Structural and chemical transformations in SnS thin films used in chemically deposited photovoltaic cells

摘要

Chemically deposited SnS thin films possess p-type electrical conductivity. We report a photovoltaic structure: SnO_2:F-CdS-SnS-(CuS)-silver print, with V_(oc)>300 mV and J_(sc) up to 5 mA/cm~2 under 850 W/m~2 tungsten halogen illumination. Here, SnO_2:F is a commercial spray-CVD (Pilkington TEC-8) coating, and the rest deposited from different chemical baths: CdS (80 nm) at 333 K, SnS (450 nm) and CuS (80 nm) at 293-303 K. The structure may be heated in nitrogen at 573 K, before applying the silver print. The photovoltaic behavior of the structure varies with heating: V_(oc) ≈ 400 mV and J_(sc) < 1 mA/cm~2, when heated at 423 K in air, but V_(oc) decreases and J_(sc) increases when heated at higher temperatures. These photovoltaic structures have been found to be stable over a period extending over one year by now. The overall cost of materials, simplicity of the deposition process, and possibility of easily varying the parameters to improve the cell characteristics inspire further work. Here we report two different baths for the deposition of SnS thin films of about 500 nm by chemical deposition. There is a considerable difference in the nature of growth, crystalline structure and chemical stability of these films under air-heating at 623-823 K or while heating SnS-CuS layers, evidenced in XRF and grazing incidence angle XRD studies. Heating of SnS-CuS films results in the formation of SnS-Cu_xSnS_y 'Ail-chemically deposited photovoltaic structures' involving these materials are presented.