Optimizing Photovoltaic Charge Generation of Hybrid Heterojunction Core-Shell Silicon Nanowire Arrays: An FDTD Analysis

Development of highly efficient nanowire-based photovoltaic devices requires an accurate modeling of light scattering from interfaces and optical carrier generation inside the cell. A comprehensive study of optical absorption and carrier generation enables us to tap the full potential of nanowire arrays (NWAs). In this study, we have done a systematic study to optimize the core-shell structure of vertically aligned silicon nanowire (Si NW) arrays coated with PTB7:PCBM by means of finite difference time domain optical simulations to maximize the photon absorption. Initially, the core thickness of hybrid Si NWs has been optimized for the most efficient light absorption. The further improvement of light absorption has been studied by varying the coating thickness of low-band gap organic polymer PTB7:PCBM on Si NWAs. A delineative analysis shows that NWs with a 150 nm thick silicon core and 60 nm thick coating of PTB7:PCBM exhibit broad band absorption and the optimum ideal current density of about 34.95 mA/cm, which are larger than those of their planar counterpart with the same amount of absorbing material and also better than those previously reported for NWs. The basic principle and the physical process taking place during absorption and current generation have been also discussed. The optimization of the hybrid heterojunction Si NW arrays and understanding of their optical characteristics may contribute to the development of economical and highly efficient hybrid solar cells.