Abstract
Despite the progress in the engineering of structures to enhance photocurrent in thin film solar cells, there are few comprehensive studies which provide general and intuitive insight into the problem of light trapping. Also, lack of theoretical propositions which are consistent with fabrication is an issue to be improved. We investigate a real thin film solar cell with almost conformal layers grown on a 1D grating metallic back-reflector both experimentally and theoretically. Photocurrent increase is observed as an outcome of guided mode excitation in both theory and experiment by obtaining the external quantum efficiency of the cell for different angles of incidence and in both polarization directions. Finally, the effect of geometrical parameters on the short circuit current density of the device is investigated by considering different substrate shapes that are compatible with solar cell fabrication. Based on our simulations, among the investigated shapes, triangular gratings with a very sharp slope in one side, so called sawtooth gratings, are the most promising 1D gratings for optimal light trapping.
Highlights
Solar cells are and attractive route towards sustainable production of electricity; among the various technologies, thin film silicon is attractive because of low material usage and the availability of advanced manufacturing technology
We investigate a real thin film solar cell with almost conformal layers grown on a 1D grating metallic backreflector both experimentally and theoretically
The investigated device is a single junction amorphous silicon solar cell grown on a onedimensional grating substrate that serves as textured back reflector and is made using the nanoimprint technique described in [26]
Summary
Solar cells are and attractive route towards sustainable production of electricity; among the various technologies, thin film silicon is attractive because of low material usage and the availability of advanced manufacturing technology. A fast and stable simulation tool for the prediction of light absorption in multi-layer stacks is of great benefit Full numerical methods such as finite difference time domain (FDTD) [11] and finite element method [12] can be used to obtain the electromagnetic field profile of a specific structure at a pre-defined frequency but they are not appropriate for an optimization due to unacceptable requirements of time or memory. Semi-analytical methods such as the differential method [13], the coordinate transformation method (C method) [14] and the rigorous coupled wave analysis (RCWA, called Fourier Modal Method, FMM) [15,16,17] are preferred Approximate solutions such as scalar scattering theory [18,19] can be used to get an initial insight but they rely on approximations that may not always be fulfilled, and they are normally not capable of handling polarization-dependent effects. We apply the modeling to explore the ideal structures like sinusoidal, triangular and binary gratings
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