Numerical modeling of thermal behavior and structural optimization of a-Si:H solar cells at high temperatures

Abstract

A large amount of solar energy is collected in tropical zones of the earth, where the temperature of photo-voltaic (PV) modules can exceed to more than $$70\,^{\circ }\text {C}$$70źC. At such high temperatures, the performance of most solar cells is greatly degraded, since the performance parameters of the cells are mainly decreasing functions of temperature. Despite the high importance of solar energy conversion in hot places, little attention has been paid to the investigation of high-temperature effects on the conversion efficiency of the cells. In this paper, the performance of a wide selection of solar cells of different structures made from different materials is analyzed at high temperatures in the range of 50---75 $$^{\circ }\text {C}$$źC, which is different from the standard test condition usually used in the assessment of solar cells. An accurate model for thermal behavior of the cell is suggested, in which almost all important parameters affecting each layer on the cell's thermal behavior are included, such as mobility, thermal velocity of carriers, bandgap, Urbach energy of band tails, electron affinity, relative permittivity, and effective density of states in the valence and conduction bands. The effects of possible arrangements of different layers and their materials and structural parameters, as well as light-induced defects and sunlight intensity, are also studied in the analysis. A relation is proposed between the optimal thickness of the absorber layer and the working temperature. Finally, an optimal structure of the solar cell at high temperatures is suggested.