Li Yu, Yan Weibo, Li Yunlong, Wang Shufeng, Wang Wei, Bian Zuqiang, Xiao Lixin, Gong Qihuang
Institute of Modern Optics &State Key Laboratory for Artificial Microstructure and Mesoscopic Physics, School of Physics, Peking University, Beijing 100871, China.
State Key Laboratory of Rare Earth Materials Chemistry and Applications, College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, China.
Sci Rep. 2015 Sep 29;5:14485. doi: 10.1038/srep14485.
In high performance perovskite based solar cells, CH3NH3PbI3 is the key material. We carried out a study on charge diffusion in spin-coated CH3NH3PbI3 perovskite thin film by transient fluorescent spectroscopy. A thickness-dependent fluorescent lifetime was found. By coating the film with an electron or hole transfer layer, [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) or 2,2',7,7'-tetrakis(N,N-di-p-methoxyphenylamine)-9,9'-spirobifluorene (Spiro-OMeTAD) respectively, we observed the charge transfer directly through the fluorescence quenching. One-dimensional diffusion model was applied to obtain long charge diffusion distances in thick films, which is 1.7 μm for electrons and up to ~6.3 μm for holes. Short diffusion distance of few hundreds of nanometer [corrected] was also observed in thin films. This thickness dependent charge diffusion explained the formerly reported short charge diffusion distance (100 nm) in films and resolved its confliction to thick working layer (300-500 nm) in real devices. This study presents direct support to the high performance perovskite solar cells and will benefit the devices' design.
在高性能钙钛矿基太阳能电池中，CH3NH3PbI3是关键材料。我们通过瞬态荧光光谱法对旋涂CH3NH3PbI3钙钛矿薄膜中的电荷扩散进行了研究。发现了荧光寿命与厚度有关。通过分别用电子或空穴传输层[6,6]-苯基-C61-丁酸甲酯（PCBM）或2,2',7,7'-四（N,N-二对甲氧基苯胺）-9,9'-螺二芴（Spiro-OMeTAD）涂覆薄膜，我们通过荧光猝灭直接观察到了电荷转移。应用一维扩散模型来获得厚膜中的长电荷扩散距离，电子的扩散距离约为1.7μm，空穴的扩散距离高达约6.3μm。在薄膜中也观察到了几百纳米[校正后]的短扩散距离。这种与厚度有关的电荷扩散解释了先前报道的薄膜中短电荷扩散距离（约100nm），并解决了其与实际器件中厚工作层（300 - 500nm）的矛盾。本研究为高性能钙钛矿太阳能电池提供了直接支持，并将有利于器件的设计。
