory, are in agreement with recent optical measurements on thin films and bulk samples of CdTe. This technique allows high values of absorption coefficient to be measured in bulk samples, bypassing the problems associated with optical measurements in thin films. The high values of absorption coefficient determined for CdTe encourage its use as a thin-film solar-cell material.

Commercially produced, unencapsulated, Czochralski (CZ) silicon solar cells can lose 3%–4% (relative) of their initial efficiency after exposure to light, after minority-carrier injection during dark forward bias, or after thermal treatment at 100–400 °C. All three degradation methods reduce the minority-carrier diffusion length in the cell substrate. Under light, the decrease in efficiency is rapid (<30 min at 1 sun), but the cell power remains stable thereafter. The effect is completely reversible and the cell performance recovers in <12 h in the dark at room temperature. The various conditions under which CZ silicon cells degrade, and the reverse process, annealing, are characterized by spectral response and current–voltage (I–V) measurements. Iron impurities are a possible cause of this effect.

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