Panhans Michel, Hutsch Sebastian, Benduhn Johannes, Schellhammer Karl Sebastian, Nikolis Vasileios C, Vangerven Tim, Vandewal Koen, Ortmann Frank
Center for Advancing Electronics Dresden, Technische Universität Dresden, 01062, Dresden, Germany.
Dresden Integrated Center for Applied Physics and Photonic Materials (IAPP) and Institute for Applied Physics, Technische Universität Dresden, Nöthnitzer Str. 61, 01187, Dresden, Germany.
Nat Commun. 2020 Mar 20;11(1):1488. doi: 10.1038/s41467-020-15215-x.
The low-energy edge of optical absorption spectra is critical for the performance of solar cells, but is not well understood in the case of organic solar cells (OSCs). We study the microscopic origin of exciton bands in molecular blends and investigate their role in OSCs. We simulate the temperature dependence of the excitonic density of states and low-energy absorption features, including low-frequency molecular vibrations and multi-exciton hybridisation. For model donor-acceptor blends featuring charge-transfer excitons, our simulations agree very well with temperature-dependent experimental absorption spectra. We unveil that the quantum effect of zero-point vibrations, mediated by electron-phonon interaction, causes a substantial exciton bandwidth and reduces the open-circuit voltage, which is predicted from electronic and vibronic molecular parameters. This effect is surprisingly strong at room temperature and can substantially limit the OSC's efficiency. Strategies to reduce these vibration-induced voltage losses are discussed for a larger set of systems and different heterojunction geometries.
光吸收光谱的低能边缘对太阳能电池的性能至关重要，但在有机太阳能电池（OSC）中尚未得到很好的理解。我们研究了分子共混物中激子带的微观起源，并研究了它们在有机太阳能电池中的作用。我们模拟了激子态密度和低能吸收特征的温度依赖性，包括低频分子振动和多激子杂化。对于具有电荷转移激子的模型供体-受体共混物，我们的模拟结果与温度相关的实验吸收光谱非常吻合。我们揭示，由电子-声子相互作用介导的零点振动的量子效应会导致可观的激子带宽，并降低开路电压，这是根据电子和振动分子参数预测的。这种效应在室温下出奇地强烈，并且会严重限制有机太阳能电池的效率。针对更多系统和不同异质结几何结构，讨论了减少这些振动引起的电压损失的策略。
