Coevaporated Cd_(1-x)Mg_xTe thin films for CdTe solar cells

摘要

Substantial improvement of the open-circuit voltage of thin film solar cells has been investigated by applying an electron reflector strategy. Cd1-xMgxTe has a strong potential as an electron reflector to keep minority carriers away from the CdTe back surface to reduce the back surface recombination. In this paper, SCAPS simulations were first used to investigate device performance for CdTe solar cells with the electron reflector layers. The theoretical results indicate that the similar to 0.4 eV electron barrier height for CdTe solar cells with Cd1-xMgxTe (E-g similar to 1.85 eV) is sufficient to decrease the back surface recombination and improve device performance, especially the open-circuit voltage. Thus the variation of energy gap of the Cd1-xMgxTe thin films prepared by coevaporation as a function of x was investigated from the transmittance spectra. Then Cd1-xMgxTe (x similar to 0.3) thin films were used as the electron reflectors for the CdTe thin film solar cells. It is found that CdTe solar cells with Cd1-xMgxTe yielded open-circuit voltage of 804 mV and fill factor more than 70% after an 425 degrees C anneal, which is higher than those without Cd1-xMgxTe. The electron reflector in CdTe solar cells can effectively reduce the carrier surface recombination, thereby resulting in the increase of the fill factor and the open-circuit voltage. (C) 2019 Elsevier Ltd. All rights reserved.