Leng Jing, Liu Junxue, Zhang Jun, Jin Shengye
State Key Laboratory of Molecular Reaction Dynamics and Collaborative Innovation Center of Chemistry for Energy Materials (iChEM), Dalian Institute of Chemical Physics, Chinese Academy of Sciences , Dalian 116023, China.
State Key Laboratory of Heavy Oil Processing, College of Chemical Engineering, China University of Petroleum , 66 Changjiang West Road, Huangdao District, Qingdao 266580, China.
J Phys Chem Lett. 2016 Dec 15;7(24):5056-5061. doi: 10.1021/acs.jpclett.6b02309. Epub 2016 Nov 29.
In a perovskite solar cell, the overall photoinduced charge-transfer (CT) process comprises both charge diffusion through the bulk to perovskite/electrode interfaces and interfacial electron and hole transfer to electrodes. In this study, we decoupled these two entangled processes by investigating the film thickness-dependent CT dynamics from CHNHPbI perovskites to [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) (electron acceptor) and spiro-OMeTAD (hole acceptor). By fitting ultrafast transient absorption kinetics to an explicit "diffusion-coupled charge-transfer" model, we found that the charge diffusion from the film interior to perovskite/electrode interfaces took ∼200 ps to a few nanoseconds, depending on the thickness of perovskite film; the subsequent interfacial charge transfer was ultrafast, ∼6 ps for electron transfer to PCBM and ∼8 ps for hole transfer to spiro-OMeTAD, and led to efficient charge extraction (>90%) to electrodes in a 400 nm thick film. Our results indicate that the picosecond interfacial charge transfer is a key to high-performance perovskite solar cells.
在钙钛矿太阳能电池中，整体光致电荷转移（CT）过程包括电荷通过本体扩散到钙钛矿/电极界面以及界面电子和空穴转移到电极。在本研究中，我们通过研究从CHNHPbI钙钛矿到[6,6]-苯基-C61-丁酸甲酯（PCBM，电子受体）和螺环-OMeTAD（空穴受体）的薄膜厚度依赖性CT动力学，将这两个相互纠缠的过程解耦。通过将超快瞬态吸收动力学拟合到一个明确的“扩散耦合电荷转移”模型，我们发现从薄膜内部到钙钛矿/电极界面的电荷扩散需要约200皮秒到几纳秒，这取决于钙钛矿薄膜的厚度；随后的界面电荷转移非常快，电子转移到PCBM约为6皮秒，空穴转移到螺环-OMeTAD约为8皮秒，并导致在400纳米厚的薄膜中高效地将电荷提取（>90%）到电极。我们的结果表明，皮秒级的界面电荷转移是高性能钙钛矿太阳能电池的关键。
