Surface Analytical Investigation on Organometal Triiodide Perovskite
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Surface Analytical Investigation on Organometal Triiodide Perovskite Youzhen Li,1 Xuemei Xu,1 Chenggong Wang,2 Congong Wang,2 Fangyan Xie,3 Jinsong Huang,4 Yongli Gao2,* 1 School of Physics and Electronics, Central South University, Changsha, Hunan, 410083, P.R. China 2 Department of Physics and Astronomy, University of Rochester, Rochester, NY, 14627，USA 3 Instrumental Analysis Center, Sun Yat-Sen University, Guangzhou, 510275, P.R. China 4 Department of Mechanical and Materials Engineering and Nebraska Center for Materials and Nanoscience, University of Nebraska-Lincoln, Lincoln, Nebraska 68588-0656, USA *
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ABSTRACT Lead halide perovskites have proven their great power conversion efficiency (PCE) in the last few years and attracted more and more attentions. Evaporation is an important method to get high quality perovskite films, especially for surface and interface investigation, which is important for the solar cell performance. In this paper, we present our investigations on growing PbI2 and CH3NH3I films by evaporation, and then CH3NH3PbI3 films by co-evaporation. X-ray photoemisson spectroscopy (XPS) was used to characterize the films. The results showed that CH3NH3I film was not stable in vacuum. Both N and I decreased in vacuum with time elapsing. PbI2 and CH3NH3PbI3 films are quite stable. The atomic ratio of CH3NH3PbI3 films (C: N: Pb: I =1.29:1.07:1.00:2.94) is very close to the ideal CH3NH3PbI3, which indicates that evaporation is a good method to get high quality perovskite films with accurate atomic ratio. INTRODUCTION Lead halide perovskites, (CH3NH3PbX3, X=Cl, Br, I), have attracted more and more attention as light-harvesting materials for solar cells[1-5]. The advantages of those compounds are their wide light-absorption spectra, high efficiencies and low costs[6-9]. During the last 4 years, the PCE of lead halide provskite based photovoltaic devices has increased from 3.8%[10] to 15.4%[11], and some even gets to 19.3%[12]. This is very close to the PCE of the best silicon solar cell. Perovskite solar cells have evolved from dye-sensitized solar cells. Mesoporous TiO2 and Al2O3 are usually used as scaffold to achieve high efficiency, which was termed as “mesosuperstructured solar cell” by Snaith[13]. With optimization of processing, meso-superstructured solar cells can reach more than 12% efficiency[14]. Recently, researchers found that using perovskite films as a light absorber, planar heterojunction solar cell without mesostructure can also get around 5% efficiency[14]. This means that perovskite solar cells can be fabricated in an easier way with lower cost. Many new kinds of perovskite solar cells with planar heterojunction structure have been fabricated in the last 2 years, such as lead free perovskite[15,16],holeconductor-free perovskite[17] etc.. Solution spincast is the most common method to get perovskite solar cell for its low cost and high fabrication efficiency. But usually, perovskite films with uniform surface and accurate atomic ratio can not be obtaine
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