JIALINGBO

Novel asymmetric alkoxy and alkyl substitutions on the well‐known nonfullerene acceptor Y6 yield a molecule named Y6‐1O, and its photoelectric properties and photovoltaic performance are systematically compared with the two related symmetric molecules (Y6 and Y6‐2O), which suggests that this design strategy is promising and effective.

Abstract

In this paper, a strategy of asymmetric alkyl and alkoxy substitution is applied to state‐of‐the‐art Y‐series nonfullerene acceptors (NFAs), and it achieves great performance in organic solar cell (OSC) devices. Since alkoxy groups can have a significant influence on the material properties of NFAs, alkoxy substitution is applied to the Y6 molecule in a symmetric manner. The resulting molecule (named Y6‐2O), despite showing improved open‐circuit voltage (V _oc), yields extremely poor performance due to low solubility and excessive aggregation properties, a change that is due to the conformational locking effect of alkoxy groups. In contrast, asymmetric alkyl and alkoxy substitution on Y6, yields a molecule named Y6‐1O that can maintain the positive effect of V _oc improvement and obtain reasonably good solubility. The resulting molecule Y6‐1O enables highly efficient nonfullerene OSCs with 17.6% efficiency and the asymmetric side‐chain strategy has the potential to be applied to other NFA‐material systems to further improve their performance.

Herein, the chemistry of tin perovskite compounds for the fabrication of high‐efficiency nontoxic solar cells is described. The reaction mechanisms among the compounds and additives present in the Sn perovskite films are discussed to correlate with the device performance.

Lead (Pb)‐based perovskite solar cells (Pb‐PSCs) have been recorded with a fascinating power conversion efficiency (PCE) of 25.5%. However, the presence of toxic Pb in the perovskite absorber material hinders the commercial aspects of Pb‐PSCs as a promising and efficient new generation of solar cells. Fortunately, theoretical calculations have predicted that tin (Sn)‐based perovskite solar cells (Sn‐PSCs) could have superior performance comparable to the Pb‐PSCs. Recently, many approaches have been reported for developing efficient Sn‐PSCs but yet they have shown the best PCE of 13.24%. This low PCE compared to Pb‐PSCs might be because Sn‐PSCs have been approached in the same way as Pb‐PSCs. However, from a chemistry viewpoint, the understanding of Sn‐PSCs might be very different from that of Pb‐based ones. Herein, the fundamental knowledge of the chemistry and coordination chemistry of Sn^II compounds and their structural properties is described. Then, an insight is provided into understanding the recent trends of Sn perovskite formation using various Lewis base additives in the precursor solution and incorporation as a cation in the perovskite lattice. Finally, the influence of utilizing Lewis base additives on the device dynamics is discussed.

Utilizing NP‐SC₆‐TiOPc and NP‐SC₆‐ZnPc as passivating agents on perovskite thin film through an antisolvent, improved performance and stability are achieved for perovskite solar cells. The highest power conversion efficiencies (PCEs) of 19.39% and 18.04% are obtained for NP‐SC₆‐TiOPc and NP‐SC₆‐ZnPc passivated devices, which is higher than that of the control devices without post‐treating the MAPbI₃ films (PCE of 17.67%).

Abstract

Semiconducting molecules have been employed to passivate traps extant in the perovskite film for enhancement of perovskite solar cells (PSCs) efficiency and stability. A molecular design strategy to passivate the defects both on the surface and interior of the CH₃NH₃PbI₃ perovskite layer, using two phthalocyanine (Pc) molecules (NP‐SC₆‐ZnPc and NP‐SC₆‐TiOPc) is demonstrated. The presence of lone electron pairs on S, N, and O atoms of the Pc molecular structures provides the opportunity for Lewis acid–base interactions with under‐coordinated Pb²⁺ sites, leading to efficient defect passivation of the perovskite layer. The tendency of both NP‐SC₆‐ZnPc and NP‐SC₆‐TiOPc to relax on the PbI₂ terminated surface of the perovskite layer is also studied using density functional theory (DFT) calculations. The morphology of the perovskite layer is improved due to employing the Pc passivation strategy, resulting in high‐quality thin films with a dense and compact structure and lower surface roughness. Using NP‐SC₆‐ZnPc and NP‐SC₆‐TiOPc as passivating agents, it is observed considerably enhanced power conversion efficiencies (PCEs), from 17.67% for the PSCs based on the pristine perovskite film to 19.39% for NP‐SC₆‐TiOPc passivated devices. Moreover, PSCs fabricated based on the Pc passivation method present a remarkable stability under conditions of high moisture and temperature levels.

Due to the poor morphology and crystallinity of Sn–Pb mixed perovskites, it is found that the addition of potassium thiocyanate (KSCN) can effectively reduce the bulk defects and carrier recombination through optimizing the process of film formation and the perovskite film quality. Therefore, a whole improvement of device performance can be achieved under the optimization effect of KSCN doping.

The organic–inorganic Sn–Pb mixed perovskite has achieved great progress during the last 10 years and is considered as one of the most promising low‐bandgap photovoltaic materials. It has lower toxicity, outstanding optoelectrical properties, and achieved remarkable performance. However, there are still plenty of challenges in controlling the morphology, crystallinity, and defects of the Sn–Pb mixed perovskite film because of the inferior chemical stability of Sn compared with Pb. Herein, it is found that the synergistic effect of potassium thiocyanate (KSCN) in the Sn–Pb mixed perovskites can enlarge the grain size, enhance the crystallization, improve the film morphology, and obtain high‐quality perovskite films which effectively eliminate the bulk defects and smooth carrier transportation of Sn–Pb mixed perovskite solar cells. Through optimizing the concentration of KSCN, a high‐performance MA_0.5FA_0.5Pb_0.5Sn_0.5I₃ solar cell with an efficiency of 15.14% and improved stability is obtained. This work lays a key foundation for the fabrication of efficient and stable Sn‐based or Sn–Pb mixed perovskite solar devices.

Bearing high hole mobility and appropriate energy levels, an organic small molecule 2,7‐bis(4‐octylphenyl)naphtho[2,1‐b:6,5‐b 0] difuran (C₈‐DPNDF) is introduced as a dopant‐free hole transporting material in inverted perovskite solar cells. The device with C₈‐DPNDF as HTM shows a decent power conversion efficiency of 17.5% and can keep 92% of its initial value after 30 days in ambient air.

Hole transport material (HTM) is a significant constituent in perovskite solar cells (PSCs). However, HTM generally is not utilized in its pristine form but with dopants (such as lithium salt, tert‐butyl pyridine, F₄‐TCNQ), which accelerates device degradation and leads to poor stability. Therefore, dopant‐free HTM is highly desirable to fabricate stable devices. Herein, a fused furan organic small molecule (C₈‐DPNDF) is introduced as a dopant‐free HTM in inverted PSCs. As a potential HTM candidate, C₈‐DPNDF shows excellent properties, such as high hole mobility, matched energy level with perovskite, and resistance to perovskite precursor solution. As a result, the device based on C₈‐DPNDF as HTM shows a power conversion efficiency (PCE) of 17.5%, compared with 17.1% of the control device based on classic poly(bis(4‐phenyl)(2,4,6‐trimethylphenyl)amine) (PTAA) as the HTM. In addition, the unencapsulated device based on C₈‐DPNDF as HTM keeps 92% of its initial PCE after 30 days of storage in ambient air with a relative humidity of ≈40%. This finding is expected to pave the way toward stable and highly efficient inverted PSCs based on dopant‐free HTMs.

Inorganic CsPbI3 perovskite is the most competitive candidate to hybrid perovskites. However, its poor phase stability, hydrophobicity and high‐density defects have limited the development of CsPbI3 perovskite solar cells (PSCs). To overcome these obstacles for achieving high‐performance CsPbI3 PSCs, additive engineering has been widely employed. Herein, the progress of additive engineering in CsPbI3 PSCs is systematically reviewed.

All‐inorganic perovskite solar cells (PSCs) have attracted a lot of attention in the past few years because of their preeminent thermal stability compared with organic–inorganic hybrid PSCs. Among all kinds of all‐inorganic perovskites, CsPbI₃ perovskite with a proper bandgap of ≈1.7 eV becomes the most competitive candidate. However, its poor phase stability, hydrophobicity, and high‐density defects have limited the development of CsPbI₃ PSCs. To overcome these obstacles for achieving high‐performance CsPbI₃ PSCs, additive engineering has been widely used, which has rapidly promoted the power conversion efficiency (PCE) to over 19%. Herein, the progress of additive engineering in CsPbI₃ PSCs is systematically reviewed. First, the roles of additives in CsPbI₃ PSCs are introduced, including improving phase stability, increasing moisture resistance, and passivating defects. Then, the additive engineering is categorized (additive engineering in perovskites and at perovskite/hole transport layer interfaces) and reviewed in detail. Finally, future research directions on additive engineering are suggested for further enhancing stability and improving PCE.

Herein, the origin of figures of merit for open‐circuit voltage, short‐circuit current density, and fill factor is discussed. Three design strategies of interface engineering, bandgap engineering, and process‐control engineering are proposed. The process‐control engineering is introduced, including fabrication atmosphere, synthesis routes, architecture optimization, physical deposition condition, and chemical process with multiple degrees of freedom.

Organic/inorganic lead‐halide perovskite and its solar cells (SCs) present a new research platform for the study of special photophysical and photovoltaic (PV) characteristics across materials science, chemistry, physics, and engineering disciplines. However, the current understanding of the crystal structures, origins of figures of merit, and design strategies of SCs is inadequate. These key parameters are critical for exploring further applications of organometallic‐halide perovskite films and their SCs. Therefore, herein, the material characteristics of lead‐halide perovskite are introduced, the origins of open‐circuit voltages, short‐circuit current densities, and fill factors are explored, and three design strategies using interface engineering, bandgap engineering, and process‐control engineering for high‐quality perovskite active‐layer fabrication, outstanding efficiency, and stable SCs are summarized. Herein, process‐control engineering is introduced for the first time in perovskite SCs. Based on favorable synergistic effects, these structural features, origins of crucial parameters, and design strategies all promote the development of new schemes to explore the underlying physics, optimize functional layers and cell architectures, and improve final PV performance and device stability.

The dimensionality, optoelectronic properties, and stability of lead halide perovskite films can be fine‐tuned via surface passivation with bulky fluoroaromatic cations. This study demonstrates the practical use of fluorinated phenethylammonium iodide (FPEAI) for simultaneous efficiency and stability improvement in large‐area perovskite solar cell devices and modules.

State‐of‐the‐art perovskite solar cells (PSCs) based on three‐dimensional (3D) films have achieved high power conversion efficiencies (PCEs), but are relatively fragile in high‐temperature and humid environments. This shortcoming must be addressed before PSCs can be fully commercialized. Herein, the use of a fluorinated aromatic organic spacer cation, 4‐fluoro‐phenethylammonium iodide (FPEAI), to fine‐tune the dimensionality and surface morphology of perovskite films is demonstrated. Surface treatment with FPEAI can lead to in situ formation of a two‐dimensional (2D) (FPEA)₂PbI₄ perovskite capping layer atop a 3D perovskite film, producing novel 3D/2D interface in perovskite films. Simultaneously, FPEAI treatment can induce a novel grain‐boundary passivation effect on the film surface, which helps to suppress undesirable charge recombination. After FPEAI treatment, standard (0.09 cm²) and large‐area (2.00 cm²) PSCs achieve PCEs of 20.53% and 16.82%, respectively. The FPEAI‐treated PSCs also demonstrate superior air‐ and photo‐stability due to the hydrophobic (FPEA)₂PbI₄ capping layer that reduces moisture ingress into perovskite structures. Furthermore, a 11.2 cm² large FPEAI‐treated PSC module with a PCE of 13.66% are successfully fabricated. FPEAI passivation is a facile strategy to produce 3D/2D multi‐dimensional PSCs with superior performance and stability.

Good thermal shock resistance and high absorptivity in a wide spectral range, as the two key aspects of photothermal coating in high‐temperature applications, are seldomly realized simultaneously. Here, it is reported that a reticular porous Ca‐doped LaCrO₃ perovskite photothermal coating fabricated by a simple process presents excellent thermal shock resistance between 1200 °C and room temperature and optical absorptivity of ∽94% in the wavelength range of 0.3—14 μm. The high‐temperature sintering after the screen printing can trigger significant variations in microchemistry and microstructure of the Ca‐doped LaCrO₃ coatings, and the experimental analyses and the first‐principles calculation demonstrate that the appropriate doping of Ca²⁺ can cause lattice distortion, decrease the lattice parameters and bandgap, and effectively enhance interactions between photon and carrier, resulting in the high optical absorptivity in the visible, near‐ and mid‐infrared ranges. The reticular porous microstructure and interfacial diffusion bonding between the coating and the Al₂O₃ substrate with a gradient transition layer can contribute to the high‐temperature thermal shock resistance. This study provides a novel way to fabricate a high‐performance and low‐cost photothermal conversion coating, which can present a broad application prospect in energy harvesters and sensors.

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The working on the interfacial engineering toward efficient and stable perovskite solar cells (PSCs) is demonstrated. The key role of 2D interface modification for efficient and stable perovskite solar cells is highlighted, especially for the energy band alignment of PSCs. This paper sheds light on the significance of 2D interface modification in PSCs and provides critical guidance for development of highly efficient and stability PSCs.

Abstract

Interfacial engineering is essential for facilitating carrier separation, charge extraction, and enhancing the stability in organic–inorganic perovskite solar cells (PSCs). Herein, a facile and effective method is demonstrated not only to tune the electronic performance of electron transporting layer (ETL) but also to passivate the defects at the interface between the ETL and perovskite. On the top of the tin(IV) oxide (SnO₂) ETL, butylammonium chloride (BACl) and lead(II) iodide (PbI₂) are introduced as interface to modify the ETL/perovskite interface. The PSCs with interface modified exhibit a power conversion efficiency (PCE) of 21.15%, compared to 18.33% for the device without interface modified. Such enhancement in efficiency is mainly attributed to a better energy band alignment, and the quality of perovskite films is improved through the interface modification, thus enhancing photogenerated charge extraction and leading to low charge carrier recombination at the interface of ETL/perovskite. Furthermore, the device with interface modified exhibits significant stability. This work provides an alternative strategy on the ETL/perovskite interface to obtain highly stable and efficient PSCs.

Passivation approaches of perovskite surface are key to improve the light stability of the perovskite solar cells. However, the passivation strategy is still required to enhance the durability of the perovskite layer. Here, a promising passivation concept is demonstrateed by applying a fluorinated agent on the perovskite layer for light stability improvement. Such fluorinated passivation agents could prevent the formation of Pb⁰ at the perovskite surface resulting in suppressing a defect induced recombination and improving the durability of the perovskite solar cells. As an additional benefit, the fluorinated passivation agent increases the V _OC which improves the photovoltaic performance of the perovskite solar cells. Consequently, with a fluorinated passivation agent, the perovskite maintains a power conversion efficiency of 95% after 300 h of light illumination. It was found that the fluorinated passivation material of 1H,1H,2H,2H‐perfluorooctyltriethoxysilane (PFOTES) can improve the stability of the perovskite solar cells.

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C−C oxidative dimerizations of α‐aryl ketonitriles are realized by using zwitterionic ligand capped CsPbBr₃ perovskite QDs as catalysts under visible light illumination, via a radical mediated reaction pathway. High stereoselectivities of dl‐isomers were obtained owing to less steric hindrance during the bond formation process. Our study sheds new lights on using lead‐halide perovskite QDs as photocatalysts for stereoselective organic synthesis.

Abstract

Semiconductor quantum dots (QDs) have attracted tremendous attention in the field of photocatalysis, owing to their superior optoelectronic properties for photocatalytic reactions, including high absorption coefficients and long photogenerated carrier lifetimes. Herein, by choosing 2‐(3,4‐dimethoxyphenyl)‐3‐oxobutanenitrile as a model substrate, we demonstrate that the stereoselective (>99 %) C−C oxidative coupling reaction can be realized with a high product yield (99 %) using zwitterionic ligand capped CsPbBr₃ perovskite QDs under visible light illumination. The reaction can be generalized to different starting materials with various substituents on the phenyl ring and varied functional moieties, producing stereoselective dl‐isomers. A radical mediated reaction pathway has been proposed. Our study provides a new way of stereoselective C−C oxidative coupling via a photocatalytic means using specially designed perovskite QDs.

Fluorinated‐based passivation agent suppresses Pb⁰ at the perovskite surface during a light soaking, which prevents from increasing the recombination pathway and results in improving the light stability of the perovskite solar cells. Consequently, a functional passivation strategy for enhancing light stability with the fluorinated passivation agent is demonstrated, maintaining a 95% photoconversion efficiency for 300 h under the light illumination.

Passivation approaches of perovskite surface are key to improve the light stability of perovskite solar cells. However, a passivation strategy is still required to enhance the durability of the perovskite layer. Here, a promising passivation concept is demonstrated by applying a fluorinated agent on the perovskite layer for light stability improvement. Such fluorinated passivation agents can prevent the formation of Pb⁰ at the perovskite surface resulting in suppressing a defect‐induced recombination and improving the durability of the perovskite solar cells. As an additional benefit, the fluorinated passivation agent increases the V _OC which improves the photovoltaic performance of the perovskite solar cells. Consequently, with a fluorinated passivation agent, the perovskite maintains a power conversion efficiency of 95% after 300 h of light illumination. It is found that the fluorinated passivation material of 1H,1H,2H,2H‐perfluorooctyltriethoxysilane (PFOTES) can improve the stability of the perovskite solar cells.

A straightforward polyTPD passivation is introduced to reduce the defect‐mediated recombination by elucidating the imperfections on the surface and grain boundaries of perovskite materials. Suppressed non‐radiative recombination and improved interfacial hole extraction result in perovskite solar cells with stabilized efficiency exceeding 21%. Moreover, ultra‐hydrophobic and thermally robust polyTPD passivated devices retain 94% of the initial efficiency after 800 h under operational conditions.

Abstract

The failure of perovskite solar cells (PSCs) to maintain their maximum efficiency over a prolonged time is due to the deterioration of the light harvesting material under environmental factors such as humidity, heat, and light. Systematically elucidating and eliminating such degradation pathways are critical to imminent commercial use of this technology. Here, a straightforward approach is introduced to reduce the level of defect‐states present at the perovskite and hole transporting layer interface by treating the various perovskite surfaces with poly(N,N′‐bis‐4‐butylphenyl‐N,N′‐bisphenyl)benzidine (polyTPD) molecules. This strategy significantly suppresses the defect‐mediated non‐radiative recombination in the ensuing devices and prevents the penetration of degrading agents into the inner layers by passivating the perovskite surface and grain boundaries. Suppressed non‐radiative recombination and improved interfacial hole extraction result in PSCs with stabilized efficiency exceeding 21% with negligible hysteresis (≈19.1% for control device). Moreover, ultra‐hydrophobic polyTPD passivant considerably alleviates moisture penetration, showing ≈91% retention of initial efficiencies after 300 h storage at high relative humidity of 80%. Similarly, passivated device retains 94% of its initial efficiency after 800 h under operational conditions (maximum power point tracking under continuous illumination at 60 °C). In addition to interfacial passivation function, hole‐selective role of dopant‐free polyTPD is also evaluated and discussed in this study.

An extraordinarily long stability, exceeding 1.5 years, for crosslinked perovskite nanoparticles (NPs) under harsh environments, by a novel materials design strategy, is reported. Surprisingly, the photoluminescence of the perovskite NPs is significantly increased under air, moisture, and chemicals, overcoming their instability in oxygen, water, and polar chemicals.

Abstract

Organic–inorganic hybrid perovskite nanoparticles (NPs) are a very strong candidate emitter that can meet the high luminescence efficiency and high color standard of Rec.2020. However, the instability of perovskite NPs is the most critical unsolved problem that limits their practical application. Here, an extremely stable crosslinked perovskite NP (CPN) is reported that maintains high photoluminescence quantum yield for 1.5 years (>600 d) in air and in harsher liquid environments (e.g., in water, acid, or base solutions, and in various polar solvents), and for more than 100 d under 85 °C and 85% relative humidity without additional encapsulation. Unsaturated hydrocarbons in both the acid and base ligands of NPs are chemically crosslinked with a methacrylate‐functionalized matrix, which prevents decomposition of the perovskite crystals. Counterintuitively, water vapor permeating through the crosslinked matrix chemically passivates surface defects in the NPs and reduces nonradiative recombination. Green‐emitting and white‐emitting flexible large‐area displays are demonstrated, which are stable for >400 d in air and in water. The high stability of the CPN in water enables biocompatible cell proliferation which is usually impossible when toxic Pb elements are present. The stable materials design strategies provide a breakthrough toward commercialization of perovskite NPs in displays and bio‐related applications.

Utilizing NP‐SC₆‐TiOPc and NP‐SC₆‐ZnPc as passivating agents on perovskite thin film through an antisolvent, improved performance and stability are achieved for perovskite solar cells. The highest power conversion efficiencies (PCEs) of 19.39% and 18.04% are obtained for NP‐SC₆‐TiOPc and NP‐SC₆‐ZnPc passivated devices, which is higher than that of the control devices without post‐treating the MAPbI₃ films (PCE of 17.67%).

Abstract

Semiconducting molecules have been employed to passivate traps extant in the perovskite film for enhancement of perovskite solar cells (PSCs) efficiency and stability. A molecular design strategy to passivate the defects both on the surface and interior of the CH₃NH₃PbI₃ perovskite layer, using two phthalocyanine (Pc) molecules (NP‐SC₆‐ZnPc and NP‐SC₆‐TiOPc) is demonstrated. The presence of lone electron pairs on S, N, and O atoms of the Pc molecular structures provides the opportunity for Lewis acid–base interactions with under‐coordinated Pb²⁺ sites, leading to efficient defect passivation of the perovskite layer. The tendency of both NP‐SC₆‐ZnPc and NP‐SC₆‐TiOPc to relax on the PbI₂ terminated surface of the perovskite layer is also studied using density functional theory (DFT) calculations. The morphology of the perovskite layer is improved due to employing the Pc passivation strategy, resulting in high‐quality thin films with a dense and compact structure and lower surface roughness. Using NP‐SC₆‐ZnPc and NP‐SC₆‐TiOPc as passivating agents, it is observed considerably enhanced power conversion efficiencies (PCEs), from 17.67% for the PSCs based on the pristine perovskite film to 19.39% for NP‐SC₆‐TiOPc passivated devices. Moreover, PSCs fabricated based on the Pc passivation method present a remarkable stability under conditions of high moisture and temperature levels.

The role of methylammonium chloride (MACl) in sequentially deposited bromine (Br)‐free formamidinium lead iodide (FAPbI₃)‐based perovskite is systematically demonstrated to regulate the PbI₂/FAI reaction, tune the phase transition at room temperature, and adjust the PbI₂ residual through an intermediate‐related perovskite decomposition during thermal annealing. The resulting optimized solar cells achieve a remarkable efficiency of 23.1% with considerably improved photostability.

Abstract

So far, the combination of methylammonium bromide/methylammonium chloride (MABr/MACl) or methylammonium iodide (MAI)/MACl is the most frequently used additives to stabilize formamidinium lead iodide (FAPbI₃) fabricated by the sequential deposition method. However, the enlarged bandgap due to the addition of bromide and the ambiguous functions of these additives in lead iodide (PbI₂) transformation are still worth considering. Herein, the roles of MACl in sequentially deposited Br‐free FA‐based perovskites are systematically investigated. It is found that MACl can finely regulate the PbI₂/FAI reaction, tune the phase transition at room temperature, and adjust intermediate‐related perovskite crystallization and decomposition during thermal annealing. Compared to FAPbI₃, the perovskite with MACl exhibits larger grain, longer carrier lifetime, and reduced trap density. The resultant solar cell therefore achieves a champion power conversion efficiency (PCE) of 23.1% under reverse scan with a stabilized power output of 23.0%. In addition, it shows much improved photostability under 100 mW cm⁻² white illumination (xenon lamp) in nitrogen atmosphere without encapsulation.

This work proposes an efficient method to produce tri‐iodide ions, which has been known as an efficient additive that improves the crystallinity, grain size, and morphology of perovskite films in a precursor solution using a photoassited process within short time, resulting in achieving the device performance up to 22%.

Abstract

One of the most effective methods to achieve high‐performance perovskite solar cells (PSCs) is to employ additives as crystallization agents or to passivate defects. Tri‐iodide ion has been known as an efficient additive to improve the crystallinity, grain size, and morphology of perovskite films. However, the generation and control of this tri‐iodide ion are challenging. Herein, an efficient method to produce tri‐iodide ion in a precursor solution using a photoassisted process for application in PSCs is developed. Results suggest that the tri‐iodide ion can be synthesized rapidly when formamidinium iodide (FAI) dissolved isopropyl alcohol (IPA) solution is exposed to LED light. Specifically, the photoassisted FAI–IPA solution facilitates the formation of fine perovskite films with high crystallinity, large grain size, and low trap density, thereby improving the device performance up to 22%. This study demonstrates that the photoassisted process in FAI dissolved IPA solution can be an alternative strategy to fabricate highly efficient PSCs with significantly reduced processing times.

Current density–voltage (J–V) hysteresis in perovskite solar cells (PSCs) is a major challenge in this field. Herein, the possible origins and factors of J–V hysteresis behavior in PSCs are focused and the strategies to suppress the hysteresis are summarized. Finally, insights on the future development of the J–V hysteresis in PSCs are also provided.

The power conversion efficiency (PCE) of perovskite solar cells (PSCs) has exceeded 25%, showing great potential in the photovoltaic field. However, PSCs often show anomalous current density–voltage (J–V) hysteresis behavior in the forward and reverse scanning directions, which makes it impossible to accurately evaluate the performance of PSCs. Therefore, it is necessary to clearly understand the mechanism of hysteresis and suppress the hysteresis. Herein, the J–V hysteresis behavior in PSCs and strategies to suppress hysteresis is focused: first, the various factors that affect J–V hysteresis in PSCs are summarized. And the mechanism behind the various possible origins of hysteresis and the challenges encountered are explored. Then, the strategies to suppress or eliminate the hysteresis are summarized, including optimizing the perovskite light‐absorbing layer, improving the performance of the carrier transport layer and interface engineering. Finally, insights on the future development of the hysteresis are also provided.

Herein, a one‐step solution‐processing of [MA_0.9Cs_0.1Pb(I_0.6Br_0.4)₃] wide‐bandgap perovskite using phenylhydrazine iodide with amino groups to successfully passivate the trap density within grain boundaries and increase the perovskite grain size is demonstrated. The reinforced morphology and grain boundaries treatment considerably enhance the power conversion efficiency from 12.16% for pristine to 14.63% for the treated devices.

Due to the attraction of fabricating highly efficient tandem solar cells, wide‐bandgap perovskite solar cells (PSCs) have attracted substantial interest in recent years. However, polycrystalline perovskite thin‐films show the existence of trap states at grain boundaries which diminish the optoelectronic properties of the perovskite and thus remains a challenge. Here, a one‐step solution‐processing of [ MA0.9Cs0.1Pb(I0.6Br0.4)3] wide‐bandgap perovskite using phenylhydrazine iodide with amino groups is demonstrated to successfully passivate the trap density within grain boundaries and increase the perovskite grain size. The reinforced morphology and grain boundaries treatment considerably enhanced the power conversion efficiency (PCE) from 12.16% for pristine to 14.63% for the treated devices. This strategy can be easily adopted to other perovskites and help realize highly efficient perovskite solar cells.

Tandem solar cells that pair silicon with a metal halide perovskite are a promising option for surpassing the single-cell efficiency limit. We report a monolithic perovskite/silicon tandem with a certified power conversion efficiency of 29.15%. The perovskite absorber, with a bandgap of 1.68 electron volts, remained phase-stable under illumination through a combination of fast hole extraction and minimized nonradiative recombination at the hole-selective interface. These features were made possible by a self-assembled, methyl-substituted carbazole monolayer as the hole-selective layer in the perovskite cell. The accelerated hole extraction was linked to a low ideality factor of 1.26 and single-junction fill factors of up to 84%, while enabling a tandem open-circuit voltage of as high as 1.92 volts. In air, without encapsulation, a tandem retained 95% of its initial efficiency after 300 hours of operation.

Publication date: March 2021

Source: Nano Energy, Volume 81

Author(s): Chengxi Zhang, Yan-Na Lu, Wu-Qiang Wu, Lianzhou Wang

A low‐temperature solution‐processed, annealing‐free, amorphous metal oxyhydroxide cathode interlayer is used to facilitate charge extraction and suppress interfacial charge recombination in inverted perovskite photovoltaics, delivering a power conversion efficiency of 21.3%.

The state‐of‐the‐art high‐performance perovskite solar cells (PSCs) with inverted p‐i‐n device structure normally use crystalline metal oxide materials or organic small molecules as the cathode interlayer between the fullerene layer and metal electrode. However, these interlayers are made by either high‐temperature or complicated vacuum‐assisted fabrication process, and in many cases, they are not efficient and effective enough to simultaneously extract the electrons and suppress the interfacial charge recombination. Herein, for the first time, a facile low‐temperature solution‐processed strategy is demonstrated to fabricate an amorphous metal oxyhydroxide (a‐MOH) thin film, which is used as a robust cathode interlayer in inverted PSCs. The a‐MOH interlayer not only facilitates electron extraction and collection via “energy‐favorable” electron tunneling, but also suppresses the interfacial charge recombination via effective hole blocking and electron backflow inhibition. As a result, the PSCs based on a‐MOH interlayer achieve a stabilized power conversion efficiency (PCE) of 21.1% and retain 93% of initial PCE after continuous one‐sun illumination for 500 hours.

A C₃N₄ layer functionalized with thiazole is introduced to the electron transfer layer/perovskite interface, which serves as an intermediate energy level to constitute a stepwise energy band alignment and donates the lone pair electrons to undercoordinated Pb²⁺. Resultantly, it effectively passivates the interfacial defects and promotes carrier transport, thereby further boosting the efficiency of the device.

Despite the conspicuous achievements in perovskite solar cells (PSCs), further improvement of the power conversion efficiency (PCE) is hindered by substantially detrimental carrier recombination resulting from the high interfacial charge defect density and inferior charge transport kinetics. Herein, an interface engineering strategy is developed to introduce a Lewis base thiophene or thiazole–modified C₃N₄ layer at the electron transfer layer (ETL)/perovskite interface to constitute a stepwise energy band alignment and passivate defects at interfaces of the perovskite film. Attributed to its well‐matched energy level with TiO₂ and perovskite, the charge extraction efficiency and charge transfer dynamics can be promoted remarkably, greatly inhibiting charge recombination at the interface. Furthermore, thiophene and thiazole can donate the lone pair electrons in S or N atoms to undercoordinated Pb²⁺, which effectively passivates the electronic trap states caused by halogen vacancies, thereby greatly minimizing trap‐assisted nonradiative recombination in the PSCs. Eventually, the thiazole–C₃N₄/perovskite‐based devices acquire an outstanding efficiency of 19.23%, supported by an enhanced open‐circuit voltage (V _OC) of 1.11 V with improved moisture stability. This work provides an avenue for interfacial energy level modulation and defect passivation strategies for a rational interface microstructure design for meliorating the performance of PSCs.

Publication date: March 2021

Source: Nano Energy, Volume 81

Author(s): Yutong Ren, Ming Ren, Xinrui Xie, Jianan Wang, Yaohang Cai, Yi Yuan, Jing Zhang, Peng Wang