hujiao

Perovskite solar cells, bearing the merits of facile preparaion and remarkable efficiency, has great potential for bringing the photovoltaic industry to a new generation. The photovoltaic market demands high-efficiency, high stability and low-cost fabrication of perovksite solar cells, especially stability to the humid environment for operation. Here, MAPbI₃/agarose photoactive material for humid stable unencapsulated devices has been proposed. These solar cells have been operated in ambient humid environment without glove box, exhibiting efficiency up to 14.66% and retain 90% of its PCE after 1392 h and 60% of initial PCE after 1972 h in ambient humid environment (RH>70%) without encapsulation. FTIR and XPS measurements reveal two critical factors for the improved stability. The molecular level interactions between agarose and MAPbI₃ passivates the grain boundaries of perovskite thus preventing its degradation. Moreover, the formation of Li⁺-agarose complex at the interface between perovskite layer and hole conductive layer, effectively prevents the water uptake of MAPbI₃ layer. Both effects of passivation and minimization of hygroscopicity of LiTFSI by agarose lower the decomposition speed of perovskite, which obviously increases the power efficiency and stability of device.

Organometal lead halides perovskites are promising solar cells material due to their outstanding properties such as tuneable bandgap, impressive tolerance to defects, long exciton diffusion length, high carrier mobility and absorption coefficient. Up to now, the organometal lead halides based solar cells (PSCs) have demonstrated impressive power conversion efficiency reaching 25.2% (not stabilised). However, their operating life-times are limited due to degradation of the organic components under some environmental conditions. Therefore, researchers have focused their interest on the all inorganic perovskite; especially on the caesium lead triiodide perovskite (CsPbI₃) which exhibits a better compositional and chemical stability. Nevertheless, the phase instability of the black phase of this material constitutes its main limitation for its use in the solar cell devices production. This review aims to present the most impactful research giving insights on the factors that may cause the instability of all-inorganic lead halide perovskite materials, as well as the instability of the whole device. In addition to deposition methods, the composition, structure and optical properties of inorganic perovskite materials have also been presented. Furthermore, this review highlights the different strategies used in order to improve the phase stability of caesium lead halide perovskite material through either engineering on the material structure or the fabrication method.

Inverted perovskite solar cells (PSCs) have attracted tremendous attention recently but the energy levels between the perovskite absorber and conventional hole transport layers (HTL) are mismatch, resulting in the lower open-circuit voltages (V_oc) than that of regular PSCs. Herein, a gradient heterojunction (GHJ) based on poly(3,4−ethylenedioxythiophene: polystyrenesulphonate) (PEDOT:PSS)/PEDOT:PSS-VO_x was constructed in situ by low-temperature annealing and used as HTL of the inverted PSCs. This GHJ structure fabricated conveniently by doping a small amount of triisopropoxyvanadium oxide isopropyl alcohol solution into the PEDOT:PSS solution during spin-coating can efficiently facilitate charge separation and improve charge extraction efficiency, leading to significantly improved PSC performance with V_oc up to 1.02 V and power conversion efficiency (PCE) to 18.0%. More impressively, owing to the more hydrophobic surface and lower acidity than the PEDOT:PSS layer after the formation of high work function VO_x mainly on the surface of HTL, the GHJ-based PSCs show excellent long-term stability, which retain over 80% or 70% of their initial PCEs after exposure to full spectrum illumination in N₂ for 750 h or in air for 175 h, respectively. These results illustrate the significant advantages of the in situ formed VO_x-modified HTLs in gradient structures using organic VO_x precursors, providing important clues in constructing GHJ for inverted PSCs with high efficiency and stability.

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 NiO_x. 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/NiO_x, 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.

Organic-inorganic hybrid perovskites have potential applications in flexible electronics based on solution-processing polycrystalline thin-films. This article reports an emerging phenomenon: mechanically tunable spin-orbit coupling (SOC) in flexible perovskite solar cells under elastic bending. Polarization-dependent photocurrent studies show that mechanical bending increases the orbit-orbit interaction, shown as an enhanced SOC, and consequently boosting the intersystem crossing to convert optically generated bright states (which are allowed to recombine) into dark states (which are forbidden to recombine) in flexible perovskite solar cells [PET/ITO/PEDOT:PSS/MAPbI_3-xCl_x/PCBM/PEI/Ag]. Simultaneously, the photocurrent is increased from 15.39 mA/cm² to 22.0 mA/cm² by 43 % upon such elastic bending with the curvature radius of 4.2 mm. It is further found that introducing mechanical stress leads to both grain boundary interaction and grain deformation shown as the decreased defects at grain boundaries through thermal admittance spectroscopy and the elastic strain verified by X-ray diffraction measurement. The capacitance-frequency characteristics indicate that applying this mechanical stress causes an increase on the bulk polarization by introducing grain boundary interaction and grain deformation. This provides necessary condition to realize mechanically tunable SOC effects in perovskites via electric-magnetic coupling. Essentially, mechanically tunable SOC effects present new mechanisms to control the optoelectronic properties in flexible perovskite electronic devices.

White light emitting diodes (WLEDs) based on all-inorganic halide (CsPbX₃, X = Cl, Br and I) perovskite quantum dots (QDs) have attracted broad attention due to their high brightness. However, their poor stability and anion-exchange reaction when utilized together are still the main challenges that impede their applications. Herein, a one-step in situ method under room temperature in air is proposed to synthesize CsPbBr₃ QDs coated with SiO₂ (CsPbBr₃@SiO₂), where the whole process takes only 20 s. The as-prepared CsPbBr₃@SiO₂ QDs samples present an enhanced stability in the thermal and polar-solvent environment, maintaining its high photoluminescence quantum yield (PLQY~75%). Thereby WLEDs are constructed by combining CsPbBr₃@SiO₂ with red Ag–In–Zn–S QDs on InGaN blue chip, achieving a high color rendering index (CRI) of 91, a correlated color temperature (CCT) of 3689 K and a power efficiency of 40.6 lm W⁻¹.

All-inorganic cesium lead bromide (CsPbBr₃) perovskite solar cell is one promising candidate to balance high efficiency and poor stability of organic-inorganic hybrid photovoltaics. The charge carrier transport can be maximized for high-efficiency devices through precise stress control during perovskite grain growth process to obtain high-quality full-bromine CsPbBr₃ halide films. We present here the monolayer-aligned and large-grained CsPbBr₃ perovskite films through precise control of crystallization temperature of PbBr₂ film because the lattice volume is enlarged by 2.18 times during the phase conversion from PbBr₂ to CsPbBr₃, which helps to minimize residual-stress-induced grain boundaries and defect-induced charge recombination. Upon further interfacial modification by nitrogen doped carbon quantum dots, the hole transporting materials free, all-inorganic CsPbBr₃ perovskite solar cell achieves a champion efficiency as high as 10.71% with an ultrahigh open-circuit voltage of 1.622 V. Moreover, the unencapsulated solar cell demonstrates remarkable long-term stability in 85% humidity in air atmosphere.

An optimized bulk heterojunction (BHJ) interface, certifying enhanced exciton-splitting, charge separation and recombination inhibition, is vastly desired to obtain high power conversion efficiencies (PCEs). Herein, the ternary strategy has been employed to effectively modify the phase separation between the J71:ITIC blend by incorporating a 3D aggregation-induced emission (AIE) material, Tetraphenylethylene (TPE). Hence, as a consequence of improved charge mobility, lower bimolecular recombination and enhanced fill factor (FF), an excellent PCE of 12.16% has been achieved; a 21.23% increment over the PCE of binary devices. Likewise, Flory-Huggins parameter (χ) and surface free energy analysis reveals a high degree of miscibility between J71 and TPE, that leads to a rearrangement at the D-A interface such that TPE settles in between the D and A and thus forces the ITIC away from J71 and out of the mixed phase, indicating relatively higher average acceptor domain purity at the interface and ultimately better FF and PCE for the ternary devices. Likewise, TPE inclusion in various other fullerene and nonfullerene systems also leads to similar results, signifying this to be an effective methodology to boost the PCEs of the organic solar cells, especially for the systems with low FF.

Perovskite solar cells (PSCs) have emerged as a promising class of photovoltaic devices since they combine the benefits of high efficiency beyond 20%, low material cost, as well as easy and scalable processing. The appropriate choice of the electron transport layer (ETL) in these devices is one crucial aspect for achieving high efficient PSCs. The conventional ETL TiO₂ is not the best choice due to its relatively low conductivity and problematic photocatalytic activity. Therefore, novel ETLs have attained increasing attention and are making rapid progress and with it the further development and optimization of planar PSCs has been promoted. In this review, we start by introducing the essential functions of ETLs in planar PSCs. Next, we give an extensive description of novel ETL materials, looking at both crystalline and amorphous systems. Their emergence, development, and accompanying optimization strategies will be discussed. Additionally, we provide a brief discussion about the correlation between materials, fabrication methods, and interface related issues. In the end, we propose some prospective research subjects that will be relevant for the further development of novel ETLs.

Despite the remarkable photovoltaic characteristics and printability of perovskite solar cells, their intrinsic instability has been the most serious drawback toward future commercialization. In this work, we have investigated the stability of perovskite films in terms of morphology, electronic properties and chemical compositions. Specifically, the chemical decomposition inhibition strategy was introduced in perovskite films through iodine bromide to modify the crystal defects, leading to PSCs with suppressed hysteresis effects, superior durability and attractive PCE of 21.5%. Femto-second transient absorption spectra and GIWAXS measurements provide deep insight into the reduced carrier recombination and indicate the improved crystallinity of the modified perovskite films. Furthermore, an efficient hole-transporting material, PDPP4T, without using any doping process is applied to achieve PSCs with enhanced open-circuit voltage and better repeatability. As a consequence, the modified PSCs could maintain 82% of their initial efficiency after 5000 h of storage in ambient conditions and 90% of their initial efficiency after 1000 h of light soaking process. An excellent water resistance up to 100 h of the PSCs is also obtained by encapsulation technology. Besides, after coating Ce³⁺-CsPbI₃ nanocrystals as luminescent down-shifting layers on the front side of the PSCs, the PCE of the device was further improved to 22.16%.

BaZrS₃ is a prototypical chalcogenide perovskite, an emerging class of unconventional semiconductor. Recent results on powder samples reveal that it is a material with a direct band gap of 1.7–1.8 eV, a very strong light-matter interaction, and a high chemical stability. Due to the lack of quality thin films, however, many fundamental properties of chalcogenide perovskites remain unknown, hindering their applications in optoelectronics. Here we report the fabrication of BaZrS₃ thin films, by sulfurization of oxide films deposited by pulsed laser deposition. We show that these films are n-type with carrier densities in the range of 10¹⁹-10²⁰ cm⁻³. Depending on the processing temperature, the Hall mobility ranges from 2.1 to 13.7 cm²/Vs. The absorption coefficient is > 10⁵ cm⁻¹ at photon energy >1.97 eV. Temperature dependent conductivity measurements suggest shallow donor levels. By assuring that BaZrS₃ is a promising candidate, these results potentially unleash the family of chalcogenide perovskites for optoelectronics such as photodetectors, photovoltaics, and light emitting diodes.

The ionic defects in hybrid halide perovskite materials served as the recombination center severely restricts its application for solar cells. Here, we proposed a dual-passivation strategy via simply incorporating low-cost ammonium chloride to simultaneously passivate negative- and positive-charged ionic defects, as indicated by first-principles density functional theory calculation. The efficient defect modulation reduces the defect density and prolongs the carrier lifetime, thereby contributing to the highly crystalline perovskite, which is demonstrated by light-dependent kelvin probe force microscopy, transient absorption and visualized fluorescence lifetime imaging microscopy. Benefiting from these merits, the power conversion efficiency of perovskite solar cells is boosted up to 21.38%. More importantly, this dual-passivation approach can be further extended to mixed-cation perovskite systems, not limited in traditional methylammonium based perovskite only. Such methodology of simultaneously regulating ionic defects in different types may probably give impetus to effectively promote perovskite evolution.

In this work, we report on the design principles of high-power perovskite solar cells (PSCs) for low-intensity indoor light applications, with a particular focus on the electron transport layers (ETLs). It was found that the mechanism of power generation of PSCs under low-intensity LED and halogen lights is surprisingly different compared to the 1 Sun standard test condition (STC). Although a higher power conversion efficiency (PCE) was obtained from the PSC based on mesoporous-TiO₂ (m-TiO₂) under STC, compared to the compact-TiO₂ (c-TiO₂) PSC, c-TiO₂ PSCs generated higher power than m-TiO₂ PSCs under low-intensity (200–1600 Lux) conditions. This result indicates that high PCE at STC cannot guarantee a reliable high-power output of PSCs under low-intensity conditions. Based on the systemic characterization of the ideality factor, charge recombination, trap density, and charge-separation, it was revealed that interfacial charge traps or defects at the electron transport layer/perovskite have a critical impact on the resulting power density of PSC under weak light conditions. Based on Suns-V_OC measurements with local ideality factor analyses, it was proved that the trap states cause non-ideal behavior of PSCs under low-intensity light conditions. This is due to the additional trap states that are present at the m-TiO₂/perovskite interface, as confirmed by trap-density measurements. Based on Kelvin probe force microscopy (KPFM) measurements, it was confirmed that these traps prohibit efficient charge separation at the perovskite grain boundaries when the light intensity is weak. According to these observations, it is suggested that for the fabrication of high-power PSCs under low-intensity indoor light, the interface trap density should be lower than the excess carrier density to fill the traps at the perovskite's grain boundaries. Finally, using the suggested principle, we succeeded in demonstrating high-performance PSCs by employing an organic ETL, yielding maximum power densities up to 12.36 (56.43), 28.03 (100.97), 63.79 (187.67), and 147.74 (376.85) μW/cm² under 200, 400, 800, and 1600 Lux LED (halogen) illumination which are among the highest values for indoor low-intensity-light solar cells.

All-inorganic perovskites have drawn tremendous attentions in view of their superb thermal stability. However, unavoidable defects near the perovskite surface seriously hampers carrier transport and easily results in ion accumulation at the interface of perovskite layer and charge transport layer. Herein, delocalized thiazole and imidazole derivatives iodide salts functionalized on perovskite surface have been investigated comprehensively. These two salts post-treatment on perovskite could efficiently passivate traps arising from Cs⁺ or I⁻ vacancies. Additionally, these highly п-conjugated delocalized molecules can contribute to the efficient charge transport and prevent ions accumulation at the interface. As a result, sulfur-contained aminothiazolium iodide (ATI) post-treated CsPbI₂Br devices showed simultaneous enhanced current density and voltage due to its higher interaction with perovskite lattice, this led to a champion efficiency of 13.91% with superb fill factor of more than 80%, which exhibited dramatic enhancement compared with the control samples (10.12%). Furthermore, surface passivation with delocalized molecules could effectively stabilize CsPbI₂Br phase at room temperature or 80 °C annealing in ambient condition (65% RH). Equally important, this surface passivation allowed competitive efficiency of 11.26% with a large-area device (1.00 cm²). This high kill tolerant approach provide a new route to fabricate inorganic perovskite devices with higher efficiency and stability.