Beneficial effects of sodium on CuIn1-XGaXS2 thin film solar cells

Chalcopyrites are important contenders among solar cell technologies due to their direct band gaps and high absorption coefficients. Copper indium gallium sulfide, CuIn_1-xGa_xS₂ (CIGS2) thin films have been grown by sulfurization with copper rich compositions. However, the desired free carrier concentration range of 10¹⁶-10¹⁷/cm³ can be achieved fairly easily with copper deficient compositions avoiding the toxic etching process. Due to the unavailability of cuprous sulfide which acts as a fluxing agent in copper rich films and is responsible for better film morphology, it is difficult to produce device quality films in copper deficient compositions. The effects of sodium addition on the film microstructure and the device performance are being studied.