Charge Carrier Trapping at Surface Defects of Perovskite Solar Cell Absorbers: A First-Principles Study
Hiroki Uratani a b, Koichi Yamashita a b
a CREST-JST, 7 Gobancho, Chiyoda-ku, Tokyo, 1020076, Japan
Asia-Pacific International Conference on Perovskite, Organic Photovoltaics and Optoelectronics
Proceedings of International Conference Asia-Pacific Hybrid and Organic Photovoltaics (AP-HOPV17)
Yokohama-shi, Japan, 2017 February 2nd - 4th
Organizers: Tsutomu Miyasaka and Iván Mora-Seró
Poster 052
Publication date: 7th November 2016

Charge carrier trapping at defects on surfaces or grain boundaries is detrimental for the performance of perovskite solar cells (PSCs). In practice, it is one of the main limiting factors for carrier lifetime. Also, it causes hysteresis in the current-voltage curves, which has been considered as a serious issue for operation of PSCs.

In this work, types of surface defects responsible for carrier trapping are clarified by comprehensive first-principles investigation into surface defects of tetragonal CH3NH3PbI3 (MAPbI3).

Considering defect formation energetics, it was revealed that different types of surface defects are responsible for carrier trapping, depending on the conditions: MAI-rich, intermediate, and PbI2-rich. Under MAI-rich condition, excessive I atoms on surfaces act as carrier traps. Under PbI2-rich condition, excessive Pb atoms or I atom vacancies do, however, they have somewhat higher formation energy. Under intermediate condition, any carrier-trapping surface defects have high formation energy, i.e. cannot be easily formed.

From the above, PbI2-rich condition is preferred to MAI-rich one, consistent with the superiority of the two-step device fabrication method to the one-step one in terms of the photovoltaic performance. Also, it can be proposed that intermediate condition has possibility to be the best choice.



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