All inorganic perovskite CsPbX3 (X = Cl, Br, I) nanocrystals (NCs) have been endowed great promise for optoelectronic device applications. However, further practical applications of these NCs are blocked because of their poor stability. In the present work, we propose a novel strategy to synthesize highly luminescent and stable red-emitting CsPbBrI2/PbSe heterojunction nanocrystals (h-NCs) via an epitaxial solution growth method, in which lattice-matching condition between CsPbBrI2 and PbSe was satisfied, and each CsPbBrI2 NC was partially covered by PbSe in the CsPbBrI2/PbSe heterodimers. The ultrafast transient absorption (TA) and time-resolved photoluminescence (TRPL) spectroscopy revealed that incorporation of PbSe can modify surface and hence passivate the surface trap states of the CsPbBrI2 NCs, helping to enhance the photoluminescence quantum yields (PLQY) (up to 83.4%) of these CsPbBrI2/PbSe h-NCs. First-principle calculations based on DFT confirmed that the significantly improved stability of these CsPbBrI2/PbSe h-NCs was attributed to the strong chemical bonding of selenium atoms of PbSe and lead atoms of PbX2-terminated surface from CsPbBrI2. Thin films of these CsPbBrI2/PbSe h-NCs can maintain bright red PL brightness and cubic phase even after 15-day storage under a high humidity condition. Benefiting from the performances of high stability and luminescent efficiency, these red-emitting CsPbBrI2/PbSe h-NCs have a positive implication for bright light-emitting diodes (LEDs).
Graphical abstract
CsPbBrI2/PbSe heterojunction nanocrystals (h-NCs) show higher stability and photoluminescence quantum yield (PLQY) than those of pristine CsPbBrI2 NCs. Thin films of these CsPbBrI2/PbSe h-NCs can maintain bright red PL brightness and cubic phase even after 15-day storage under a high humidity condition, while pristine CsPbBrI2 NCs will decompose and show green PL brightness within exposure to 15 days under the same conditions.
Author(s): Jigeon Kim, Bonkee Koo, Wook Hyun Kim, Jongmin Choi, Changsoon Choi, Sung Jun Lim, Jong-Soo Lee, Dae-Hwan Kim, Min Jae Ko, Younghoon Kim
Abstract
Fully inorganic CsPbI3 perovskite quantum dots (CsPbI3-PQDs) are known as the best-performing photovoltaic absorber in colloidal quantum dot solar cells. This is achieved by improving the cubic-phase-stabilization and electronic-coupling in CsPbI3-PQD solids. In conventional approaches, the hydrolysis of methyl acetate (MeOAc) resulting in acetic acid and methanol as intermediate substances plays a key role in replacing long-chain hydrocarbons with short-chain ligands, which improves charge transport in the CsPbI3-PQD solids. However, CsPbI3-PQDs suffer from lattice distortion and instability under acidic conditions including protons and polar media, leading to CsPbI3-PQD fusion and poor photovoltaic performance. Herein, we report that electronic coupling and photovoltaic performance of CsPbI3-PQD solids are improved by efficient removal of long-chain oleate ligands using a solution of sodium acetate (NaOAc) in MeOAc, which results in the direct generation of OAc ions without forming protons and methanol. NaOAc-based ligand exchange of CsPbI3-PQDs enables preservation of their nanocrystal size without fusion and minimization of surface trap states originating from metal hydroxide formation on their surfaces. Consequently, the best solar cell comprising NaOAc-treated CsPbI3-PQDs shows an improved device performance with a power conversion efficiency (PCE) of 13.3%, as compared with a lead nitrate-treated control device (12.4% PCE).
Graphical abstract
We demonstrate that sodium acetate (NaOAc) directly generates short-chain OAc ions to exchange the long-chain oleate ligands of CsPbI3 perovskite quantum dots (CsPbI3-PQDs). NaOAc-based ligand exchange enables preservation of CsPbI3-PQD size, minimization of surface trap states, and enhancement of electronic coupling in the resultant CsPbI3-PQD solids. Consequently, NaOAc-treated CsPbI3-PQD solar cells show improved device performance with 12.4% power conversion efficiency.
by Tongming Su, Zuzeng Qin, Hongbing Ji and Zili Wu
Two-dimensional (2D) photocatalysts have attracted considerable research interest in the past
decades due to their unique optical, physical and chemical properties. Constructing 2D/2D
heterojunctions with large interface area has been considered as an effective approach to enhance
the transfer rate and the separation efficiency of the charge carriers, leading to dramatic increase
in the photocatalytic performance of the photocatalysts. Here, the state-of-the-art progress on
heterojunctions based on 2D materials is reviewed, including the photocatalysis principles using 2D
heterojunctions, the categories of 2D heterojunctions and their application in different
photocatalytic reactions, and the theoretical studies of the 2D heterojunctions. Moreover, the
advantages and disadvantages of the 2D heterojunctions are also discussed. Finally, the ongoing
challenges and opportunities for the future development of 2D photocatalysts with built-in
heterojunctions are proposed.
by Hainan Sun,
Xiaomin Xu,
Gao Chen,
Yupeng Zhou,
Hong-Ji Lin,
Chien-Te Chen,
Ran Ran,
Wei Zhou,
Zongping Shao
Double the doping: Oxygen evolution reaction (OER)‐active elements are simultaneously introduced into the B‐site and B′‐site of a B‐site‐ordered double perovskite (A2BB′O6), leading to an enhancement in the exposed reactive sites and an optimum surface chemical state. The A2BB′O6 perovskite displayed remarkably long durability and excellent OER activity.
Abstract
Double perovskites have emerged as efficient candidates for catalyzing the electrochemical oxygen evolution reaction (OER). Smart control of the composition of a B‐site ordered double perovskite can lead to improved catalytic performance. By adopting a facile co‐doping strategy, the OER‐active elements are simultaneously introduced into the B‐site and B′‐site of a B‐site‐ordered double perovskite (A2BB′O6), leading to an enhancement of the exposed reactive sites and an optimum surface chemical state. As a result, a model system built from the substitution of Co for Mo and Fe in the Sr2FeMoO6−δ double perovskite (with a composition of Sr2Fe0.8Co0.2Mo0.6Co0.4O6−δ) shows significantly enhanced OER activity in alkaline media compared with the host material, requiring an overpotential of 345 mV to reach a 10 mA cm−2 current density (catalyst loading≈0.232 mgcat cm−2GEO) and a cell voltage of 1.57 V to afford the same current density for the overall water splitting when coupled with a Pt/C cathode (catalyst loading≈2 mg cm−2). It also demonstrates excellent electrochemical stability. The generalizability of the compositional control methodology has also been demonstrated in double perovskites incorporating transition metals other than Co (e.g., Ni).
by Aniruddha Ray†‡, Daniela Maggioni?, Dmitry Baranov†, Zhiya Dang†, Mirko Prato?, Quinten A. Akkerman†, Luca Goldoni?, Enrico Caneva§, Liberato Manna*†, and Ahmed L. Abdelhady*†
by Michal Baranowski†‡, Krzysztof Galkowski†§, Alessandro Surrente†, Joanna Urban†, Lukasz Klopotowski?, Sebastian Mac´kowski§, Duncan Kennedy Maude†, Rim Ben Aich?, Kais Boujdaria?, Maria Chamarro#, Christophe Testelin#, Pabitra K. Nayak?, Markus Dollmann?, Henry James Snaith?, Robin John Nicholas*?, and Paulina Plochocka*†‡
The under-coordinated ionic defects at the surface and grain boundaries of organic-inorganic halide perovskite always attract and trap the free carriers via the electrostatic force and accelerate the ions migration by defect vacancies channels, significantly limiting the charge extraction efficiency and intrinsic stability of perovskite solar cells (PSCs). Here, a novel strategy of ionic layer induced homo-junction perovskite reinforced the build in field (Ebi) is proposed to further decrease trap recombination and suppress the ions migration, thereby enhancing the power conversion efficiencies (PCEs) and intrinsic stability of PSCs. Experiments and theories certify that the adsorbed cations and anions will not only give rise to interface charge accumulation/depletion of perovskite, resulting in boarder distributed and reinforced Ebi, but also increased the interface ions vacancy migration barriers via the extra ionic interaction. As a result, the resultant n-i-p PSCs showed a record PCE of 20.88% among the organic electron transfer layer (ETL) and deliver a high stability of 88% after aged 60 days in atmosphere without encapsulation. Our findings provide a new insight to further eliminate the side effect of ionic defects and guide to design newly contact interface to minimize the trap recombination and ions motion induced intrinsic stability of PSCs.
Traditional trial-and-error methods seriously restrict and hinder the searching of high-performance functional materials, especially when the search space is large. Rapid searching for advanced functional materials has always been a hot research topic, and attracted a lot of experimental and theoretical research attention. Here, by combining machine learning method with density functional theory (DFT) calculations, a target-driven method is proposed here to speed up the discovery of hidden hybrid organic-inorganic perovskites (HOIPs) for photovoltaic applications from 230808 HOIPs candidates which is almost two orders larger than previous studied. After imposing two criterions, i.e., charge neutrality condition and stability condition, on potential HOIPs candidates, followed by a machine learning (ML) screening, 686 orthorhombic-like HOIPs with proper bandgap are selected. In machine learning screening, ensemble learning using three ML models, including gradient boosting regression (GBR), supporting vector regression (SVR) and kernel ridge regression (KRR), are applied to predict the bandgap of 38086 HOIPs candidates. 132 stable and non-toxic (Cd-, Pb- and Hg-free) orthorhombic-like HOIPs are finally verified by DFT calculations with appropriate band gap for solar cells. In the present study, not only a series of unexplored stable and non-toxic HOIPs are discovered for further experimental synthesis, a new HOIPs database is constructed as well, thus beneficial to future functional material design.
by Bo Yin, Yongfeng Zhang, Kanzhe Li, Jingran Zhou, Caixia Liu, Min Zhang and Shengping Ruan
An FTO/TiO 2 /MoO 3 based UV detector has been fabricated through the synthesis of TiO 2 nanowires
(NWs) on FTO using the hydrothermal method, the preparation of MoO 3 on TiO 2 NWs by the
spin-coating method, after the hydrothermal synthesis, and the preparation of Ag electrodes on the
FTO and MoO 3 . The detector exhibits an excellent performance of photo-to-dark current ratio of
more than two orders of magnitude. This performance is produced because the dark current under 2.2 V
bias has been significantly inhibited due to the electronic potential well formed by the energy band
distribution while the photocurrent has increased in comparison with FTO/TiO 2 based detectors under
the same conditions which also have a higher photo-to-dark current ratio without the MoO 3 content.
Not only does this study take advantage of 1D NWs and 2D nanostructures, but it also provides a new
way to inhibit the dark curr...
by Haiying Zheng,
Huifen Xu,
Fangcai Zheng,
Guozhen Liu,
Xiaoxiao Xu,
Shendong Xu,
Liying Zhang,
Xu Pan
Call of 2 D: The influence of constituent ratios (n) and varisized ammonium salts on the performance of 2 D perovskite solar cells is investigated. The 2 D perovskite devices based on larger values of n and smaller ammonium salt sizes exhibit better photovoltaic performances. However, the moisture resistance of 2 D perovskite devices is higher when n is smaller and ammonium salts are larger in size.
Abstract
Two‐dimensional perovskite solar cells (PSCs) with high moisture resistance are a key topic in the photovoltaic field. However, their lower power conversion efficiencies (PCEs) in comparison to 3 D PSCs is still an urgent problem to be solved. It is vital to understand the impact of constituent ratios and ammonium salt sizes on the photovoltaic performance and humidity stability. Based on the formula of (RNH3)2(MA)n−1PbnI3n+1 (n=1, 3, 5, 7, 9, and 11), a series of 2 D perovskites is prepared by introducing varisized ammonium salts of ethylammonium iodide (EAI), propylammonium iodide (PAI), and butylammonium iodide (BAI). The effects of the constituent ratios and varisized ammonium salts on the properties of the 2 D perovskites were studied. 2 D perovskite devices based on larger n and smaller ammonium salt size are found to exhibit better performances. However, the moisture resistance of the 2 D perovskite devices is higher when n is smaller and the ammonium salt size is larger. Therefore, the EA2MA10Pb11I34 (n=11) 2 D perovskite device displays the best photovoltaic performance, with the highest PCE of 16.93 %, whereas BA2MA2Pb3I10 (n=3) 2 D perovskite, with the largest contact angle of 79.8°, can retain over 85 % of the initial PCE after 1440 h aging at 50 % relative humidity. This work indicates the PCE and stability of 2 D perovskites can be conveniently and effectively adjusted by controlling the 2 D constituent ratios and ammonium salt sizes, so as to obtain efficient 2 D PSCs with high stability.
by Min Zhang,
Yan-Fei Mu,
Wen Zhang,
Xiao-Xuan Guo,
Guang-Xing Dong,
Tong-Bu Lu
No sacrifices made: Low‐cost and water‐soluble lead halide perovskite nanocrystals with metal cation doping are fabricated with the assistance of a fluorocarbon agent. They exhibit not only high dispersity and stability in aqueous solution, but also efficient photocatalytic activity for visible‐light‐driven CO2 reduction in pure water without additional sacrificial reductant.
Abstract
Lead halide perovskite (LHP) nanocrystals have recently been actively investigated for photocatalysis, owing to their inexpensive fabrication and excellent optoelectronic properties. However, LHP nanocrystals have not been used for artificial photosynthesis in aqueous solution, owing to their high sensitivity to water. In this study, water‐tolerant cobalt‐doped CsPbBr3/Cs4PbBr6 nanocrystals have been prepared with the protection of hexafluorobutyl methacrylate. The resultant materials are employed as efficient photocatalysts for visible‐light‐driven CO2 reduction in pure water. The perovskite nanocrystals with 2 % cobalt doping afford an impressive overall yield of 247 μmol g−1 for photocatalytic CO2 conversion into CO and CH4, using water as an electron source. This study represents a significant step for practical artificial photosynthesis by using LHP nanocrystals as photocatalysts in aqueous solution.
by Geon Yeong Kim†?, Shinho Kim‡?, Jinyoung Choi†?, Moohyun Kim†, Hunhee Lim†, Tae Won Nam†, Wonseok Choi†, Eugene N. Cho†, Hyeuk Jin Han†, ChulHee Lee†, Jong Chan Kim§, Hu Young Jeong§, Sung-Yool Choi‡, Min Seok Jang*‡, Duk Young Jeon*†, and Yeon Sik Jung*†
by Congcong Wang, Dingke Xue, Xinyu Shen, Hua Wu, Yu Zhang, Haining Cui and William W Yu
Perovskite white light-emitting devices (WLEDs) without intercalation layers have not been achieved
due to the ion exchange. Although the intercalation layers prevent ion exchange between perovskite
nanocrystals (NCs), it also creates a new problem of charge imbalance and the structure becomes more
complex. In this study, blue emitting ZnCdS/ZnS NCs with high quantum yield and stability are
introduced to work with the yellow emission from CsPb(Br/I) 3 perovskite NCs for WLEDs. The WLEDs
are constituted of ITO/ZnO/PEI/ZnCdS/ZnS NCs/CsPb(Br/I) 3 NCs/TCTA/MoO 3 /Au. This design avoids ion
exchange between different perovskites NCs, and realizes white light emission by simple fabrication.
As a result, we achieved the white light coordinates of (0.34, 0.34) and a correlated color
temperature of 5153 K.
by Min Liao,
Bin-Bin Yu,
Zhixin Jin,
Wei Chen,
Yudong Zhu,
Xusheng Zhang,
Weitang Yao,
Tao Duan,
Igor Djerdj,
Zhubing HE
Treat yo self: Phenylethylammonium bromide (PEABr) is employed to treat pristine FASnI3 (FA=formamidinium) films, leading to formation of an ultrathin low‐dimensional perovskite layer on the surface of the pristine film and Br incorporation into the bulk of the FASnI3 film. The treatment enhances stability and conversion efficiency from 4.77 to 7.86 %.
Abstract
The promising tin perovskite solar cells (PSCs) suffer from the oxidation of Sn2+ to Sn4+, leading to a disappointing conversion efficiency along with poor stability. In this work, phenylethylammonium bromide (PEABr) was employed to form an ultrathin, low‐dimensional perovskite layer on the surface of the FASnI3 (FA=formamidinium) absorber film to improve the interface of perovskite/PCBM ([6,6]‐phenyl‐C61‐butyricacid methyl) in the inverted planar device structure of the ITO (indium‐doped tin oxide)/PEDOT:PSS [poly(3,4‐ethylenedioxythiophene)/polystyrene sulfonate]/perovskite/[6,6]‐phenyl‐C61‐butyricacid methyl (PCBM)/BCP (2,9‐dimethyl‐4,7‐diphenyl‐1,10‐phenanthroline) electrode. The device efficiency was enhanced from 4.77 to 7.86 % by this PEABr treatment. A series of characterizations proved that this modification could improve the crystallinity of the FASnI3 perovskite by incorporating Br and forming an ultrathin, low‐dimensional perovskite layer at the interface, which led to the effective suppression of Sn2+ oxidation, improved band level alignment, and decreased defect density. These effects contributed to the clear enhancement of conversion efficiency. Moreover, this treatment also led to remarkably enhanced device stability, with approximately 80 % of the initial efficiency retained after 350 h light soaking, whereas the control device failed within 140 h. This work deepens our understanding of the suppression effect of PEABr on the oxidation of Sn2+ and paves a new way to fabricate promising tin halide PSCs by facile interface engineering.
