A parametric study of TiO2/CuInS2nanocomposite solar cells: how cell thickness, buffer layer thickness, and TiO2particle size affect performance

3D CuInS 2 /TiO 2 nanocomposite solar cell performance is strongly influenced by several structural factors, including cell thickness, buffer layer thickness, and the morphology of the TiO 2 nanoparticulate matrix. To delineate the effect of these structural factors on photovoltaic performance, a series of parametric studies are performed where a single structural parameter is varied (TiO 2 nanoparticulate matrix thickness, In 2 S 3 buffer layer thickness, or TiO 2 particle size) while all other fabrication conditions are held constant. The best overall performance (3.0% efficiency at AM 1.5) is achieved from a device with TiO 2 matrix thickness ≈200 nm, In 2 S 3 buffer layer thickness ≈60 nm, and TiO 2 nanoparticulate size = 300 nm. Notably, the film thickness in the best-performing cell (200 nm) is less than the TiO 2 particle size (300 nm), corresponding to a discontinuous nanoparticulate film. Thicker TiO 2 nanoparticulate films or smaller TiO 2 particles sizes lead to decreased performance due to increased charge transport resistance. However, the performance from a planar cell (where the TiO 2 nanoparticulate layer is not used) is inferior to the performance from the better-optimized 3D cells, indicating that some degree of nanostructuring improves performance. Device performance is also observed to depend strongly on In 2 S 3 buffer layer thickness, with optimal performance achieved for a buffer layer thickness of approximately 60 nm. The optimal buffer layer thickness is governed by two opposing factors: increasing the buffer layer thickness improves the interfacial characteristics (as measured by decreasing leakage conductance, G ) but also screens the incoming light and causes an increase in the charge transport resistance (as measured by the cell series resistance, R s ).