Decomposition of Organometal Halide Perovskite Films on Zinc Oxide Nanoparticles.
Solution processed zinc oxide (ZnO) nanoparticles (NPs) with excellent electron transport properties and a low-temperature process is a viable candidate to replace titanium dioxide (TiO2) as electron transport layer to develop high-efficiency perovskite solar cells on flexible substrates. However, the number of reported high-performance perovskite solar cells using ZnO-NPs is still limited. Here we report a detailed investigation on the chemistry and crystal growth of CH3NH3PbI3 perovskite on ZnO-NP thin films. We find that the perovskite films would severely decompose into PbI2 upon thermal annealing on the bare ZnO-NP surface. X-ray photoelectron spectroscopy (XPS) results show that the hydroxide groups on the ZnO-NP surface accelerate the decomposition of the perovskite films. To reduce the decomposition, we introduce a buffer layer in between the ZnO-NPs and perovskite layers. We find that a commonly used buffer layer with small molecule [6,6]-phenyl-C61-butyric acid methyl ester (PC61BM) can slow down but cannot completely avoid the decomposition. On the other hand, a polymeric buffer layer using poly(ethylenimine) (PEI) can effectively separate the ZnO-NPs and perovskite, which allows larger crystal formation with thermal annealing. The power conversion efficiencies of perovskite photovoltaic cells are significantly increased from 6.4% to 10.2% by replacing PC61BM with PEI as the buffer layer.
Department of Physics and Materials Science, City University of Hong Kong , Hong Kong SAR, P. R. China.
Yuanhang
Y
Cheng
Department of Physics and Materials Science, City University of Hong Kong , Hong Kong SAR, P. R. China.
Qing-Dan
QD
Yang
Institute of Polymer Optoelectronic Materials and Devices, State Key Laboratory of Luminescent Materials and Devices, South China University of Technology , Guangzhou 510640, P. R. China.
Jingyang
J
Xiao
Institute of Polymer Optoelectronic Materials and Devices, State Key Laboratory of Luminescent Materials and Devices, South China University of Technology , Guangzhou 510640, P. R. China.
Qifan
Q
Xue
Department of Physics and Materials Science, City University of Hong Kong , Hong Kong SAR, P. R. China.
Ho-Wa
HW
Li
Department of Physics and Materials Science, City University of Hong Kong , Hong Kong SAR, P. R. China.
Zhiqiang
Z
Guan
Institute of Polymer Optoelectronic Materials and Devices, State Key Laboratory of Luminescent Materials and Devices, South China University of Technology , Guangzhou 510640, P. R. China.
Hin-Lap
HL
Yip
Department of Physics and Materials Science, City University of Hong Kong , Hong Kong SAR, P. R. China.
Sai-Wing
SW
Tsang
buffer layer; decomposition; perovskite solar cell; poly(ethylenimine); zinc oxide nanoparticles