Journal of Physical Chemistry C
Journal of Physical Chemistry C
5 years ago

Minute-Scale Degradation and Shift of Valence-Band Maxima of (CH3NH3)SnI3 and HC(NH2)2SnI3 Perovskites upon Air Exposure

Minute-Scale Degradation and Shift of Valence-Band Maxima of (CH3NH3)SnI3 and HC(NH2)2SnI3 Perovskites upon Air Exposure
Akinori Saeki, Yukie Katsuki, Naoki Ishida, Atsushi Wakamiya, Ryosuke Nishikubo
The development of lead-free, tin-based perovskite solar cells is becoming a pervasive topic; however, the inherent instabilities of such cells have prevented a boost of their power conversion efficiency and a deeper understanding of their fundamental properties. By using the photoelectron yield spectroscopy (PYS) and flash-photolysis time-resolved microwave conductivity (TRMC) techniques, we investigate the effects of air exposure on the valence-band maxima (VBMs) and photoconductivities of tin iodide perovskites (methylammonium cation, MASnI3; formamidinium cation, FASnI3). These perovskites exhibit a shift of the VBM (e.g., from −5.02 eV at 0 min to −5.17 eV at 18 min), deterioration of the PYS profiles, and progressive decrease of the TRMC transients on the minute scale of air exposure. The addition of SnF2 was found to suppress the initial defect-related density of the filled electronic states of MASnI3 and FASnI3, as revealed by PYS, and to partly mitigate the degradation of MASnI3, as revealed by TRMC. A low-dimensional perovskite (MA2SnI6) composed of the oxidized form of Sn(IV) was also evaluated to explain the anomalous TRMC behavior of the air-exposed MASnI3. Our results provide an important basis for correlation with the degradation and energetics of a device.

Publisher URL: http://dx.doi.org/10.1021/acs.jpcc.7b06294

DOI: 10.1021/acs.jpcc.7b06294

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