Effects of TiO 2 Properties on Performance of CH 3 NH 3 PbI 3 Perovskite Photovoltaic Cells
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Effects of TiO2 Properties on Performance of CH3NH3PbI3 Perovskite Photovoltaic Cells Hasyiya K. Adli1, Takashi Harada1, Seigo Ito2, Shuji Nakanishi1, Shigeru Ikeda1 Research Center for Solar Energy Chemistry, Osaka University, 1-3 Machikaneyama, Toyonaka, Osaka 560-8531, Japan. 2 Department of Electric Engineering and Computer Science, Graduate School of Engineering, University of Hyogo, 2167 Shosha, Himeji, Hyogo 671-2280, Japan. 1
ABSTRACT The effects of TiCl4 post-treatment on the physicochemical properties of porous TiO2 (pTiO2) layers fabricated at 300 °C and 400 °C (denoted as pTiO2(300) and pTiO2(400), respectively) in CH3NH3PbI3 perovskite photovoltaic cells were investigated. Water contents (physisorbed water and water derived from surface hydroxyl groups) of pTiO2(300) and pTiO2(400) before and after TiCl4 post-treatment were measured by using temperature desorption spectroscopy (TDS). Moreover, structural analysis of the CH3NH3PbI3 perovskite part was performed by X-ray diffraction (XRD). In the case of pTiO2(300), the content of water was increased by the TiCl4 post-treatment due to the removal of residual organic compounds that existed before the treatment. It then caused a change in the surface activity of pTiO2(300) and enhancement of solar cell performance and photocurrent density, though suppression of CH3NH3PbI3 perovskite formation occurred. In comparison, contents of water were decreased for pTiO2(400), leading to enhancement of the conversion of PbI2 to CH3NH3PbI3 perovskite. As a result, there were significant increases in short circuit current density (Jscs) and PCEs. The results showed that TiCl4 post-treatment is an effective approach to prepare high-performance CH3NH3PbI3 perovskite solar cells without heat treatment at a very high temperature. INTRODUCTION Owing to the attractive features of cost effectiveness, ease of fabrication and superb photovoltaic performance, solar cell materials based on organic-inorganic triiodide perovskite, CH3NH3PbI3, have been dominating the solar cell field since its breakthrough [1]. The performance of these solar cells has shown a linear rate of increase with an increase in power efficiency (PCE) from 3.8% to 20.1% since the first report in 2009 [2]. Despite promising high PCEs, the issue of severe degradation of CH3NH3PbI3 perovskite solar cells has become a major drawback to their commercialization. In the presence of appreciable moisture, CH3NH3PbI3 perovskite compounds undergo rapid decomposition to yellowish PbI2, causing a significant drop of PCE [3]. There is still limited information on its degradation mechanism and the best approach to improve its stability. Recently, we found that the amount of the surface OH group (OHsurface) and porosity of the pTiO2 layer are also crucial factors for effective conversion of CH3NH3PbI3 perovskite from PbI2 and for obtaining better performance of CH3NH3PbI3 perovskite solar cells [4]. At a higher calcination temperature of pTiO2, the amount of physisorbed water (H2Ophysisorbed) and the OHsurface group graduall
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