Formamidinium Lead Bromide (FAPbBr_3) Perovskite Microcrystals for Sensitive and Fast Photodetectors

Because of the good thermal stability and superior carrier transport characteristics of formamidinium lead trihalide perovskite HC(NH_2)_2 PbX_3(FAPbX_3), it has been considered to be a better optoelectronic material than conventional CH_3NH_3-PbX_3(MAPbX_3). Herein, we fabricated a FAPbBr_3 microcrystal-based photodetector that exhibited a good responsivity of 4000 A W-1 and external quantum efficiency up to 106% under one-photon excitation, corresponding to the detectivity greater than 1014 Jones. The responsivity is two orders of magnitude higher than that of previously reported formamidinium perovskite photodetectors. Furthermore, the FAPbBr_3 photodetector's responsivity to two-photon absorption with an 800-nm excitation source can reach 0.07 A W^(-1), which is four orders of magnitude higher than that of its MAPbBr_3 counterparts. The response time of this photodetector is less than 1 ms.This study provides solid evidence that FAPbBr_3 can be an excellent candidate for highly sensitive and fast photodetectors.

CuInSe_(2)/CuInS_(2)Ⅱ型核壳结构量子点的构建及高效光电化学电池

环保型CuInSe_(2)量子点具有高消光系数和宽光谱吸收范围,在光电化学催化应用中展现了良好的发展前景.然而,CuInSe_(2)量子点较低的载流子分离能力和严重的界面电荷复合降低了其光电化学性能,制约了其应用.因此,我们设计并合成了具有Ⅱ型能带排列的CuInSe_(2)/CuInS_(2)核/壳结构量子点,以促进载流子分离、减少界面缺陷;进一步通过调节In/Cu前驱体的摩尔比,产生铜空位.光物理性质研究表明,导带电子-铜空位捕获的空穴之间的辐射复合成为主要的复合方式,有效延长了载流子寿命,促进了载流子分离.因此,基于富铜空位的CuInSe_(2)/CuInS_(2)核壳量子点的光阳极获得了~8.0 mA cm^(-2)的最大饱和光电流密度,该性能是当前报道的CISe基量子点光电化学电池中的最高值之一.本工作提供了一种通过表面或内在缺陷的调控来促进光电化学应用中的电荷载流子分离和传输的有效方法.

采用高导热金刚石基底的高效散热钙钛矿激光

具有低温升的高效散热方案是实现电泵浦激光的关键因素之一.高导热金刚石有望克服钙钛矿激光的散热限制.本文中,我们展示了一种可以将光泵浦过程中产生热量高效耗散的金刚石基底钙钛矿纳米片激光.此外,紧密光学束缚可以通过在纳米片和金刚石基底之间引入一层薄SiO_(2)间隔层而实现.该激光的品质因子高达~1962,激光阈值为52.19μJ cm^(-2).受益于金刚石基底,其泵浦能量密度相关温度灵敏度较低(~0.56±0.01 K cm~2μJ^(-1)).本工作有望促进电泵浦钙钛矿激光的发展.

高稳定性铋基钙钛矿纳米晶的可控合成:结构和光物理性质

铋基钙钛矿因毒性低成为铅基钙钛矿的潜在替代品.目前,对铋基钙钛矿纳米晶的化学组成、晶体结构以及光物理过程的研究还缺乏系统性.特别地,紫外-可见吸收光谱和激发态载流子动力学,在已发表的论文中存在相当大的争议.在本文中,我们通过热注入法成功地合成了纯相的Cs_(3)BiBr_(6)和Cs_(3)Bi_(2)Br_(9)纳米晶,并通过调节热注入的温度来精确控制二者的化学组成和结构.在此基础上,系统研究了不同形貌和不同尺寸的Cs_(3)Bi_(2)Br_(9)纳米晶的紫外-可见吸收光谱,澄清了在这方面存在的争议.采用飞秒瞬态吸收光谱系统研究了Cs_(3)Bi_(2)Br_(9)纳米晶的激发态载流子动力学,结果表明载流子在被激发后的3 ps内会发生一个自捕获过程.与配体辅助再沉积法相比,用热注入法制备的Cs_(3)Bi_(2)Br_(9)纳米晶具有更好的光稳定性.基于Cs_(3)Bi_(2)Br_(9)纳米晶的光电探测器具有灵敏的光响应,显示出其在光电探测方面的应用潜力.

Inorganic ligands-mediated hole attraction and surface structural reorganization in InP/ZnS QD photocatalysts studied via ultrafast visible and midinfrared spectroscopies

Photoinduced carrier dynamical processes dominate the optical excitation properties of photocatalysts and further determine the photocatalytic performance.In addition,as the electrons generally possess a faster transfer rate than holes,hole transfer and accumulation are critical,and they play the key efficiency-limiting step during the photocatalytic process.Therefore,a comprehensive understanding of the dynamics of photogenerated holes and their determining factors in the photocatalytic system is highly essential to rationalize the full catalytic mechanism and develop highly efficient photocatalysts,which have not yet been revealed.In this work,the photoinduced charge carrier dynamics in InP/ZnS quantum dots(QDs)capped with longchain L-typed ligands(oleylamine)and inorganic ligands(sulfide ion(S^(2-)))were explored.Time-resolved photoluminescence and femtosecond transient-absorption spectroscopy unambiguously confirmed the ultrafast hole transfer from the InP core to S^(2-)ligands.Moreover,by probing the bleach of vibrational stretching of the ligands with transient midinfrared absorption spectroscopy,the hole transfer time was determined to be 4.2 ps.The injected holes are long-lived at the S^(2-) ligands(>4.5 ns),and they can remove electrostatically attached surfactants to compensate for the spatial charge redistribution.Finally,compared with other inorganic ligands such as Cl^(-) and PO_(4)^(3-),S^(2-) balances the ionic radii and net charge to ensure the optimal condition for charge transfer.Such observation rationalizes the excellent photocatalytic H_(2) evolution(213.6μmol mg^(-1) within 10 h)in InP/ZnS QDs capped with S^(2-) compared with those capped with other ligands and elucidates the role of surface ligands in the photocatalytic activity of colloidal QDs.

Microscopic morphology independence in linear absorption cross-section of CsPbBr_(3)nanocrystals

Multiple morphologies of colloidal perovskite nanocrystals(NCs)diversify their optical and electronic properties.Among them,the linear absorption cross-section(σ)is a primary parameter to determine their intrinsic photophysical features,and consequently,application potential.Herein,three morphologies of all-inorganic hybrid colloidal perovskite CsPbBr_(3)NCs,nanocubes(NBs),nanoplatelets(NLs),and nanowires(NWs),were targeted,and their linearσvalues were obtained through femtosecond transient absorption(TA)spectroscopy analysis.At high excitation energy well above the bandgap,theσper particle of all CsPbBr3 NCs linearly increased with the particle volume(VNC)regardless of the morphology with the value ofσ400=9.45×10^(4)cm^(−1)×VNC(cm^(2)).Density functional theory(DFT)calculation confirmed the negligible influence of shapes on the optical selection rules.The Einstein spontaneous emission coefficients calculated from theσvalues define the intrinsic radiative recombination rate.However,reduced size dependence is observed when the excitation energy is close to the bandgap(i.e.,at 460 nm)with the value ofσ460=2.82×10^(8)cm0.65×(VNC)0.45(cm^(2)).This should be ascribed to the discrete energy levels as well as lower density of states close to the band edge for perovskite NCs.These results provide in-depth insight into the optical characteristics for perovskite NCs.

Preface to the SPECIAL ISSUE: Excitonic Solar Cells(II)

Among all the excitonic solar cells(ESCs)including dyesensitized solar cells(DSSCs),quantum solar cells(QDSCs),perovskites solar cells(PSCs),and organic photovoltaics(OPVs),PSCs attracted enormous research attention in the past 7 years and attained the highest power conversion efficiency(PCE)of over 20%with the biggest progress,from 3.8%to over 22.1%in 7 years.However,one can easily realize the fact that such a rapid progress achieved in PSCs was made possible is largely based on the fundamental knowledge,experimental skills,and characterization facilities obtained and accumulated through the multi-decade long endeavor in the study of other excitonic solar cells.Even though PSCs have attractedmuch research human resource and funding,the study on other excitonic solar cells has never stopped,and such persistent

Ultrafast photoinduced dynamics in quantum dot-based systems for light harvesting

Colloidal semiconductor nanocrystals, referred to as quantum dots, offer simple low-temperature solution-based methods for constructing optoelectronic devices such as light emitting diodes and solar cells. We review recent progress in the understanding of photoinduced processes in key components of a certain type of quantum dot solar cells where the dots sensitize a suitable metal oxide, such as ZnO or TiO2, for electron injection, and NiO for hole injection. The electron and hole injection dynamics are discussed in detail as a function of the quantum dot size and core-shell structure, the linker molecule type, and the morphology of the accepting metal oxide. Hole trapping is identified as a major factor limiting the performance of quantum dot-based devices. We review possible strategies for improvement that use core-shell structures and directed excitation energy transfer between quantum dots. Finally, the generation and injection of multiple excitons are revisited. We show that the assumption of a linear relationship between the intensity of transient absorption signal and the number of excitons does not generally hold, and this observation can partially explain highly disparate results for the effidency of generating multiple exdtons. A consistent calculation procedure for studies of multiple exciton generation is provided. Finally we offer a brief personal outlook on the topic.

Preface to the SPECI AL ISSUE: Excitonic Solar Cells(Ⅰ)

Search and development of clean sustainable energy or renewable energy become an imperative demand beyond the concerns of limited resource and cost of fossil fuels that our modern life is so much dependent on.Among all the renewable energy,solar energy is the most abundant and likely to make the most significant contribution to the clean energy efforts.Although the usage of solar energy has