Interface Architecture between TiO2/Perovskite,Perovskite/Hole Transport Layer, and Perovskite Grain Boundary for MAPbI3, MASnPbI3 and CsPbI3 Solar Cells

Daisuke Hirotani^b, Masahiro Moriya^b, Yuhei Ogomi^b, Teresa Ripolles^b, Shuzi Hayase^c, Taro Toyoda^c, Qing Shen^c, Kenji Yoshino^d, Takashi Minemoto

^aRitumeikan Univeristy, 1-1-1 Noji-higashi, Kusatsu Shiga 525-8577

^bKyushu Institute of Technology, Japan, 204 Hibikino Wakamatsu-ku, Kitakyushu - Fukuoka, 808, Japan

^cUniversity of Electro-communication, 1-5 Chofugaoka, Chofu, Yokyo

^dUniversity of Miyazaki, 1-1 Gakuen Kibanadai, Miyazaki, 889, Japan

International Conference on Hybrid and Organic Photovoltaics
Proceedings of International Conference on Hybrid and Organic Photovoltaics (HOPV16)

Swansea, United Kingdom, 2016 June 29th - July 1st

Organizers: James Durrant, Henry Snaith and David Worsley

Oral, Shuzi Hayase, presentation 013
Publication date: 28th March 2016

The relationship between photovoltaic performances and interface structures on MAPbI₃, CsPbI₃, and MAPbSnI₃ are reported. In addition, role of Cl anions are at the interfaces are discussed. In order to examine the interface structure, quartz crystal microbalance sensor (QCM) was used. The amount of PbI₂ adsorption on TiO₂ surface increased as the adsorption time and leveled off at a certain time. PbI₂ still remained even after the solvent only (DMF) was passed on the TiO₂ layer on QCM (namely rinsing with DMF), suggesting that the PbI₂ was tightly bonded on the TiO₂ surface. The structure was found to be Ti-O-Pb linkage by XPS analysis. We concluded that the Ti-OH on the surface of TiO₂ reacts with I-Pb-I to form Ti-O-Pb-I. The surface trap density was measured by thermally stimulated current (TSC) method. Before the PbI2 passivation, the trap density of TiO₂ was 10¹⁹ cm³. The trap density decreased to 10¹⁶/cm³ after the PbI₂ passivation, suggesting that the TiO₂ surface trap was passivated with I-Pb-I. It was found that Jsc increased with an increase in the Ti-O-Pb density. We concluded that the interface between TiO₂ and perovskite layer has passivation structure consisting of Ti-O-Pb-I which decreases the trap density of the interfaces and suppresses charge recombination. The effect of Cl anion on high efficiency is still controversial when perovskite layer is prepared by one step method from the mixture of MAI and PbCl₂. It was found that adsorption density of PbCl₂ on TiO₂ surface was much higher than that of PbI₂ from the experiment using QCM sensor. After the surface was washed with DMF, Cl and Pb were detected. These results suggest that the TiO₂ surface was much more passivated by PbCl₂ than by PbI₂. This may explain partially the high efficiency when the perovskite layer was fabricated by one step process consisting of MAI and PbCl₂ solution. We also observed that the crystal size increased with an increase in the amount of Cl anion which of course one of the explanation of the high efficiency. The interface of hole transport layer/perovskite layer, and between perovskite layer /perovskite layer (grain boundary) was passivated with organic amines in the same way. The passivation was also effective for increasing Voc and Jsc (Efficiency: 17.5%). This was explained by the results of transient absorption spectroscopy that the charge recombination time between hole transport payer/perovskite layer increased from 0.3 to 60 μsec.

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