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Stable Inorganic Colloidal Tin and Tin–Lead Perovskite Nanocrystals with Ultralong Carrier Lifetime via Sn(IV) Control

Yusheng Li, Dandan Wang, Yongge Yang, Chao Ding, Yuyu Hu, Feng Liu, Yuyao Wei, Dong Liu, Hua Li, Guozheng Shi, Shikai Chen, Hongshi Li, Akihito Fuchimoto, Keita Tosa, Unno Hiroki, Shuzi Hayase, Huiyun Wei, and Qing Shen


Fig. Stable CsSnI3 nanocrystals exhibit ultralong carrier lifetimes due to Sn(IV) control.



Inorganic tin (Sn) perovskite nanocrystals offer a promising solution to the potential toxicity concerns associated with their established lead (Pb)-based counterparts. Yet, achieving their superior stability and optoelectronic properties remains an ongoing challenge. Here, we report a synthesis of high-symmetry α-phase CsSnI3 nanocrystals with an ultralong 278 ns carrier lifetime, exceeding previous benchmarks by 2 orders of magnitude through meticulous Sn(IV) control. The nanocrystals demonstrate excellent colloidal stability, uniform monodispersity, and a distinct exciton peak. Central to these outcomes is our designed solid–liquid antioxidation suspension of tri-n-octylphosphine (TOP) and zerovalent tin (Sn(0)) that fully addresses the unique coexisting oxygen-driven and solvent-driven Sn oxidation mechanisms in Sn perovskite nanocrystal synthesis. We uncover the largely undervalued function of TOP in mitigating oxygen-driven Sn oxidation and introduce Sn(0) powder to generate a synergistic antioxidation function with TOP, significantly reducing Sn(IV)-induced defects and distortions and contributing to enhanced optoelectronic properties. Strikingly, this approach also profoundly impacts inorganic Sn–Pb perovskite nanocrystals, boosting lifetimes by 2 orders of magnitude and increasing photoluminescence quantum yield over 100-fold to 35%. Our findings illuminate the potential of Sn-based nanocrystals for optoelectronic applications.

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Energetic disorder dominates optical properties and recombination dynamics in tin-lead perovskite nanocrystals


Dandan Wang, Yusheng Li, Yongge Yang, Chao Ding, Yuyao Wei, Dong Liu, Hua Li, Huan Bi, Shikai Chen, Sujun Ji, Boyu Zhang, Yao Guo, Huiyun Wei, Hongshi Li, Shuzi Hayase, Qing Shen



Fig. Energetic disorder shapes optical and recombination behavior in tin-lead perovskite nanocrystals.


Tin-lead alloyed perovskite nanocrystals (PNCs) offer a promising pathway toward low-toxicity and air-stable light-emitting devices. However, substantial energetic disorder has thus far hindered their lighting applications compared to pure lead-based PNCs. A fundamental understanding of this disorder and its impact on optical properties is crucial for overcoming this limitation. Here, using temperature-dependent static and transient absorption spectroscopy, we meticulously distinguish the contributions of static disorder (including defects, impurities, etc.) and dynamic disorder (carrier-phonon interactions). We reveal how these disorders shape band-tail structure and ultimately influence inter-band carrier recombination behaviors. Surprisingly, we find that static and dynamic disorder primarily control band-tail defect states and bandgap renormalization, respectively, which together modulate fast carrier trapping and slow band-band recombination rates. Furthermore, we link these disorders to the tin-induced symmetry-lowering distortions in tin-lead alloyed PNCs. These findings illuminate critical design principles for highly luminescent, low-toxicity tin-lead PNCs, accelerating their adoption in optoelectronic applications.


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Over 15% Efficiency PbS Quantum-Dot Solar Cells by Synergistic Effects of Three Interface Engineering: Reducing Nonradiative Recombination and Balancing Charge Carrier Extraction

Chao Ding, Dandan Wang, Dong Liu, Hua Li, Yusheng Li, Shuzi Hayase, Tomah Sogabe, Taizo Masuda, Yong Zhou, Yingfang Yao, Zhigang Zou, Ruixiang Wang, Qing Shen



Fig. An innovative interface modification method developed for the three interfaces of a lead sulfide colloidal quantum dot solar cell allows precise control of the photogenerated carriers across the device, balancing carrier extraction while minimizing nonradiative recombination at each interface of the device, increasing carrier extraction efficiency at the maximum power point and power conversion efficiency by over 15%.


Lead sulfide colloidal quantum dot solar cells (CQDSCs), the next generation of photovoltaics, are hampered by non-radiative recombination induced by defects and an electron-hole extraction imbalance. CQDSCs have three interfaces: CQD/CQD, electron transport layer (ETL)/CQD, and CQD/hole transport layer (HTL), and modifying one of these interfaces does not fix the problem stated above. Here, coordinated control and passivation of the three interfaces in PbS CQDSCs are presented and it is shown that the synergistic effects may improve charge transport and charge carrier extraction balance and minimize non-radiative recombination simultaneously. A facile method is developed for epitaxially growing an ultrathin perovskite shell on the CQD surface to passivate the CQD/CQD interface, resulting in CQD absorber layers with long carrier diffusion lengths. With the introduction of organic films with adjustable electrical characteristics, the influence of ETL/CQD interfacial modifications on carrier transport and recombination is investigated. An excessive increase in the electron extraction rate reduces the fill factor and solar efficiency, as discovered. Therefore a modified layer is created at the CQD/HTL interface to promote hole extraction, which enhances charge extraction balance and passivates the interface. Finally, PbS CQDSCs exhibit a power conversion efficiency of 15.45%, a record for Pb chalcogenide CQDSCs.

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Stronger Coupling of Quantum Dots in Hole Transport Layer Through Intermediate Ligand Exchange to Enhance the Efficiency of PbS Quantum Dot Solar Cells


Yuyao Wei, Chao Ding, Guozheng Shi, Huan Bi, Yusheng Li, Hua Li, Dong Liu, Yongge Yang, Dandan Wang, Shikai Chen, Ruixiang Wang, Shuzi Hayase, Taizo Masuda, Qing Shen



Fig. To solve the problem of volume shrinkage and inhomogeneous energy landscape, a novel method for PbS-EDT HTL preparation using small-sized benzoic acid (BA) as intermediate ligands is proposed in this work. Stronger coupling between QDs and reduced defects in the QD HTL are realized. Nearly 20% growth in  Jsc and a 23.4% higher PCE of 13.2% are achieved.


Nowadays, the extensively used lead sulfide (PbS) quantum dot (QD) hole transport layer (HTL) relies on layer-by-layer method to replace long chain oleic acid (OA) ligands with short 1,2-ethanedithiol (EDT) ligands for preparation. However, the inevitable significant volume shrinkage caused by this traditional method will result in undesired cracks and disordered QD arrangement in the film, along with adverse increased defect density and inhomogeneous energy landscape. To solve the problem, a novel method for EDT passivated PbS QD (PbS-EDT) HTL preparation using small-sized benzoic acid (BA) as intermediate ligands is proposed in this work. BA is substituted for OA ligands in solution followed by ligand exchange with EDT layer by layer. With the new method, smoother PbS-EDT films with more ordered and closer QD packing are gained. It is demonstrated stronger coupling between QDs and reduced defects in the QD HTL owing to the intermediate BA ligand exchange. As a result, the suppressed nonradiative recombination and enhanced carrier mobility are achieved, contributing to ≈20% growth in short circuit current density (Jsc) and a 23.4% higher power conversion efficiency (PCE) of 13.2%. This work provides a general framework for layer-by-layer QD film manufacturing optimization.

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Enhanced Hot-Phonon Bottleneck Effect on Slowing Hot Carrier Cooling in Metal Halide Perovskite Quantum Dots with Alloyed A-Site


Hua Li Qing Wang Yusuke Oteki Chao Ding Dong Liu Yao Guo Yusheng Li Yuyao Wei Dandan Wang Yongge Yang Taizo Masuda Mengmeng Chen Zheng Zhang Tomah Sogabe Shuzi Hayase Yoshitaka Okada Satoshi Iikubo Qing Shen


Fig. The controversies regarding the origins and mechanisms of A-site cation-dependent hot carrier relaxation dynamics are resolved by comparing the photogenerated carrier dynamics of 6 kinds of pure and mixed A-site cation halide perovskite quantum dots (i.e., FAPbI3, MAPbI3, CsPbI3, FA0.5MA0.5PbI3, FA0.5Cs0.5PbI3, MA0.5Cs0.5PbI3 PQDs) at various excitation intensities.


A deep understanding of the effect of the A-site cation cross-exchange on the hot-carrier relaxation dynamics in perovskite quantum dots (PQDs) has profound implications on the further development of disruptive photovoltaic technologies. In this study, the hot carrier cooling kinetics of pure FAPbI3 (FA+, CH(NH2)2+), MAPbI3 (MA+, CH3NH3++), CsPbI3 (Cs+, Cesium) and alloyed FA0.5MA0.5PbI3, FA0.5Cs0.5PbI3, and MA0.5Cs0.5PbI3 QDs are investigated using ultrafast transient absorption (TA) spectroscopy. The lifetimes of the initial fast cooling stage (<1 ps) of all the organic cation-containing PQDs are shorter than those of the CsPbI3 QDs, as verified by the electron-phonon coupling strength extracted from the temperature-dependent photoluminescence spectra. The lifetimes of the slow cooling stage of the alloyed PQDs are longer under illumination greater than 1 sun, which is ascribed to the introduction of co-vibrational optical phonon modes in the alloyed PQDs. This facilitated efficient acoustic phonon upconversion and enhanced the hot-phonon bottleneck effect, as demonstrated by first-principles calculations.

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In Situ Room-Temperature Synthesis of All-Colloidal Quantum Dot CsPbBr3–PbS Heterostructures


Yongge Yang, Dandan Wang, Yusheng Li, Jing Xia, Huiyun Wei, Chao Ding, Yuyu Hu, Yuyao Wei, Hua Li, Dong Liu, Guozheng Shi, Yaohong Zhang, Huan Bi, Shikai Chen, Hongshi Li, Xiang-Min Meng, Shuzi Hayase, and Qing Shen



Fig. Under ambient conditions, we achieved the in-situ synthesis of CsPbBr3-PbS heterojunctions. The fundamental structure is illustrated in the above diagram on the left. PbS can in-situ grow on the surface of CsPbBr3 due to their minimal lattice mismatch. Simultaneously, owing to the chemical bonding at the heterojunction interface and the type-I energy level alignment, an exceptionally efficient charge carrier transfer process from CsPbBr3 to PbS occurs within the heterojunction, as depicted in the above diagram on the right.


In optoelectronics, all-colloidal quantum dot (all-CQD) heterostructures featuring processability and extending the functionalities of individual quantum dots (QDs) have garnered significant attention. Particularly, perovskite and chalcogenide QD heterostructures present a compelling platform for integrating visible- and near-infrared spectral responses through effective carrier transfer. However, a lack of controllable and low-cost synthesis methodologies currently curtails the development and application of such intricate structures. Herein, we report a facile and replicable in situ room-temperature synthesis approach for yielding spectrally tunable, low-cost processing all-CQD CsPbBr3–PbS heterostructures. This approach utilizes the controllable growth and high surface reactivity of amine-free CsPbBr3 QDs, together with a highly reactive sulfur source, to facilitate the in situ formation of heterostructures at room temperature. Our fabricated all-CQD CsPbBr3–PbS heterostructures possess excellent processability and showcase sustainable dual emission in both visible and infrared spectra. The control over which is finely tuned through the manipulation of the Pb/S ratio. Transient absorption spectroscopy reveals ultrafast interdot carrier injection (initiating in less than 1 ps) from the perovskite to PbS within the heterostructures, allowing the photons absorbed by CsPbBr3 QDs to be efficiently provided for PbS’s infrared emission. Based on their low-cost processability, we debuted their application in short-wave infrared imaging by harnessing ultraviolet light. We attained a resolution with a low response threshold of 18 mW/cm2 (365 nm), which approaches the International Electrotechnical Commission’s safety limit (10 mW/cm2), significantly surpassing the performance of standalone PbS QDs. Our research presents a reproducible technique for creating controllable and low-cost processing all-CQD heterostructures, which sets the stage for future developments in their application.


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Simultaneous Characterization of Optical, Electronic, and Thermal Properties of Perovskite Single Crystals Using a Photoacoustic Technique


Dong Liu, Hua Li, Yusheng Li, Taro Toyoda, Koji Miyazaki, Shuzi Hayase, Chao Ding, and Qing Shen



Fig. Acquisition of optical, electronic and thermal properties of perovskite single crystals by photoacoustic technique.


Metal halide perovskite possesses many excellent properties beneficial to its potential applications in optoelectronics and pyroelectricity. Surface recombination velocity, electronic diffusivity, and excess carrier lifetime accounting for the photoexcited carrier recombination and electronic transport features are key for improving the performance of perovskite-based optoelectronic devices. Meanwhile, the thermal conductivity and thermal diffusivity in halide perovskite have been paid limited attention despite their potential practical applications such as heat management and thermoelectric materials. To date, lots of techniques have been developed to extract these physical properties, while very few of them can effectively and nondestructively receive the results. The photoacoustic (PA) technique based on photothermal conversion is a powerful method to study the optical, electronic, and thermal properties of various materials, especially semiconductor materials. Optical absorption spectrum, surface recombination velocity, electronic diffusivity, photoexcited carrier lifetime, and thermal diffusivity can be obtained simultaneously without the destruction and contact of the samples. Here, for the first time, we utilized the PA technique in the perovskite single crystal. Optical absorption of MAPbBr3 and MAPbI3 (MA = methylammonium) single crystals was investigated under a reflection detection configuration (RDC), and the electronic and thermal properties were measured under a transmission detection configuration (TDC). Comparing the results with previous reports and other characterizations, the PA technique has been verified to be an efficient and convenient method to study the optical, electronic, and thermal properties of perovskite single crystals.

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