Energy loss (E loss) consisting of radiative recombination loss (ΔE 1 and ΔE 2) and nonradiative recombination loss (ΔE 3) is considered as an important factor for organic solar cells (OSCs). Herein, two N-functionalized asymmetrical small molecule acceptors (SMAs), namely N7IT and N8IT are designed and synthesized, to explore the effect of N on reducing E loss with sulfur (S) as a comparison. N7IT-based OSCs achieve not only a higher PCE (13.8%), but also a much lower E loss (0.57 eV) than those of the analogue (a-IT)-based OSCs (PCE of 11.5% and E loss of 0.72 eV), which are mainly attributed to N7IT's significantly enhanced charge carrier density (promoting J SC) and largely suppressed nonradiative E loss by over 0.1 eV (enhancing V OC). In comparison, N8IT, with an extended π-conjugated length, shows relatively lower photovoltaic performance than N7IT (but higher than a-IT) due to the less favorable morphology caused by the excessively large dipole moment of the asymmetrical molecule. Finally, this work sheds light on the structure-property relationship of the N-functionalization, particularly on its effects on reducing the E loss, which could inspire the community to design and synthesize more N-functionalized SMAs.

中文翻译：

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Dithieno [3,2-b：2'，3'-d]吡咯型不对称电子受体：氮官能化对减少非辐射复合损失和偶极矩对形态的影响研究。

由辐射复合损耗（ΔE1和ΔE2）和非辐射复合损耗（ΔE3）组成的能量损耗（E loss）被认为是有机太阳能电池（OSC）的重要因素。在此，设计并合成了两个N-官能化的不对称小分子受体（SMAs），即N7IT和N8IT，以探讨N对减少硫（S）引起的E损失的影响。与基于模拟（a-IT）的OSC相比，基于N7IT的OSC不仅实现了更高的PCE（13.8％），而且还大大降低了E损失（0.57 eV）（PCE为11.5％，E损失为0.72 eV） ），这主要归因于N7IT显着提高了电荷载流子密度（促进了J SC），并大大抑制了超过0.1 eV的非辐射E损失（提高了V OC）。相比之下，N8IT具有扩展的π共轭长度，由于由不对称分子的过大偶极矩引起的形态较差，因此显示出比N7IT相对较低的光伏性能（但高于α-IT）。最后，这项工作揭示了N-官能化的结构-性质关系，特别是它对降低E损失的影响，这可以激发社区设计和合成更多N-官能化的SMA。