Surface sulfurization studies of thin film Cu(InGa)Se2 solar cells

Sulfurization of copper indium gallium diselenide (CIGS) thin films solar cell absorber has been attempted to enhance the open circuit voltage of the device by increasing the band gap of the absorber near the interface. The homogeneous co-evaporated Cu(InGa)Se2 thin film was used for sulfurization. The sulfurization was studied in hydrogen sulfide and mixture of hydrogen sulfide and hydrogen selenide gases with the inclusion of oxygen. The structural and compositional properties of the absorber layers were investigated by XRD, EDS and AES analysis. The device results were characterized using current–voltage (I–V) and quantum efficiency. Sulfurization in hydrogen sulfide gas forms a fully converted sulfide layer at the top of the absorber layer, which in turn forms a barrier for the current collection; the device results also support this observation. Sulfurization in mixture of hydrogen sulfide and hydrogen selenide gases forms a wide band gap Cu(InGa)(SeS)2 layer at the surface by partial replacement of Se by S. The device does not show an increase in open circuit voltage. This may be attributed to the diffusion of Ga away from the surface with the inclusion of sulfur at the surface, which counters the beneficial effect of sulfur at the surface.