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

摘要

Cd_2SnO_4/CdS/CdTe/Cu_xTe/Au structure solar cells were made in samples of 20 × 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 °C ≤ T_a ≤ 260 °C) were studied. The best results were obtained for the lowest P_W, increasing the average efficiency from 6.9% to 9.8% as T_a 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 activation's optimal conditions were determined, the highest efficiency was 11.3% with an RTA single treatment. The improvement is attributed to the formation of Cu_(1.85)Te phase. It is shown that this kind of thermal treatment on Cu_xTe/Au back-contact of the cells can be employed to obtain higher area solar cells.