Simulation has been done using SCAPS-1D to examine the efficiency of CH 3 NH 3 SnI 3 -based solar cells including various HTM layers such as spiro-OMeTAD, Cu 2 O, and CuSCN. ZnO nanorod array has been considered as an ETM layer. Device parameters such as thickness of the CH 3 NH 3 SnI 3 layer, defect density of interfaces, density of states, and metal work function were studied. For optimum parameters of all three structures, efficiency of 20.21%, 20.23%, and 18.34% has been achieved for spiro-OMeTAD, Cu 2 O, and CuSCN, respectively. From the simulations, an alternative lead-free perovskite solar cell is introduced with the CH 3 NH 3 SnI 3 absorber layer, ZnO nanorod ETM layer, and Cu 2 O HTM layer.

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We present simulation and experimental results proving the feasibility of a novel concept to increase efficiency of CdTe based solar cells. In order to achieve $0.50/W price in CdTe based modules, higher efficiencies need to be attained. The high defect density due to lattice-mismatch between CdS and CdTe reduces lifetime, voltage, and efficiency of the cells. We propose the use of a graded composition structure and a patterned substrate to reduce defects, increase lifetime, and efficiency of the cells. Innovative simulations using high-fidelity molecular dynamics predict that defect-free films are possible if the CdTe film is graded with Zn and is constructed as nano-islands with sizes below 90 nm. Both graded structure and nano-islands reduce the lattice-mismatch stresses. Also, the graded composition creates a back surface field and an enhanced ohmic contact. We have attempted to grow ZnTe and CdTe films on CdS substrates using a template of micro and nano-islands. Selective growths on patterned substrates have shown fewer grain boundaries when the island size decreases below 300 nm. Also, larger grain sizes were obtained using a CdTe/ZnTe stack when compared to a single layer CdTe. The simulation and experimental results demonstrate for the first time the ability to use nanopatterned substrates to enhance uniformity in thin film solar cells.

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