Effects of rapid thermal annealing as back contacts activation treatment on CdS/CdTe multi-contacted solar cells

Cd2SnO4/CdS/CdTe/CuxTe/Au structure solar cells were made in samples of 20 x 20 mm(2). Multiple metallic back-contacts were deposited on each sample by thermal evaporation. A series of rapid thermal annealing treatments (RTA) were performed on the cells, controlling work pressure (P-w) and temperature (T-a), to activate the interface of CdTe-back contact. Several combinations of pressure (746 mbar < P-w < 1112 mbar) and temperature (180 degrees C < T-a < 260 degrees C) were studied. The best results were obtained for the lowest Pw, increasing the average efficiency from 6.9% to 9.8% as Ta increased. All photovoltaic parameters (V-OC, J(SC), FF, R-S, and R-Sh) were enhanced with the RTA treatments along with the dispersion values. Once the thermal activa-tion's optimal conditions were determined, the highest efficiency was 11.3% with an RTA single treatment. The improvement is attributed to the formation of Cu1.85Te phase. It is shown that this kind of thermal treatment on CuxTe/Au back-contact of the cells can be employed to obtain higher area solar cells.