Photoexcited hot and cold electron and hole dynamics at FAPbI3 perovskite quantum dots/metal oxide heterojunctions used for stable perovskite quantum dot solar cells. (January 2020)

• Record Type: Journal Article
• Authors: Ding, Chao; Liu, Feng; Zhang, Yaohong; Hirotani, Daisuke; Rin, Xing; Hayase, Shuzi; Minemoto, Takashi; Masuda, Taizo; Wang, Ruixiang; Shen, Qing
• Is Part Of: Nano energy. Volume 67(2020)
• Publication Date: 2020-01
• Subjects: Charge transfer -- Hot carriers -- Heterojunction -- Quantum dots -- Perovskite solar cells; Nanoscience -- Periodicals; Nanotechnology -- Periodicals; Nanostructured materials -- Periodicals; Power resources -- Technological innovations -- Periodicals; Nanoscience; Nanostructured materials; Nanotechnology; Power resources -- Technological innovations; Periodicals; 621.042
• DOI: 10.1016/j.nanoen.2019.104267
• Languages: English
• ISSNs: 2211-2855

Abstract

Abstract: Highly luminescent formamidinium lead iodide (FAPbI3 ) quantum dots (QDs) exhibit high stability and narrowest bandgap energy among lead halide perovskites, thus they have become one of the most promising materials for the development of perovskite QD-based light-harvesting and near infrared-emitting devices. However, little is known thus far about photoexcited carrier dynamics at the interface between FAPbI3 QDs and charge transport layers, which is very important for both fundamental studies and applications of the QD/charge transport layer heterojunctions. Here, 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 10 11 s −1, and (ii) the cold-electron and -hole injection rates are size dependent and are 2.01–2.29 × 10 9 s −1 and 1.55–1.96 × 10 9 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. Graphical abstract: 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 are investigated systematically. The hot carriers in the FAPbI3 QDs are cooled to cold carriers with a cooling time of more than 60 ps. The cold-electron and -hole injection rates are size dependent and are 2.01–2.29 × 10 9 s −1 and 1.55–1.96 × 10 9 s −1 at the two types of FAPbI3 QD/MO (metal oxide) heterojunctions, respectively. 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. Image 1 Highlights: The photoexcited carrier dynamics of FAPbI3 QDs at two kinds of QDs/metal oxide heterojunctions have been investigated. The photoexcited electron and hole injection efficiencies from the FAPbI3 QDs to TiO2 and NiOx are as high as 99%. Prototypes of the two heterojunction-based QD solar cells were developed and the efficiencies were 9% and 5%, respectively. The photovoltaic performance of the FAPbI3 QD-based solar cells showed a higher storage stability over 100 days.