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