CdS/CdTe solar cells by the screen-printing-sintering technique

Experimental approaches for the performance improvement of CdS/CdTe solar cells produced by the screen-printing and sintering technique are described. The bias voltage dependence of fill factor and performance degradation related to the lattice mismatch between CdS and CdTe are much improved by reducing the CdCl₂ residue in the sintered CdS film and optimizing the CdTe sintering condition, especially the sintering temperature and the heat-up rate. Electron-beam-induced current (EBIC) and transmission electron microscopy (TEM) observations of the CdS/CdTe interface revealed that these improvements are due to the increased minority carrier diffusion length in the CdTe active layer. The lattice mismatch is relaxed by forming two types of mixed-crystal layers between CdS and CdTe. As a result, the conversion efficiencies of 11.3% in 1.07-cm² and 6.2% in 1200-cm² total area (8.7% in active area) are obtained