Photovoltaic Characteristics of GaAs Solar Cells with Selective Filters

Enhancing the photon recycling process in a solar cell can boost the open-circuit voltage (V-oc). In this work, we employ a selective filter realized by alternative TiO2 and SiO2 dielectric layers with different cutoff wavelengths as the front surface structures, and a distributed Bragg reflector (DBR) grown by epitaxy on the rear side of GaAs solar cells to form an optical cavity. The idea is to suppress the radiative recombination emission loss at the material bandgap toward the front and rear side by increasing photon-recycling via a cavity design with minimal auxiliary impact on light current. From our experiment, when cut-off wavelength was designed at 840nm, the V-oc of the cell increase by 1.1mV compared with the device without the selective filter. Moreover, we successfully developed an optical model that combines a rigorous couple wave analysis (RCWA) and photon recycling calculation NREL developed recently to quantify the V-oc enhancement from different optical design on GaAs solar cells. Based on theoretical optimizations of the experimental data, if we can optimize the back DBR reflector or using metal as the back mirror, we can obtain a large V-oc enhancement by 36.4mV using the selective filter with a cut-off wavelength of 840 nm. However, although we can use selective filter as top structure to improve the V-oc, the power conversion efficiency is still limited due to the implementation of selective filters has affected light absorption at the desired spectral range. Nevertheless, this concept of light management may be further improved by using angular filters in order to prevent the loss of light current while improving the V-oc and power conversion efficiency at the same time.