Temperature and doping level dependence of solar cell performance including excitons

Abstract

Recent papers have indicated that the excitonic population in silicon can approach that of minority carriers and make their presence felt even at room and higher temperatures in generation–recombination processes and solar energy conversion. This paper presents an investigation of temperature and doping-level dependence of silicon solar cell perfomance for doping levels from 10 16 to 10 18 cm −3 and temperature interval 100–500 K. Our investigation was been performed using the three-particle theory developed by R.Corkish, D.S.-P.Chan, and M.A.Green (J. Appl. Phys. 79 (1996) 195). We have found that dissociation lifetime and diffusion length of excitons are 3–6 orders of magnitude less than that of free carriers. Inclusion of excitons results in a significant increase of dark current, decrease of short-circuit current, open-circuit voltage, fill factor, and efficiency. The results obtained, taking into account the effect of excitons, are in good agreement with experimental data. We have found accurate and simplified expressions for the dark saturation current and short-circuit current. Approximate value of the upper limit of photogeneration intensity of excitons φ ex is found that is at least eight times less than that of free carriers φ, i.e., φ ex⩽ φ. An optimal doping-level range of silicon solar cell base region was found that is less than 10 17 cm −3, and agrees with experimental data. The work includes a suggestion for experimental methods to confirm exciton involvement in photocurrent transport in silicon solar cells.