Competition between recombination and extraction of free charges determines the fill factor of organic solar cells

作者：Davide Bartesaghi, Irene del Carmen Pérez, Juliane Kniepert, Steffen Roland, Mathieu Turbiez, Dieter Neher, L. Jan Anton Koster · 发表于：Nature Communications · 年份：2015 · DOI：10.1038/ncomms8083 · 被引用次数：635 · 研究领域：Organic Electronics and Photovoltaics、Perovskite Materials and Applications、Conducting polymers and applications

Among the parameters that characterize a solar cell and define its power-conversion efficiency, the fill factor is the least well understood, making targeted improvements difficult. Here we quantify the competition between charge extraction and recombination by using a single parameter θ, and we demonstrate that this parameter is directly related to the fill factor of many different bulk-heterojunction solar cells. Our finding is supported by experimental measurements on 15 different donor:acceptor combinations, as well as by drift-diffusion simulations of organic solar cells in which charge-carrier mobilities, recombination rate, light intensity, energy levels and active-layer thickness are all varied over wide ranges to reproduce typical experimental conditions. The results unify the fill factors of several very different donor:acceptor combinations and give insight into why fill factors change so much with thickness, light intensity and materials properties. To achieve fill factors larger than 0.8 requires further improvements in charge transport while reducing recombination.