Optimizing the Charge Carrier and Light Management of Nonfullerene Acceptors for Efficient Organic Solar Cells with Small Nonradiative Energy Losses
Yanan Shi, Junxiu Pan, Jianwei Yu, Jianqi Zhang, Feng Gao, Kun Lü, Zhixiang Wei
Abstract
The photovoltaic properties and energy losses of organic solar cells (OSCs) based on nonfullerene acceptors (NFAs) are highly dependent on their molecular structures and aggregation morphologies. Charge carrier and light managements are important to optimize NFA molecules. Herein, four NFAs with different alkyl substituents and end groups, named BTP‐C11‐N2F, BTP‐C9‐N2F, BTP‐C9‐IC4F, and BTP‐C9‐N4F, are designed and synthesized by side‐chain shortening, end‐acceptor π ‐extension, and fluorination. As a result, a favorable morphology is achieved in BTP‐C9‐N4F‐based OSCs by using typical high bandgap polymer PM6 as a donor, and this system obtains the highest power conversion efficiency of 17.0% with a short circuit current ( J sc ) of 26.3 mA cm −2 , an open circuit current ( V oc ) of 0.85 V, and a fill factor (FF) of 75.7%. In addition, its light ( J sc ) and charge carrier ( V oc × FF) managements relative to the Shockley–Queisser limit are also increased. Extending the conjugation of the end groups increased the energy levels of NFAs and enabled an E loss of 0.50 eV with a nonradiative recombination loss of as low as 0.20 eV in BTP‐C11‐N2F‐based OSCs. This work provides an efficient strategy to optimize the molecular structures of nonfullerene acceptors and further improve the properties of OSCs.