Photoexcited Hot and Cold Electron and Hole behavior at FAPbI3 Perovskite Quantum Dots/Metal Oxide Heterojunctions: Hot versus Cold Charge‐relaxation and transfer
Chao Ding a, Xing Lin a, Feng Liu a, Yaohong Zhang a, Daisuke Hirotani b, Taro Toyoda a, Shuzi Hayase a, Takashi Minemoto c, Taizo Masuda d, Kenji Katayama e, Qing Shen a
a The University of Electro-Communications, Japan, Japan
b Kyushu Institute of Technology, Japan, 204 Hibikino Wakamatsu-ku, Kitakyushu - Fukuoka, 808, Japan
c Department of Photonics, Ritsumeikan University, Kyoto
d X-Frontier Division, Toyota Motor Corporation, Shizuoka
e Department of Applied Chemistry, Chuo University
Asia-Pacific International Conference on Perovskite, Organic Photovoltaics and Optoelectronics
Proceedings of Asia-Pacific International Conference on Perovskite, Organic Photovoltaics and Optoelectronics (IPEROP20)
Tsukuba-shi, Japan, 2020 January 20th - 22nd
Organizers: Michio Kondo and Takurou Murakami
Poster, Xing Lin, 080
Publication date: 14th October 2019

 

Highly luminescent formamidinium lead iodide (FAPbI3) quantum dots (QDs) exhibit optimum stability and narrowest bandgap energy among lead halide perovskites, thus they have become one of the most promising materials for the development of light-harvesting and near infrared-emitting devices.1, 2 Several studies exploring the photoelectronic characteristics of FAPbI3 QDs, e.g., multiple exciton generation (MEG)3, hot carrier relaxation4 and exciton–phonon coupling5 have been performed. However, given the importance of the heterojunction where the main charge separation within FAPbI3 QDs based solar cell devices, little is known about the photoexcited carriers transfer dynamics at the interface.

 

By using transient absorption (TA) spectroscopy, we systematically investigate both hot and cold photoexcited carrier (electron and hole) dynamics including relaxation and transfer at the heterojunction interfaces between FAPbI3 QDs and two kinds of well used charge acceptors, i.e., TiO2 and NiOx. We find that (i) the hot carriers in the FAPbI3 QDs are cooled to cold carriers with a cooling rate in the order of 1011 s−1, and (ii) the cold-electron and -hole injection rates are size dependent and are 2.01~2.29 × 109 s−1 and 1.55~1.96 × 109 s−1 at the two types of FAPbI3 QD/MO (metal oxide) heterojunctions, respectively, which are in good agreements with Marcus theory of charge transfer. In addition, the photoexcited carrier injection efficiency at the two heterojunctions is found to be as high as over 99%, which is the most important key for achieving high photovoltaic performance of the FAPbI3 QD solar cells (QDSCs). Prototypes of the two types of heterojunction-based QDSCs, i.e., normal-structure solar cells based on FAPbI3 QD/TiO2 and inverted-structure solar cells based on FAPbI3 QD/NiOx, were developed and the power conversion efficiencies of more than 9% and 5% were obtained, respectively. Moreover, the photovoltaic performance showed a higher storage stability over 100 days. The photovoltaic performance would be improved largely by optimization of each parts in the QDSCs. Our results shed light on perovskite QD-based optoelectronic devices.

 

 

  

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