The use of non-fullerene acceptors (NFAs) in organic solar cells has led to power conversion efficiencies as high as 18%¹. However, organic solar cells are still less efficient than inorganic solar cells, which typically have power conversion efficiencies of more than 20%². A key reason for this difference is that organic solar cells have low open-circuit voltages relative to their optical bandgaps³, owing to non-radiative recombination⁴. For organic solar cells to compete with inorganic solar cells in terms of efficiency, non-radiative loss pathways must be identified and suppressed. Here we show that in most organic solar cells that use NFAs, the majority of charge recombination under open-circuit conditions proceeds via the formation of non-emissive NFA triplet excitons; in the benchmark PM6:Y6 blend⁵, this fraction reaches 90%, reducing the open-circuit voltage by 60 mV. We prevent recombination via this non-radiative channel by engineering substantial hybridization between the NFA triplet excitons and the spin-triplet charge-transfer excitons. Modelling suggests that the rate of back charge transfer from spin-triplet charge-transfer excitons to molecular triplet excitons may be reduced by an order of magnitude, enabling re-dissociation of the spin-triplet charge-transfer exciton. We demonstrate NFA systems in which the formation of triplet excitons is suppressed. This work thus provides a design pathway for organic solar cells with power conversion efficiencies of 20% or more.

在有机太阳能电池中使用非富勒烯受体 (NFA) 已导致功率转换效率高达 18% ¹。然而，有机太阳能电池的效率仍然低于无机太阳能电池，无机太阳能电池的功率转换效率通常超过 20% ²。这种差异的一个关键原因是有机太阳能电池的开路电压相对于它们的光学带隙³较低，这是由于非辐射复合⁴. 为了使有机太阳能电池在效率方面与无机太阳能电池竞争，必须识别和抑制非辐射损失途径。在这里，我们表明在大多数使用 NFA 的有机太阳能电池中，开路条件下的大部分电荷复合是通过形成非发射 NFA 三重态激子进行的；在基准 PM6:Y6 混合^5中，这一比例达到 90%，开路电压降低了 60 mV。我们通过设计 NFA 三重态激子和自旋三重态电荷转移激子之间的大量杂交来防止通过这种非辐射通道的重组。建模表明，从自旋三重态电荷转移激子到分子三重态激子的反向电荷转移速率可能会降低一个数量级，从而使自旋三重态电荷转移激子能够重新解离。我们展示了 NFA 系统，其中抑制了三重态激子的形成。因此，这项工作为具有 20% 或更高功率转换效率的有机太阳能电池提供了设计途径。