Organic solar cells utilize an energy-level offset to generate free charge carriers. Although a very small energy-level offset increases the open-circuit voltage, it remains unclear how exactly charge generation is affected. Here we investigate organic solar cell blends with highest occupied molecular orbital energy-level offsets (∆E_HOMO) between the donor and acceptor that range from 0 to 300 meV. We demonstrate that exciton quenching at a negligible ∆E_HOMO takes place on timescales that approach the exciton lifetime of the pristine materials, which drastically limits the external quantum efficiency. We quantitatively describe this finding via the Boltzmann stationary-state equilibrium between charge-transfer states and excitons and further reveal a long exciton lifetime to be decisive in maintaining an efficient charge generation at a negligible ∆E_HOMO. Moreover, the Boltzmann equilibrium quantitatively describes the major reduction in non-radiative voltage losses at a very small ∆E_HOMO. Ultimately, highly luminescent near-infrared emitters with very long exciton lifetimes are suggested to enable highly efficient organic solar cells.

有机太阳能电池利用能级偏移来生成自由电荷载流子。尽管很小的能级偏移会增加开路电压，但仍不清楚如何精确影响电荷产生。在这里，我们研究了在供体和受体之间具有最高占据分子轨道能级偏移（∆ E _HOMO）的有机太阳能电池混合物，其范围从0到300 meV。我们证明了激子猝灭在可忽略的∆ E _HOMO上发生在接近原始材料的激子寿命的时间尺度上，这极大地限制了外部量子效率。我们通过电荷转移态与激子之间的玻尔兹曼稳态平衡定量地描述了这一发现，并进一步揭示了激子寿命长，对于在可忽略的∆ E _HOMO下保持有效的电荷产生起决定性作用。此外，玻尔兹曼平衡定量地描述了在非常小的∆ E _HOMO下非辐射电压损失的大幅减少。最终，提出了具有非常长的激子寿命的高发光近红外发射器，以实现高效的有机太阳能电池。