Numerical analysis of bifacial indoor photovoltaic devices based on chalcogenide, kesterite and II-VI compounds

Abstract

In this thesis, we numerically investigate the performance of bifacial photovoltaic devices under practical combinations and incident angles of a solar and cool white LED source for three separate types of absorber materials: chalcogenide, kesterite and II-VI compounds. To represent each of these material groups, CuInGaSe2 (CIGS), CuZnSn(S,Se)4 (CZTSSe) and CdTe were chosen. By numerically solving Poisson’s equation and continuity equation under optical generation-recombination conditions and applying Finite Difference Time Domain analysis techniques, the monofacial performance of the three BPV devices were evaluated under an experimentally validated theoretical model. The monofacialparemeters were then used to calculate the bifacial performance characteristics of the three devices for normal incidence of solar and white LED light source. Out of all the lighting scenarios, front LED and rear solar illumination yielded the best effective bifacial efficiencies of 25.37% for the CIGS device and 8.54% for CZTSSe one, respectively, while the CdTe cell showed its highest efficiencies of

11.73% for white LED illumination in both front and back surface. Although CZTSSe and CdTe bifacial efficiencies were less than their monofacial counterparts, the credit of these bifacial devices lies in their highly increased short current densities, and unchanged open circuit voltages. The short circuit current densities for the best case scenarios were 68.98 mA/cm2, 43.09

mA/cm2 and 41.94 mA/cm2. The superior dominance of CIGS with regards to bifacial performance were traced back to the spectra dependent carrier generation recombination dynamics of the n-p heterojunction. Next, the oblique incidence performance characteristics of the three devices were studied for a realistic setup of 45° front LED incidence and varying 0° to 60° incidence of rear solar irradiance. While being relatively stable for the whole range of incident angles, the CIGS and CdTe device show a V shaped performance curve centered around 20°, providing highest bifacial efficiencies of 26.43% and 12.17% for the CIGS and CdTe, respectively. The CZTSSe device shows a downward trend with increasing rear incident angles. This thesis provides guidelines for selecting appropriate absorber materials suitable for operation under any possible lighting condition and incident angle, both indoor and outdoor.