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PDの張さんの論文
「Photoexcited carrier dynamics in colloidal quantum dot solar cells:
insights into individual quantum dots, quantum dot solid films and devices」
がChemical Society Reviewsの表紙に抜擢されました。
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Fig. Photoexcited carrier dynamics in colloidal quantum dot solar cells
Photoexcited carrier dynamics in colloidal quantum dot solar cells: insights into individual quantum dots, quantum dot solid films and devices

The certified power conversion efficiency (PCE) record of colloidal quantum dot solar cells (QDSCs) has considerably improved from below 4% to 16.6% in the last few years. However, the record PCE value of QDSCs is still substantially lower than the theoretical efficiency. So far, there have been several reviews on recent and significant achievements in QDSCs, but reviews on photoexcited carrier dynamics in QDSCs are scarce. The photovoltaic performances of QDSCs are still limited by the photovoltage, photocurrent and fill factor that are mainly determined by the photoexcited carrier dynamics, including carrier (or exciton) generation, carrier extraction or transfer, and the carrier recombination process, in the devices. In this review, the photoexcited carrier dynamics in the whole QDSCs, originating from individual quantum dots (QDs) to the entire device as well as the characterization methods used for analyzing the photoexcited carrier dynamics are summarized and discussed. The recent research including photoexcited multiple exciton generation (MEG), hot electron extraction, and carrier transfer between adjacent QDs, as well as carrier injection and recombination at each interface of QDSCs are discussed in detail herein. The influence of photoexcited carrier dynamics on the physiochemical properties of QDs and photovoltaic performances of QDSC devices is also discussed.
  

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Yaohong Zhang, Guohua Wu, Feng Liu, Chao Ding, Zhigang Zou and Qing Shen.




Fig. Schematic illustration of hot and cold electron and hole relaxation and transfer at the FAPbI3 QDs/TiO2 and FAPbI3 QDs/NiOx heterojunctions.
Photoexcited hot and cold electron and hole dynamics at FAPbI3 perovskite quantum dots/metal oxide heterojunctions used for stable perovskite quantum dot solar cells

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 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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Naoki Nakazawa, Yaohong Zhang, Feng Liu, Chao Ding, Kanae Hori, Taro Toyoda, Yingfang Yao, Yong Zhou, Shuzi Hayase, Ruixiang Wang, Zhigang Zoub and Qing Shen




Fig. a)The device structure adopted in this study.
PEAI was used as the passivation layer on the perovskite surface.
b)Cross-sectional SEM images of PEAI-treated perovskite devices.
Growth of Amorphous Passivation Layer Using Phenethylammonium Iodide for High‐Performance Inverted Perovskite Solar Cells

Organic–inorganic lead halide perovskite solar cells have realized a rapid increase of power conversion efficiency (PCE) in the past few years. However, their performance still suffers trap‐assisted decline due to defects at the surface and grain boundaries of the perovskite film. Herein, a phenethylammonium iodide‐lead iodide (PEAI‐PbI2) passivation layer is formed on the CH3NH3PbI3 perovskite film. The characterization results indicate that the PEAI covering layer leads to the reduction of surface defects and suppression of nonradiative recombination. By manipulating this surface passivation method, a remarkably improved VOC of 1.16 V and an enhanced PCE of 20.8% are achieved.
  

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Fan Zhang, Qinxun Huang, Jun Song, Yaohong Zhang, Chao Ding, Feng Liu, Dong Liu, Xiaobin Li, Hironobu Yasuda, Koji Yoshida, Junle Qu, Shuzi Hayase, Taro Toyoda, Takashi Minemoto, and Qing Shen.




Fig. (A)Schematic diagram of the architecture of ZnO@SnO2NW-based CQDSCs. (B)The J-V curves of ZnO NW CQDSCs with or without SnO2 passivation.
Improving Photovoltaic Performance of ZnO Nanowires Based Colloidal Quantum Dot Solar Cells via SnO2 Passivation Strategy

Colloidal quantum dot solar cells (CQDSCs) based on one-dimensional metal oxide nanowires (NWs) as the electron transport layer (ETL) have attracted much attention due to their larger ETL/colloidal quantum dots (CQDs) contact area and longer electron transport length than other structure CQDSCs, such as planar CQDSCs. However, it is known that defect states in NWs would increase the recombination rate because of the high surface area of NWs. Here, the defect species on the ZnO NWs' surface which resulted in the surface recombination and SnO2 passivation effects were investigated. Comparing with the solar cells using pristine ZnO NWs, the CQDSCs based on SnO2 passivated ZnO NW electrodes exhibited a beneficial band alignment to charge separation, and the interfacial recombination at the ZnO/CQD interface was reduced, eventually resulting in a 40% improvement of power conversion efficiency (PCE). Overall, these findings indicate that surface passivation and the reduction of deep level defects in ETLs could contribute to improving the PCE of CQDSCs.

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Shuhei Ozu, Yaohong Zhang, Hironobu Yasuda, Yukiko Kitabatake, Taro Toyoda, Masayuki Hirata, Kenji Yoshino, Kenji Katayama, Shuzi Hayase, Ruixiang Wang and Qing Shen.




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