An efficient analytical model for tandem solar cells

In this paper, a new analytical and computational methodology for modeling tandem solar cells is developed using the interfacial potential aspect. The presented model provides a correct and simple description of the multijunction solar cell behavior under illumination. In addition to its simplicity, the main advantage of the developed model with respect to previous ones resides on the inclusion of the effect of interfacial defects on the open circuit voltage deficit. The proposed model provides the possibility for optimizing input parameters associated with both bottom and top cells to achieve high efficiency values. The analytical results of a kesterite/kesterite tandem solar cell are compared with numerical ones, where a good agreement is obtained thus confirming the validity of the presented model. The impact of the absorbers thickness on the solar cell performance is investigated. Moreover, the effect of the Cu2ZnSn(SxSe1-x)4(CZTSSe) band-gap on the tandem solar cell efficiency is analyzed, where it is found that a high power efficiency value of 22.5% can be achieved by taking CZTSSe band-gap with 1.3 eV. Therefore, the developed analytical model is absolutely useful not only for designing high-efficiency tandem solar cells, but also for implementation in software device simulators, in order to accurately analyze and optimize multi-junction solar cells reliability and performance.