High performance thermal-treatment-free tandem polymer solar cells with high fill factors

Abstract

It is an effective way to enhance device performance of polymer solar cells (PSCs) by using a tandem structure that combines two or more solar cells. For tandem PSCs, the buffer layer plays an important role in determining the device performance. The most commonly used buffer layers, such as PEDOT:PSS, TiOx, and ZnO, need thermal treatments that are not beneficial for reducing the fabrication complexity and cost of tandem PSCs. It is necessary to develop tandem PSCs fabricated by a thermal-treatment-free process. In this paper, we report high performance thermal-treatment-free tandem PSCs by developing PFN as buffer layers for both subcells. A power conversion efficiency (PCE) of 10.50% and a high fill factor of 72.44% were achieved by stacking two identical PTB7:PC71BM subcells. When adopting a rear PTB7-Th:PC71BM subcell, the highest PCE of 10.79% was further obtained for the tandem devices. The thermal-treatment-free process is especially applicable to flexible devices, in which plastic substrates are usually used.