Hinrichsen Ture F, Chan Christopher C S, Ma Chao, Paleček David, Gillett Alexander, Chen Shangshang, Zou Xinhui, Zhang Guichuan, Yip Hin-Lap, Wong Kam Sing, Friend Richard H, Yan He, Rao Akshay, Chow Philip C Y
Cavendish Laboratory, University of Cambridge, Cambridge, CB3 0HE, UK.
Department of Physics, The Hong Kong University of Science and Technology, Clear Water Bay,, Hong Kong, China.
Nat Commun. 2020 Nov 5;11(1):5617. doi: 10.1038/s41467-020-19332-5.
Organic solar cells based on non-fullerene acceptors can show high charge generation yields despite near-zero donor-acceptor energy offsets to drive charge separation and overcome the mutual Coulomb attraction between electron and hole. Here, we use time-resolved optical spectroscopy to show that free charges in these systems are generated by thermally activated dissociation of interfacial charge-transfer states that occurs over hundreds of picoseconds at room temperature, three orders of magnitude slower than comparable fullerene-based systems. Upon free electron-hole encounters at later times, both charge-transfer states and emissive excitons are regenerated, thus setting up an equilibrium between excitons, charge-transfer states and free charges. Our results suggest that the formation of long-lived and disorder-free charge-transfer states in these systems enables them to operate closely to quasi-thermodynamic conditions with no requirement for energy offsets to drive interfacial charge separation and achieve suppressed non-radiative recombination.
基于非富勒烯受体的有机太阳能电池，尽管供体 - 受体能量差接近零以驱动电荷分离并克服电子与空穴之间的相互库仑吸引力，但仍能显示出高电荷产生率。在此，我们使用时间分辨光谱表明，这些系统中的自由电荷是由界面电荷转移态的热激活解离产生的，该过程在室温下发生数百皮秒，比类似的基于富勒烯的系统慢三个数量级。在稍后的时间自由电子 -空穴相遇时，电荷转移态和发射激子都会再生，从而在激子、电荷转移态和自由电荷之间建立平衡。我们的结果表明，这些系统中长寿命且无无序的电荷转移态的形成，使它们能够在接近准热力学条件下运行，无需能量差来驱动界面电荷分离并实现抑制非辐射复合。
