Modeling polycrystalline effects on the device characteristics of cdte based solar cells

There are mainly three different types of losses that accounts for the decrease in the efficiency of polycrystalline CdTe solar cells namely: (1) optical losses resulting from the interface reflections and absorption from the window and buffer layers in superstrate configuration; (2) recombination losses due to the interface between adjacent layers and also at grain boundaries; and (3) electrical losses due to the device series and shunt resistances. Over the years researchers have mostly studied the nature of the optical and electrical losses in single crystalline cells and have put forward various theoretical models to accurately explain their effect on various performance parameters. However the problem gets much complicated for polycrystalline materials as grain size effects can significantly affect these performance parameters such as short circuit current, open circuit voltage and fill factor. In this work we have studied these polycrystalline effects in depth and have presented a comparative analysis using minority carrier lifetime based model to accurately formulate micron scale grain size effects in CdTe based solar cells.