Klein Johannes R, Scholz Mirko, Oum Kawon, Lenzer Thomas
Universität Siegen, Physikalische Chemie, Adolf-Reichwein-Str. 2, 57076 Siegen, Germany.
Phys Chem Chem Phys. 2017 Jul 21;19(27):17952-17959. doi: 10.1039/c7cp02459b. Epub 2017 Jun 30.
Organic-inorganic hybrid lead halide perovskites already reach very high power conversion efficiencies above 22% on architectures employing mesoporous TiO, but the carrier injection processes across the different interfaces are still not fully understood. Here we use ultrafast broadband transient absorption spectroscopy to determine time constants and yields for hole and electron injection. We show that hole transfer from the perovskite valence band (VB) to the hole-transport material (HTM) H101 at the perovskite/HTM interface occurs in less than 500 fs, but is limited by imperfections of the contact layer and poor infiltration of the HTM into the mesoporous structure. Electron injection from the perovskite conduction band (CB) into the CB of mesoporous TiO is only a small channel (25%). Electron transport inside mesoporous MAPI/TiO architectures therefore mainly occurs via the perovskite. We also show that electron injection from H101 into the perovskite is feasible for excitation at 400 nm resulting in light-harvesting of high-energy photons by the HTM. Accurate absolute NIR absorption coefficients for CB electrons in mesoporous TiO are provided.
在采用介孔TiO的结构上，有机-无机杂化铅卤化物钙钛矿已经实现了超过22%的非常高的功率转换效率，但不同界面间的载流子注入过程仍未被完全理解。在此，我们使用超快宽带瞬态吸收光谱来确定空穴和电子注入的时间常数及产率。我们表明，在钙钛矿/空穴传输材料（HTM）界面处，空穴从钙钛矿价带（VB）转移到HTM H101的过程发生在不到500飞秒的时间内，但受到接触层缺陷以及HTM向介孔结构中渗透不良的限制。从钙钛矿导带（CB）向介孔TiO的CB注入电子只是一个小通道（25%）。因此，介孔MAPI/TiO结构内部的电子传输主要通过钙钛矿进行。我们还表明，对于400nm处的激发，从H101向钙钛矿注入电子是可行的，这使得HTM能够捕获高能光子。文中还给出了介孔TiO中CB电子准确的绝对近红外吸收系数。
