Research progress on stability enhancement of CsPbX3 perovskite and photovoltaic devices

The CsPbX₃ (X is halide anions) based all-inorganic perovskites are regarded to be one of the most appealing research hotspots among perovskite photovoltaics in the past few years, mainly due to their superior thermal stability compared to the organic-inorganic hybrid counterparts. At present, the highest photoelectric conversion efficiency of all-inorganic perovskite solar cells has reached 19.03%, which has good development potential. However, the Goldschmidt tolerance factor of this type of perovskite is close to the critical boundary value, which leads to phase instability. Accordingly, numerous works have been published on the stability enhancement of CsPbX₃ perovskite in recent years. This review summarizes the progress and strategies in the preparation of stable and efficient all-inorganic perovskite solar cells (PSCs), including the enlargement of tolerance factor, enhancement of activation energy barrier for phase transition (black phase to yellow phase), and decreasing the surface energy as well as modulation of the crystallization procedure. Finally, challenges and perspective of the future development of all-inorganic CsPbX₃ based PSCs are presented.     

CsPbX3钙钛矿材料与光伏器件稳定性强化研究进展

基于CsPbX₃(X为卤素阴离子)的全无机钙钛矿与含甲胺、甲脒等有机阳离子的有机-无机杂化钙钛矿相比,具有更优异的热稳定性,是近几年来钙钛矿光电领域最具吸引力的研究热点之一。目前全无机钙钛矿太阳电池的最高光电转换效率已经达到19.03%,具有很好的发展潜力。然而,这类钙钛矿材料的Goldschmidt容忍因子接近临界值,存在相不稳定的问题。近年来已经有相当多的研究聚焦于CsPbX₃钙钛矿材料与器件的稳定性强化工作。从增大容忍因子、提高相转变能垒、减小表面能、调控结晶过程等策略与方法入手,系统总结了近年来在制备稳定高效全无机CsPbX₃钙钛矿太阳能电池方面的进展,并对面临的挑战和未来的发展方向做出了展望。     

Lead-free double perovskite halide fluorescent oxygen sensor with high stability

Oxygen sensors, using organic-inorganic and all-inorganic lead halide perovskites, have demonstrated huge advantages in operating temperature, responding time, and reversing oxygen content detection. Nevertheless, the toxicity and instability issues hinder their wide application. In this work, for the first time, we report a sensitive fluorescence oxygen detector based on lead-free double perovskite Cs₂AgBiBr₆ thin film. The sensor has a remarkable performance in terms of fast response time of ≈56 s, recovery time of ≈91 s, and a relatively low limit of detection (LOD) of 150 ppm. More importantly, the unencapsulated sensor still exhibits an obvious response at low oxygen concentrations after two-week storage in ambient, and the device also exhibits good humidity, light, and thermal stability. Consequently, the lead-free double perovskite (Cs₂AgBiBr₆) will be promising environmentally friendly material in developing reversible, sensitive, high-efficiency, and stable perovskite oxygen sensors.     

Structural,optical, and electrical properties of tin iodide-based vacancy-ordered-double perovskites synthesized via mechanochemical reaction

Over the recent past, lead-based halide perovskite materials have drawn significant attention due to their excellent optical and electrical properties for solar cells and optoelectronics applications. However, the toxicity of lead elements and instability under ambient conditions leads to develop alternative compositions. Herein, we report a novel mechanochemical synthesis of tin iodide-based double perovskites (A₂SnI₆; A = Rb⁺, Cs⁺, methylammonium, and formamidinium), and their structural, optical, and electrical properties are investigated. Importantly, we found that the hydrogen iodide (HI) addition during the ball-milling process minimizes secondary phase formation in the synthesized A₂SnI₆ powders. The effects of HI addition and the A-site substitution are investigated with respect to the lattice parameters, optical bandgaps, and electrical properties of the synthesized perovskite materials. Our results demonstrate essential information to improve the understanding of halide perovskite materials and develop efficient lead-free perovskite photoelectric devices.     

Reproducible switching effect of an all-inorganic halide perovskite CsPbBr3 for memory applications

All-inorganic halide perovskite CsPbBr₃ have been developed and investigated. We have further demonstrated the using of this stable all-inorganic halide perovskite as storage media in memristors. Reproducible typical bipolar resistance switching behaviors in two different structures of resistance random access memory devices (Pt/CsPbBr₃/FTO and Pt/CsPbBr₃/Cu₂O/FTO) are observed. Particularly, the Pt/CsPbBr₃/Cu₂O/FTO device based on CsPbBr₃/Cu₂O heterojunction exhibits a remarkably high resistance switching effect with low set and reset voltages. Such appealing characteristics are comparable with those of frequently-used transition metal oxides perovskites like BaTiO₃ and SrZrO₃, etc. Possible conduction mechanisms are also proposed to understand the resistance switching behaviors of the studied devices.     

无铅铜基钙钛矿Cs2CuBr4的湿度传感性能

铅卤钙钛矿因其优异的光电性能引起了人们的极大关注,但由于其内在的不稳定性以及铅的毒性问题,限制了其实际应用。本文制得一种性能较稳定的无铅铜基钙钛矿Cs₂CuBr₄,利用其对湿度较为敏感的特性,创制了基于Cs₂CuBr₄敏感膜的石英晶体微天平（quartz crystal microbalance, QCM）湿度传感器。结果表明,当钙钛矿溶液的浓度小于0.4μg/μL时,敏感膜在11%~84%相对湿度下具有良好的湿度传感性能。其中最优浓度为0.3μg/μL（QCM-3）、薄膜质量398.95ng时,传感器具有高灵敏度（37.65Hz/% RH）,优异的对数线性关系（R²=0.9948）和快速的响应/恢复时间（5s/1s）。由此可见,无铅铜基钙钛矿Cs₂CuBr₄在湿度传感领域具有良好的应用前景。     

Vacuum-deposited perovskite CsPbBr3 thin-films for temperature-stable Si based pure-green all-inorganic light-emitting diodes

Metal halide perovskite light-emitting diodes (PeLEDs) are excellent candidates in the field of lighting and display due to their outstanding optical-electrical properties. However, the solution-processed technology of perovskite films and the organic electron/hole transport layers of PeLEDs make it still challenging to improve the operational stability of devices. Herein, we successfully prepared highly luminescent CsPbBr₃ perovskite films via vacuum-deposited method and then fabricated all-inorganic PeLEDs with the heterostructure of p-NiO/CsPbBr₃/n-Si. Our device exhibits pure-green emission with a wavelength of 527 nm, a narrow full width at half-maximum of 18 nm, and a maximum luminance of 51933 cd/m², representing one of the best brightness pure-green PeLEDs. Most importantly, the PeLEDs exhibited great thermal stability with a heat resistance up to 80 °C. The electroluminescence peak position of the PeLEDs remains consistent when the ambient temperature increases from 40 °C to 110 °C. Moreover, the all-inorganic PeLEDs can maintain their good luminescence performance after seven thermal cycling tests (30 °C–100 °C). This work not only demonstrated a facile strategy to prepare high-quality pure-green CsPbBr₃ perovskite films, but also provided an important all-inorganic device structure for high thermal stability of PeLED.     

Lead oxide enables lead volatilization pollution inhibition and phase purity modulation in perovskite quantum dots embedded borosilicate glass

Embedding all-inorganic cesium lead halide CsPbX₃ (X=Cl, Br, I) perovskite quantum dots (PQDs) PQDs into glass is one of the most effective strategies to improve their optical, thermal and chemical stabilities. Herein, by using PbO instead of PbBr₂ as the lead source, it is effective to lower the melting temperature and reduce the volatilization pollution from lead halide raw materials. Thus, a high-purity CsPbBr₃ PQDs embedded glass with 71.5 % PLQY was successfully prepared. The thermal stability, and photo-aging properties were also improved. By simply changing the halogen element, the red and blue CsPbX₃ PQDs embedded glasses were successfully prepared. The white LED fabricated by coating obtained green/red CsPbX₃ PQDs embedded glass on a blue chip displays high color gamut of 121.9 % NTSC standard and >91.1 % Rec. 2020 standard, which embodies the great potential of PQDs embedded glass in lighting and display fields.     

The hybrid halide perovskite: Synthesis strategies,fabrications, and modern applications

The organic–inorganic hybrid halide perovskite has several outstanding properties that are beneficial for optoelectronic and photovoltaic applications. Their interesting properties and the use in several modern application, attracted attention of the materials researchers. However, in this review, we describe how hybrid perovskite-based solar cells has become an important renewable source of energy along with historical background and the future of this potential material. We also describe the synthesis and fabrication methods for preparing ultrathin to bulk perovskites and their crystallographic nature of pure and mixed metallic hybrid perovskite system. This review not only focused on properties of hybrid perovskite but also represents the drawback as well as the development and performance in different fields of application.     

石墨炔及其衍生物在钙钛矿太阳能电池的应用

钙钛矿太阳能电池(PSCs)因具有高效率、可溶液加工和低成本等优点受到了人们广泛的关注。然而，在PSCs的各个功能层及界面之间存在缺陷非辐射复合、界面接触不良和薄膜质量较差等问题，阻碍了PSCs光电转换效率和稳定性的提高。相较于石墨烯，含有sp杂化碳原子的石墨炔具有独特的三角微观结构、天然的带隙、超高的载流子迁移率以及优异的光电和机械性能，成为光电能源领域重要的候选材料。综述了石墨炔及其衍生物在PSCs的电子传输层、空穴传输层以及光吸收层中的应用，重点探讨了石墨炔及其衍生物在功能层及其界面中钝化缺陷、改善薄膜形貌和界面接触、提高载流子传输等方面的作用。最后，对石墨炔及其衍生物在PSCs领域中的发展提出了展望。     

Construction of ultra‐stable perovskite–polymer fibre membranes by electrospinning technology and its application to light‐emitting diodes

Recently, organometallic halide perovskites have shown attractive application prospects in photoelectric devices depending on their excellent electro‐optic properties. However, their poor stability has greatly limited their practical applications. Here, methylammonium lead tribromide (MAPbBr₃) crystals are protected by polystyrene (PS) fibre membranes using electrospinning technology. The MAPbBr₃@PS composite fibre membranes fabricated in this work not only show strong photoluminescence properties but also excellent stability: 70% of the fluorescence intensity of MAPbBr₃@PS is maintained after soaking in water for 30 days, 85% after leaving at 95 °C for 350 min, and 90% after irradiating under UV light for 100 h. The excellent stability of the MAPbBr₃@PS fibre membranes may be attributed to the hydrogen bonds between the MAPbBr₃ crystal and the PS fibre. In addition, a high‐brightness white‐light‐emitting diode based on MAPbBr₃@PS fibre was fabricated, which fully demonstrates its application prospects in the field of colour conversion. © 2020 Society of Industrial Chemistry     

Enhanced power conversion efficiency of perovskite solar cells using dopant-free carbon nanotubes-Spiro-OMeTAD

Paintable carbon-based perovskite solar cells (PSCs) are of tremendous attention due to their structural stability and low fabrication cost. However, the poor interfacial contact and unsatisfied energy band alignment between carbon and perovskite lead to relatively low efficiency of carbon-based perovskite solar cells. Herein, we employed a multi-functional holes transfer layer, a dopant-free Spiro-OMeTAD composited with CNTs (CNTs-spiro), to bridge the interface between carbon and perovskite and optimize the energy band alignment in carbon-based PSCs. The power conversion efficiency of the PSCs with the CNTs-spiro layer (10.45%) has an enhancement of 17.51% compared with the PSC without the CNTs-spiro layer (8.62%). Our non-encapsulated devices showed excellent stability under light, air, or ambient conditions. The CNTs-spiro composition may be a promising hole transfer material for PSCs with high efficiency and high stability.     

Sodium bismuth titanate-based lead-free RAINBOW piezoelectric devices

The piezoelectric properties of lead-free piezoelectric ceramics are normally lower than those of lead oxide-based ceramics. In order to enhance the electromechanical performance of lead-free piezoelectric ceramics, an asymmetric chemical reduction was applied to sodium bismuth titanate (NBT)-based piezoelectric ceramics. Similar to the lead-containing ceramics, a curvature structure can be induced by the reduction in the NBT-based materials and lead-free RAINBOW (reduced and internally biased oxide wafer) devices can be fabricated. A large displacement (approximately 17 μm) under an electric field of 900 V/mm and high piezoelectric sensitivity (>4000 pC/N) under a stress, which are related to the reduction induced curvature, can be measured in the NBT-based devices. The apparent piezoelectric response of the lead-free RAINBOW devices is comparable to that of Pb(Zr,Ti)O₃-based devices. We proposed that apart from the piezoelectric properties, flexoelectric effect could also be a contributing mechanism for the observed apparent piezoelectric response in RAINBOW devices.     

Synthesis,characterization and photovoltaic properties of two-dimensional conjugated polybenzodithiophene derivatives appending diketopyrrolopyrrole units as side chain

Two side-chain donor-acceptor (D-A) narrow-band-gap two-dimensional (2D) conjugated polymers of POBDTDPPs and PTBDTDPPs with benzodithiophene (BDT) as D unit and appending diketopyrrolopyrrole (DPP) as A unit were designed and synthesized. The optical, thermal, electrochemical and photovoltaic properties have been investigated. It was found that both polymers exhibit better solution processability and a deeper HOMO energy level relative to its corresponding main-chain conjugated polymers (PBDT-DPP). Moreover, the PTBDTDPPs with an additional di(alkylthiophene)- substituted BDT unit shows a deeper HOMO energy level than the POBDTDPPs with a dialkoxy- substituted BDT unit. Using PTBDTDPPs as an electron donor and [6,6]-phenyl-C₇₁-butyric acid methyl ester as an electron acceptor, the resulting polymer solar cells (PSCs) exhibited meliorative photovoltaic properties with a power conversion efficiency (PCE) of 2.92% and open circuit voltage (V_oc) of 0.94 V. The PCE and V_oc levels are 1.52–2.92 and 1.14–1.18 times higher than those in the PBDT-DPP- and POBDTDPPs-based PSCs, respectively. This work demonstrates a good example for tuning energy level and photovoltaic properties of the polymers by the application of 2D conjugated structure.     

Tin and germanium monochalcogenide IV-VI semiconductor nanocrystals for use in solar cells

The incorporation of colloidal semiconductor nanocrystals into the photoabsorbant material of photovoltaic devices may reduce the production costs of solar cells since nanocrystals can be readily synthesized on a large scale and are solution processable. While the lead chalcogenide IV-VI nanocrystals have been widely studied in a variety of photovoltaic devices, concerns over the toxicity of lead have motivated the exploration of less toxic materials. This has led to the exploration of tin and germanium monochalcogenide IV-VI semiconductors, both of which are made up of earth abundant elements and possess properties similar to the lead chalcogenides. This feature article highlights recent efforts made towards achieving synthetic control over nanocrystal size and morphology of the non-lead containing IV-VI monochalcogenides (i.e., SnS, SnSe, SnTe, GeS and GeSe) and their application toward photovoltaic devices.     

Nanocrystallization of lead-free Cs3Sb2Br9 perovskites in chalcogenide glass

Lead-free halide perovskite nanocrystals (HPNCs) are an emergent alternative of lead-based halide perovskites owing to their environmentally benign nature. In this work, lead-free Cs₃Sb₂Br₉ HPNCs were precipitated firstly in chalcogenide glass through an elaborated composition design and appropriate crystallization process. The microstructural evolution and nanocrystallization behavior of the Cs₃Sb₂Br₉ crystallized glass-ceramics were analyzed by employing advanced characterization techniques. It is revealed that the crystallization process is temperature-dependent and can be described as two stages. At the first crystallization stage, the nucleation and crystal growth of Cs₃Sb₂Br₉ HPNCs occur due to the presence of structural similarity of [Sb₂Br₉]³⁻ dioctahedral clusters in the precursor glass. And then the second crystalline phase of GeS₂ is successively separated from the residual glassy matrix under high-temperature treatment. This work should be of great guiding significance for developing novel glass-ceramic materials embedded with lead-free HPNCs.     

Nanotetrapods: quantum dot hybrid for bulk heterojunction solar cells

Hybrid thin film solar cell based on all-inorganic nanoparticles is a new member in the family of photovoltaic devices. In this work, a novel and performance-efficient inorganic hybrid nanostructure with continuous charge transportation and collection channels is demonstrated by introducing CdTe nanotetropods (NTs) and CdSe quantum dots (QDs). Hybrid morphology is characterized, demonstrating an interpenetration and compacted contact of NTs and QDs. Electrical measurements show enhanced charge transfer at the hybrid bulk heterojunction interface of NTs and QDs after ligand exchange which accordingly improves the performance of solar cells. Photovoltaic and light response tests exhibit a combined optic-electric contribution from both CdTe NTs and CdSe QDs through a formation of interpercolation in morphology as well as a type II energy level distribution. The NT and QD hybrid bulk heterojunction is applicable and promising in other highly efficient photovoltaic materials such as PbS QDs.     

太阳能电池无铅导电电极的制备及电性能研究

以Bi2O3、B2O3和SiO2为主要原料制备无铅玻璃粘合剂,将其与导电银(Ag)粉、Al2O3、MnO2等无机添加剂和α-松油醇等有机载体进行混合制备无铅导电银浆,在800℃的温度下烧结20s形成Ag电极。采用四点探针法测量Ag电极电阻率ρ,通过SEM观察其断面形貌并用Keithley2400数字源表测定电池的相关性能参数,研究了Ag电极中导电Ag粉含量对电极性能的影响,确定了无铅导电Ag浆的质量配比为:导电银粉75%,玻璃粘合剂(Glass frit,GF)4%,无机添加剂1%,有机载体20%时,Ag电极的电性能趋于最佳。     

Antiperovskite Sr3MN and Ba3MN (M = Sb or Bi) as promising photovoltaic absorbers for thin-film solar cells: A first-principles study

Although lead halide perovskites (LHPs) have emerged as interesting photovoltaic (PV) absorbers for thin-film solar cells, the toxicity of Pb and poor materials stability have hindered the commercialization of solar cells using LHPs. Herein, using density functional theory (DFT) calculations, we suggest antiperovskite nitrides Sr₃MN and Ba₃MN (M = Sb or Bi) as potential Pb-free PV absorbers for thin-film solar cells. State-of-the-art DFT calculations based on the GW approximation show that these compounds have direct bandgaps suitable for PV applications. In addition, they exhibit significant absorption coefficients over 10⁵ cm⁻¹ for the visible light. By calculating spectroscopic limited maximum efficiency, we demonstrate that the film thicknesses of several hundred nanometers are enough for Sr₃MN and Ba₃MN to generate high-power conversion efficiencies over 20%. The analysis of the electron and hole effective masses reveals that these compounds have efficient carrier-diffusion paths allowing for the facile extraction of photocarriers. Lastly, we investigate the band alignments of the materials to help the design of thin-film solar cells.     

Enhancing light harvesting in planar halide perovskite film solar cells by silicon nanorods

The introduction of nanostructures is an effective method to boost the photovoltaic performance of hybridized organic-inorganic halide perovskite-film solar cells. Taking into account their excellent light-scattering in the ultraviolet–visible range and their chemical inertness, silicon (Si) nanorods can be incorporated into the perovskite-film solar cells to enhance the light harvesting of the devices. By depositing Si nanorods between the prepared film and the substrate, the light scattering induced by the Si nanorods significantly promoted light absorption of the films. Moreover, resulting from the incorporation of Si nanorods, the enlarged grain size and compact structure of the films prolonged the lifetime of the carriers, which promoted the photoelectric properties of the perovskite films. By the appropriate incorporation of Si nanorods, the photovoltaic conversion efficiency of the CH₃NH₃Pb(Br_0.25I_0.75)₃-film-based solar cell was increased from 12.6% to 14.9% and the relative stability of the devices under dark humidity was improved. This strategy of employing low-cost and easily prepared Si nanorods to enhance the light harvesting of perovskite photovoltaic devices could be applied to photovoltaic devices based on perovskite films with other compositions.