Tunable open-circuit voltage in ternary organic solar cells

Abstract

Recently, there are growing interests in ternary organic solar cells due to their expected broader absorption in comparison to their counterpart binary systems. It is found that open-circuit voltage in a ternary system can be largely tuned by varying the composition ratio of two donors or two acceptors integrated in. However, there is no detailed analysis for such an interesting observation. In this paper, we fabricated ternary solar cells with one p-type polymer as donor and two mixed n-type fullerenes as acceptor, and investigated the open-circuit voltage by varying the weight ratio of the two fullerenes. A three-diode model is developed to analyze the tunable behavior of open-circuit voltage displayed in our ternary system in terms of energy loss and dark current suppression. We also discussed the tunable open-circuit voltage based on electron and hole quasi-Fermi levels.