POLYCRYSTALLINE THIN-FILM SOLAR-CELLS - PRESENT STATUS AND FUTURE POTENTIAL

Polycrystalline thin film solar cells on copper indium diselenide (Cul nSe(2)) and its alloys and cadmium telluride (CdTe) appear to be the m ost promising candidates for large-scale application of photovoltaic e nergy conversion because they have shown laboratory-efficiences in exc ess of 15%. Heterojunction devices with n-type cadmium sulfide (CdS) f ilms show very low minority carrier recombination at the absorber grai n boundaries and at the metallurgical interface, which results in high quantum efficiences. Open circuit voltages of these devices are relat ively low owing to the recombination in the space charge region in the absorber. Further improvements in efficiency can be achieved by reduc ing the recombination current, especially in devices based on CulnSe(2 ) and its alloys. Low-cost manufacturing of modules requires better re solution of a number of other technical issues. For modules based on C ulnSe(2) and its alloys, the role of Na and higher deposition rates on device performance need to be better understood. In addition, replaci ng the chemical bath deposition method for CdS him deposition with an equally effective, but more environmentally acceptable process is need ed. For modules based on CdTe, more fundamental understanding of the e ffect of chloride/oxygen treatment and the development of more reprodu cible and manufacturable CdTe contacting schemes are necessary.