Search

Cu2ZnSn(S,Se)4 (CZTSSe) photovoltaic (PV) technology has attracted much attention due to its cost efficiency, non-toxic nature, and use of earth-abundant elements.

Transmission electron microscopy (TEM) is a powerful tool for unveiling the structural, compositional, and electronic properties of organic-inorganic hybrid perovskites (OIHPs) at the atomic to micrometer length scales. However, the structural and compositional instability of OIHPs under electron beam radiation results in misunderstandings of the microscopic structure-property-performance relationship in OIHP devices. Here, ultralow dose TEM is utilized to identify the mechanism of the electron-beam-induced changes in OHIPs and clarify the cumulative electron dose thresholds (critical dose) of different commercially interesting state-of-the-art OIHPs, including methylammonium lead iodide (MAPbI(3)), formamidinium lead iodide (FAPbI(3)), FA(0.83)Cs(0.17)PbI(3), FA(0.15)Cs(0.85)PbI(3), and MAPb(0.5)Sn(0.5)I(3). The critical dose is related to the composition of the OIHPs, with FA(0.15)Cs(0.85)PbI(3) having the highest critical dose of approximate to 84 e angstrom(-2) and FA(0.83)Cs(0.17)PbI(3) having the lowest critical dose of approximate to 4.2 e angstrom(-2). The electron beam irradiation results in the formation of a superstructure with ordered I and FA vacancies along (c), as identified from the three major crystal axes in cubic FAPbI(3), (c), (c), and (c). The intragrain planar defects in FAPbI(3) are stable, while an obvious modification is observed in FA(0.83)Cs(0.17)PbI(3) under continuous electron beam exposure. This information can serve as a guide for ensuring a reliable understanding of the microstructure of OIHP optoelectronic devices by TEM.

Deciphering the atomic and electronic structures of interfaces is key to developing state-of-the-art perovskite semiconductors. However, conventional characterization techniques have limited previous studies mainly to grain-boundary interfaces, whereas the intragrain-interface microstructures and their electronic properties have been much less revealed. Herein using scanning transmission electron microscopy, we resolved the atomic-scale structural information on three prototypical intragrain interfaces, unraveling intriguing features clearly different from those from previous observations based on standalone films or nanomaterial samples. These intragrain interfaces include composition boundaries formed by heterogeneous ion distribution, stacking faults resulted from wrongly stacked crystal planes, and symmetrical twinning boundaries. The atomic-scale imaging of these intragrain interfaces enables us to build unequivocal models for the ab initio calculation of electronic properties. Our results suggest that these structure interfaces are generally electronically benign, whereas their dynamic interaction with point defects can still evoke detrimental effects. This work paves the way toward a more complete fundamental understanding of the microscopic structure–property–performance relationship in metal halide perovskites.

The first challenge in the commercialization of perovskite solar cells (PSCs) is how to easily fabricate large-scale, high-quality perovskite films. Although some methods have been developed for the fabrication of large-scale films, the film quality still needs to be improved. The MA0 healing method, as a post-processing technique, can be perfectly combined with other large-scale methods. However, determining the mechanism of the whole process is crucial for commercial production and subsequent research. Herein, we summarize the research progress on the MA0 healing method. Firstly, we introduce the interaction during the liquification process including the interaction of amines with Pb2+, the generation of hydrogen bonds, the influence of H2O, and the reactions between different amines. Then, we systematically discuss the dynamic mechanism of adsorption and desorption. Finally, several aspects that need to be further clarified are proposed.

Featuring sulfonyl, an organic small molecule, 3-ethylbenzo[d]isothiazole 1,1-dioxide (PSAD), is introduced to effectively passivate defects in perovskite films via hydrogen bonding and coordination bonding interactions, affording devices with higher efficiency and better operational stability.

Metal-cation defects and halogen-anion defects in perovskite films are critical to the efficiency and stability of perovskite solar cells (PSCs). In this work, a random polymer, poly(methyl methacrylate-co-acrylamide) (PMMA-AM), was synthesized to serve as an interfacial passivation layer for synergistically passivating the under-coordinated Pb

Molecular doping is an of significance approach to reduce defects density of perovskite and to improve interfacial charge extraction in perovskite solar cells. Here, we show a new strategy for chemical doping of perovskite via an organic small molecule, which features a fused tricyclic core, showing strong intermolecular π-Pb 2+ interactions with under-coordinated Pb 2+ in perovskite. This π-Pb 2+ interactions could reduce defects density of the perovskite and suppress the nonradiative recombination, which was also confirmed by the density functional theory calculations. In addition, this doping via π-Pb 2+ interactions could deepen the surface potential and downshift the work function of the doped perovskite film, facilitating the hole extraction to hole transport layer. As a result, the doped device showed excellent efficiency of 21.41% with ignorable hysteresis. This strategy of fused tricyclic core-based doping provides a new perspective for the design of new organic materials to improve the device performance.

MAPbI3, one of the archetypical metal halide perovskites, is an exciting semiconductor for a variety of optoelectronic applications. The photoexcited charge-carrier diffusion and recombination are important metrics in optoelectronic devices. Defects in grain interiors and boundaries of MAPbI3 films cause significant nonradiative recombination energy losses. Besides defect impact, carrier diffusion and recombination anisotropy introduced by structural and electronic discrepancies related to the crystal orientation are vital topics. Here, large-sized MAPbI3 single crystals (SCs) were grown, with the (110), (112), (100), and (001) crystal planes simultaneously exposed through the adjusting ratios of PbI2 to methylammonium iodide (MAI). Such MAPbI3 SCs exhibit a weak n-type semiconductor character, and the Fermi levels of these planes were slightly different, causing a homophylic p-n junction at crystal ledges. Utilizing MAPbI3 SCs, the photoexcited carrier diffusion and recombination within the crystal planes and around the crystal ledges were investigated through time-resolved fluorescence microscope. It is revealed that both the (110) and (001) planes were facilitated to be exposed with more MAI in the growth solutions, and the photoluminescence (PL) of these planes manifesting a red-shift, longer carrier lifetime, and diffusion length compared with the (100) and (112) planes. A longer carrier diffusion length promoted photorecycling. However, excessive MAI-assisted grown MAPbI3 SCs could increase the radiative recombination. In addition, it revealed that the carrier excited within the (001) and (112) planes was inclined to diffuse toward each other and was favorable to be extracted out of the grain boundaries or crystal ledges.

Dion-Jacobson phase two-dimensional (DJ 2D) perovskites, recently attracting considerable interests, exhibit excellent environmental stability and structural tunability, but their solar cells still offer unsatisfactory power conversion efficiencies (PCEs). Herein, we develop DJ 2D perovskites employing formamidinium (FA+) as a ternary cation in the perovskite cages ((PDA)(FA)x(MA)3−xPb4I13, x = 0, 0.15, 0.3 and 0.6, PDA = 1,3-propanediammonium) for highly efficient and stable perovskite solar cells (PSCs). We found that the DJ 2D perovskite with a 10% FA+ fraction presents improved crystallinity, preferred vertical orientation, and longer charge carrier lifetime compared to that without FA+ doping. As a result, the FA-doped DJ 2D PSCs exhibit a champion PCE of 14.74% with superior device stability. The unencapsulated devices sustain over 92% of its initial PCE after storage at a constant relative humidity (RH) of 65% for 6000 h, 90% by heat at 85 °C in air for 800 h, and 94% under 1-sun illumination for 5000 h. These findings demonstrate that the incorporation of FA cation into the DJ 2D perovskite is a promising strategy to develop highly efficient and stable DJ 2D PSCs.

We report a simple and effective method to realize desirable interfacial property for inverted planar perovskite solar cells (PSCs) by using small molecule ethanediamine for the construction of a novel polyelectrolyte hole transport material (P3CT-ED HTM). It is found that P3CT-ED can not only improve the hole transport property of P3CT-K but also improve the crystallinity of adjacent perovskite film. In addition, the introduction of ethanediamine into P3CT realigns the conduction and valence bands upwards, passivates surface defects and reduces nonradiative recombination. As a consequence, compared to P3CT-K hole transport layer (HTL) based devices, the average power conversion efficiency (PCE) is boosted from 17.2% to 19.6% for the counterparts with P3CT-ED, with simultaneous enhancement in open circuit voltage and fill factor. The resultant device displays a champion PCE of 20.5% with negligible hysteresis.

High-performance planar perovskite solar cells (PSCs) are dependent on the properties of electron transport layers (ETLs). Here, we report an effective interface engineering strategy by incorporating an oxidized form of graphdiyne into a SnO2 ETL. In addition to the unique structural properties of graphdiyne, graphdiyne oxide (GDYO) is characteristic of additional hydrophilic carboxy and hydroxy functional groups that may form chemical bonds with uncoordinated Sn. The interaction thereof is able to reduce the oxygen vacancy within SnO2, thereby passivating the surface defects of SnO2; this promotes electron transport while also suppressing non-radiative recombination. Notably, the work function of the GDYO-doped SnO2 film matches well with the perovskite conduction band, resulting in a high open circuit voltage. As a consequence, the GDYO-containing device demonstrated a high PCE of 21.23% with a VOC of 1.13 V, a JSC of 24.49 mA cm−2 and an FF of 76.85%, superior to those of the control device without GDYO. Furthermore, the unencapsulated device maintained 84% of the initial efficiency after 80 °C for 24 days and 71% after continuous illumination for 160 h. This work provides guidance for developing efficient and stable perovskite devices from the perspective of optimizing interface properties, presenting great potential of functionalized graphdiyne for practical applications.

Summary The studies of perovskite film in the perovskite solar cells (PSCs) mainly focus on their crystallization and growth, but the reactions that happen in the precursor solutions are still not very clear, which is leading to the bad reproducibility for high-efficient devices. We demonstrated that, in the methylammonium- and formamidinium-mixed organic cation perovskite solution, the methylamine molecule could be first generated from the deprotonation of methylammonium iodide, and then condensate with formamidinium iodide to form N-methyl formamidinium iodide and N, N′-dimethyl formamidinium iodide. The triethyl borate was carried out as a stabilizer to restrain the deprotonation of methylammonium iodide in the precursor solutions, resulting in the elimination of the impurity phase in perovskite films. We think that the introduction of stabilizer in the perovskite precursor solution will become a common strategy for mixed-organic-cation PSCs in the future to improve the reproducibility and efficiency.

Poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (PTAA) represents the state-of-the-art hole transport material (HTM) in inverted perovskite solar cells (PSCs), however, unsatisfied surface properties of PTAA as well as high energy disorder in the bulk film hinder the further enhancement of device performance. Herein, we strategically develop a simple small molecule 10-(4-(3,6-dimethoxy-9H-carbazol-9-yl)phenyl)-3,7-bis(4-vinylphenyl)-10H-phenoxazine (MCz-VPOZ) for in-situ crosslinking of polymer hole conductor (CL-MCz) via a facile and low-temperature cross-linking technology. The resulting polymer CL-MCz offers high energy ordering, improved electrical conductivity as well as appropriate energy-level alignment, enabling efficient charge carrier collection in the devices. Meanwhile, CL-MCz synchronously provides satisfied surface wettability and interfacial functionalization, facilitating the formation of high-quality perovskite films with fewer bulk iodine vacancies and suppressed carrier recombination. Significantly, the device with CL-MCz yields a champion power conversion efficiency of 23.9% along with an extremely low energy loss down to 0.41 eV, which represents the highest reported efficiency for non-PTAA based polymer HTMs in inverted PSCs. Furthermore, the corresponding unencapsulated devices exhibited competitive shelf-life stability under various operational stressors up to 2500 hours, reflecting high promises of CL-MCz in the scalable PSC application. This work underscores the promising potential of the cross-linking approach in preparing low-cost, stable and efficient polymer HTMs toward reliable PSCs. This article is protected by copyright. All rights reserved.

In solution-processed organic-inorganic halide perovskite films, halide-anion related defects including halide vacancies and interstitial defects can easily form at the surfaces and grain boundaries. The uncoordinated lead cations produce defect levels within the band gap, and the excess iodides disturb the interfacial carrier transport. Thus these defects lead to severe nonradiative recombination, hysteresis, and large energy loss in the device. Herein, polyacrylonitrile (PAN) was introduced to passivate the uncoordinated lead cations in the perovskite films. The coordinating ability of cyano group was found to be stronger than that of the normally used carbonyl groups, and the strong coordination could reduce the I/Pb ratio at the film surface. With the PAN perovskite film, the device efficiency improved from 21.58 % to 23.71 % and the open-circuit voltage from 1.12 V to 1.23 V, the ion migration activation energy increased, and operational stability improved.

Low production cost and ever-increasing efficiencies make perovskite solar cells a flourishing area of research. The high efficiency originates from not only the unique optoelectronic properties of perovskites, but also various device optimization strategies, such as interfacial engineering, defect engineering, and componential engineering. Behind these strategies stand the fundamental intermolecular interactions and bondings, such as hydrogen bonding, halide bonding, ionic bonding, Lewis acid–base interactions, and van der Waals interactions. In this review, we focus on different types of interactions and summarize the progresses made in perovskite solar cells. Additionally, perspectives on further efforts in improving device performance and stability are presented.

Developing dopant-free hole transporting materials (HTMs) and passivating defects in perovskite films are two significant themes to realize efficient and stable perovskite solar cells (PSCs). Compared to various individual endeavors for either of them, enabling both via a single material is more interesting but certainly challenging. In this report, we develop dopant-free polymer HTMs bearing amino pendants as passivating groups for improved efficiency and stability of PSCs. The bifunctional polymers present simultaneous main-chain (donor–acceptor conjugated backbone) hole extraction/transport and side-chain (amino group) defect passivation at the perovskite/HTM interface. Moreover, with an increased content of amino pendants, the polymers exhibit enhanced hole mobility and defect passivation ability, advancing device efficiency and stability. As a result, PSCs using the dopant-free polymer HTM achieve an efficiency approaching 19%, with impressive stability when testing at a relative humidity of 85%, by heat at 80 °C, or under continuous light illumination. This work demonstrates that amino functionalization at the side chain of polymers is a promising method to develop dopant-free HTMs accompanied by defect passivation effects for high-performance and durable PSCs.

In the past ten years, perovskite solar cells (PSCs) have achieved tremendous success, with the efficiency rivalling that of conventional silicon-based devices. To promote commercialization, lowering the production cost and reducing the complexity of the process would make the devices more competitive and thus are highly required. In this respect, inverted hole-transport-layer-free (HTL-free) PSCs were developed and have been attracting extensive attention. To date, the efficiency of inverted HTL-free PSCs has surpassed 20%, and 90% of the initial efficiency can be retained after 1000 h of continuous illumination, showing their great application potential. In this mini-review, we summarize the development and progress of inverted HTL-free PSCs. The universality of inverted HTL-free structures (including flexible and semi-transparent devices) and stability are also discussed. Finally, promising research directions are suggested to further advance the inverted HTL-free PSCs.

Photopowered energy systems (PPESs), which simultaneously achieve power conversion and energy storage, are one of the most promising auxiliaries to fulfill the giant and diversified power demand in modern society. Devices with a low cost, wearable, compact structure and the potential to add a variety of features (such as photochromic, flexible, textile, and wearable) have received extensive research attention. Photo-supercapacitors are becoming one of the most extensively researched PPESs due to their ease of fabrication, mitigation of solar irradiation discontinuities, and the promotion of renewable energy utilization, and these devices have been fabricated with different combinations of photovoltage devices and energy-storage technologies. This review summarizes the development of photo-supercapacitors that integrate third-generation solar cells and supercapacitors, with a focus on materials alignment, performance, structure design, and application. Finally, current challenges, possible solutions, and future perspectives are discussed.

MAPbI

Molecular doping is an of significance approach to reduce defects density of perovskite and to improve interfacial charge extraction in perovskite solar cells. Here, we show a new strategy for chemical doping of perovskite via an organic small molecule, which features a fused tricyclic core, showing strong intermolecular π-Pb

Slot-die coating holds advantages over other large-scale technologies thanks to its potential for well-controlled, high-throughput, continuous roll-to-roll fabrication. Unfortunately, it is challenging to control thin.film uniformity over a large area while maintaining crystallization quality. Herein, by using a high-pressure nitrogen-extraction (HPNE) strategy to assist crystallization, a wide processing window in the well-controlled printing process for preparing high-quality perovskites is achieved. The yellow-phase perovskite generated by the HPNE acts as a crucial intermediate phase to produce large-area high-quality perovskite film. Furthermore, an ionic liquid is developed to passivate the perovskite surface to reduce surface defect density and to suppress carrier recombination, resulting in significantly increased efficiency to 22.7%, the highest for large-area fabrication. The strategies are successfully extended to large-area device fabrication, making it possible to produce a 40 × 40 mm2 module with stabilized PCE as high as 19.4%, the highest-efficiency for a large-area module to date.

Various methods have been developed to optimize the active layer of perovskite solar cells. To date, the introduction of excess PbI2 and chlorine doping are two typical means. Herein, an ion exchange–decomposition process was designed to combine these two approaches. In this process, the I–Cl exchange and MACl sublimation occurred simultaneously at elevated temperature, resulting in a PbI2-excess, Cl-doped perovskite film. This combined strategy could guarantee that as much chlorine as possible was doped into the perovskite crystal lattice, which enables the production of perovskite films with obviously reduced defect density and enhanced carrier diffusion length. Strikingly, the power conversion efficiency of the device is boosted from 17.17% to 20.15%.

Summary Here, we sucessfully demonstrate the continuous functionalization of grain boundaries (GBs) in CH 3 NH 3 PbI 3 (MAPbI 3 ) organic-inorganic halide perovskite (OIHP) thin films with a triblock copolymer that contains rationally selected hydrophilic-hydrophobic-hydrophilic symmetric blocks. The addition of the triblock copolymer into the precursor solution assists in perovskite solution crystallization, resulting in ultrasmooth thin films with GB regions that are continuously functionalized. Tuning of the thickness of the functionalized GBs is realized, leading to MAPbI 3 OIHP thin films with simultaneously enhanced optoelectronic properties and environmental (thermal, moisture, and light) stability. The resulting perovskite solar cells show high stabilized efficiency of 19.4%, most of which is retained (92%) upon 480-hr 1-sun illumination. This approach is generic in nature, and it can be extended to a wide range of OIHPs and beyond.

Graphene-wrapped iron carbide nanoparticles (Fe3C@G) are employed as an alternative counter electrode to Pt in dye-sensitized solar cell via a convenient magnetic field induced assembly method. Benefit from the novel binder-free electrode fabrication route, the Fe3C@G nanosheets orderly are deposited on the FTO glass to form an effective catalyst layer with both favorable catalytic ability and electron migration rate. Comparable photovoltaic conversion efficiency with Pt endows the Fe3C@G a promising counter electrode for low cost but high performance dye-sensitized solar cells. Moreover, the magnetic field induced assembly method also shows potential application for other magnetic materials towards counter electrode.

Interface engineering is a crucial strategy to improve the performance of the perovskite solar cells. The introduction of excess PbI2 with simple mixing method is widely used, but unfortunately its underlying mechanism is still unclear. The main reason is the lack of direct evidence with precise control of the PbI2 distribution. Herein, a program-controlled pulsed H2O vapor exposure/purge method was developed to evenly generate thin PbI2 layer on the film surface. Based on this method, it was found that different PbI2 locations play a different effects on the photovoltaic performance of the perovskite solar cells. In the normal device structure, the performance improvement is owing to the passivation effect, while in the inverted device structure, the energy level alignment plays a more dominant role. The discoveries based on the PbI2 location controllable method are conducive to our new understanding of the traditional PbI2-rich system and thus can be a direction towards highly efficient perovskite solar cells.

Solution-processed organic–inorganic halide perovskite (OIHP) thin films typically contain fine, randomly oriented grains and a high-density grain-boundary network, which are unfavorable for key film functions including charge transport and environmental stability. Here, we report a new chemical route for achieving CH3NH3PbI3 (MAPbI3) OIHP thin films comprising large, uniaxially oriented grains and an ultralow-density grain-boundary network. This route starts with a new metastable liquid-state precursor phase, MAPbI3·MACl·xCH3NH2, which converts to metastable MAPbI3·MACl and then to MAPbI3 OIHP upon stepwise release of volatile CH3NH2 and MACl. Perovskite solar cells made via this route show high power conversion efficiency of up to 19.4%, with significantly enhanced environmental stability.

The stability issue is still one of the main limitations of the commercialization of perovskite photovoltaics. The mixed cation FA

The stability of the perovskite/electron transport layer (ETL) interface is critical for perovskite solar cells due to the presence of ultraviolet (UV) light in the solar spectrum. Herein, we have studied the decomposition process and performance evolution of the perovskite layer in contact with different ETLs under strong ultraviolet irradiation. The normally used SnO2 layer has lower photocatalytic activity in comparison with the TiO2 layer, but the perovskite/SnO2 interface is still severely decomposed along with the formation of hole structures. Such UV light-induced decomposition, on the one hand, leads to the decomposition of the perovskite phase into PbI2 and more seriously, the formed hole structure significantly limits the carrier injection at the interface owing to the separation of the perovskite active layer from ETLs. Under the same conditions, the perovskite/PCBM interface is very stable and maintains a highly efficient carrier injection. There is no significant efficiency degradation of the encapsulated PCBM-based devices measured outdoors for about three months.

The addition of a polar-hydrophobic methylammonium trifluoroacetate ionic liquid tailors the hydrophobicity of halide-perovskite precursor solutions and assists in grain growth. This unique additive also functionalizes the grain boundaries via polar-polar interactions, thereby enhancing the optoelectronic properties and chemical stability of perovskites. This study opens the door to the solution hydrophobicity control towards high-performance perovskite devices.