JIALINGBO

The possible side reaction in the lead iodide solution of formamidinium is studied, and phenylboric acid (PBA) is introduced as a stabilizer in the perovskite precursor solution, which can inhibit the side reaction, thus greatly improving the stability of the perovskite solar cell.

The instability of the perovskite precursor solution seriously affects the purity of the perovskite films, which is one of the key factors for the low reproducibility for highly efficient devices. Formamidinium‐based perovskite with more suitable spectral absorption range and higher thermal stability has become the mainstream material. However, the side reactions in pure formamidinium lead iodide solution have not been fully revealed. Herein, it is demonstrated that self‐condensation of formamidinium iodide occurs to form the by‐product s‐triazine, and its content increases with the aging time of the solution. It is also discovered that phenylboric acid (PBA) can effectively inhibit the self‐condensation reaction and the content of the s‐triazine is decreased by more than 95% in the solution aging at 60 °C for 7 days. The PBA used as the stabilizer not only enhances purity and decreases defect density of the perovskite films but also strongly enhances the reproducibility for highly efficient perovskite solar cells.

Recent progress concerning the uses of carbon nanotubes (CNTs) as transparent conductive electrodes, charge‐transporter, perovskite additives, interlayers, hole‐transporting materials, and back electrodes in perovskite solar cells (PSCs) is reviewed. The application of CNTs toward the development of 1D and 2D flexible PSCs is discussed. Current challenges and prospective on research directions of employing CNTs to realize high‐performance PSCs is presented.

Abstract

Metal halide perovskite solar cells (PSCs) have emerged as promising next‐generation photovoltaic devices with the maximum output efficiency exceeding 25%. Despite significant advances, there are many challenges to achieve high efficiency, stability, and low‐cost simultaneously. Combating these challenges depends on developing novel materials and modifying conventional device components. Carbon nanotubes (CNTs) have attracted considerable attention for fabricating efficient PSCs owing to their remarkable electrical, optical, and mechanical properties. With their multifunctional features, CNTs can play a wide range of roles and offer unique benefits in various components in PSCs to improve device performance and durability. Here, recent progress concerning the utilizations of CNTs as transparent conductive electrodes, charge‐transporter, perovskite additives, interlayers, hole‐transporting materials, and back electrodes in PSCs is comprehensively reviewed. The application of CNTs toward the development of 1D and 2D flexible PSCs is also discussed. A summary of current challenges and prospective on future research directions of employing CNTs to realize high‐performance PSCs is presented.

A practical and straightforward method to reduce the defects of polycrystalline perovskite films is exploited by introducing functional fluorinated molecules at two different stages of film formation. The PSCs based on the DP strategy can simultaneously improve device performance and stability by effectively inhibiting the formation of superoxide species due to minimized defects at the perovskite surface and GBs.

Abstract

In recent years, the power conversion efficiency (PCE) of perovskite solar cells (PSCs) has witnessed rapid progress. Nevertheless, the pervasive defects prone to non‐radiative recombination and decomposition exist at the surface and the grain boundaries (GBs) of the polycrystalline perovskite films. Herein, we report a comprehensive dual‐passivation (DP) strategy to effectively passivate the defects at both surface and GBs to enhance device performance and stability further. Firstly, a fluorinated perylene‐tetracarboxylic diimide derivative is permeated in the perovskite metaphase during antisolvent treatment, and then a fluorinated bulky aromatic ammonium salt is introduced over the annealed perovskite. The reduction of defect density can be unambiguously proved by the superoxide species generation/quenching reaction. As a result, optimized planar PSCs demonstrate a decreased open‐circuit voltages deficit from 0.47 to 0.39 V and the best efficiency of 23.80 % from photocurrent scanning with a stabilized maximum power output efficiency of 22.99 %. Without encapsulation, one typical device can maintain over 85 % of the initial efficiency after heating on a hot plate at 100 °C for 30 h under relative humidity (RH) of 70 %. When the device is aged under 30±5 % RH, over 97 % of its initial PCE is retained after 1700 h.

In the past decade, the perovskite solar cell (PSC) has attracted tremendous attention. The electron transport layer (ETL) is one of the most important functional layers in PSCs. This review provides an up‐to‐date summary of the developments in inorganic electron transport materials for PSCs. Strategies to optimize the ETL, an outlook on current challenges and further development are discussed.

Abstract

In the past decade, the perovskite solar cell (PSC) has attracted tremendous attention thanks to the substantial efforts in improving the power conversion efficiency from 3.8% to 25.5% for single‐junction devices and even perovskite‐silicon tandems have reached 29.15%. This is a result of improvement in composition, solvent, interface, and dimensionality engineering. Furthermore, the long‐term stability of PSCs has also been significantly improved. Such rapid developments have made PSCs a competitive candidate for next‐generation photovoltaics. The electron transport layer (ETL) is one of the most important functional layers in PSCs, due to its crucial role in contributing to the overall performance of devices. This review provides an up‐to‐date summary of the developments in inorganic electron transport materials (ETMs) for PSCs. The three most prevalent inorganic ETMs (TiO₂, SnO_2, and ZnO) are examined with a focus on the effects of synthesis and preparation methods, as well as an introduction to their application in tandem devices. The emerging trends in inorganic ETMs used for PSC research are also reviewed. Finally, strategies to optimize the performance of ETL in PSCs, effects the ETL has on J–V hysteresis phenomenon and long‐term stability with an outlook on current challenges and further development are discussed.

The excited state characteristics of organic hole transport materials in perovskite photovoltaics (PVs), such as transition dipole moment, is confirmed to be a critical factor in improving the built‐in potential of devices for efficient charge extraction along with reduced carrier recombination. Moreover, the aggregation property of the organic semiconductor can have a synergistic effect with its excited state property for high‐efficiency perovskite PVs.

Abstract

Intrinsic characteristics of organic semiconductor‐based hole transport materials (HTMs) such as facile synthesizability, energy level tunability, and charge transport capability have been highlighted as crucial factors determining the performances of perovskite photovoltaic (PV) cells. However, their properties in the excited state have not been actively studied, although PVs are operated under solar illumination. Here, the characteristics of organic HTMs in their excited state such as transition dipole moment can be a decisive factor that can improve built‐in potential of PVs, consequently enhancing their charge extraction property as well as reducing carrier recombination. Moreover, the aggregation property of organic semiconductors, which has been an essential factor for high‐performance organic HTMs to improve their carrier transport property, can induce a synergistic effect with their excited state property for the high‐efficiency perovskite PVs. Additionally, it is also confirmed that their optical bandgaps, manipulated to have their absorption in the UV region, are beneficial to block UV light that degrades the quality of perovskite, consequently improving the stability of perovskite PV in p–i–n configuration. As a proof‐of‐concept, a model system, composed of triarylamine and imidazole‐based organic HTMs, is designed, and it is believed that this strategy paves a way toward high‐performance and stable perovskite PV devices.

Metal‐free halide perovskites have recently emerged as novel lightweight semiconductors for the next‐generation optoelectronics. In this review, research progress in metal‐free perovskites is summarized in terms of crystal structure and synthesis of these materials together with the various properties that are studied. Future prospects are further discussed to stimulate interest for optoelectronic and energy‐related areas.

Abstract

Even though the metal‐halide perovskites are attracting ever‐increasing interest for their breakthrough efficiencies in photovoltaics, light‐emitting diodes (LED), X‐ray imaging, and general optoelectronics, it was not until very recently that metal‐free halide perovskites become recognized, not only for their good optoelectronic performance, but also for their wide chemical diversity, tunability, lightweight, mechanical flexibility, and eco‐friendly processability. The community is turning their attention to these lightweight semiconductors, and promising results have been achieved in the initial evaluation of crystal structure and a range of properties including ferroelectric and optoelectronic properties. In this review, the crystal structure and synthesis of these materials are discussed together with the various properties that have been studied for these materials. Future prospects are further discussed for chemical diversity, structure tunability, synthetic process, potential properties, optoelectronic, and energy‐related applications.

4‐Dimethylaminopyridine (DMAP) is introduced to develop a facile technique for selectively passivating grain boundaries (GB) and controlling the topographical boundary of perovskite surfaces near GBs. A power conversion efficiency of 22.4% is achieved for a planar perovskite solar cell with DMAP treatment and the device stability under damp‐heat and light irradiation is improved.

Abstract

Recent progress in highly efficient perovskite solar cells (PSCs) has been made by virtue of interfacial engineering on 3D perovskite surfaces for their defect control, however, the structural stability of the modified interface against external stimuli still remains unresolved. Herein, 4‐dimethylaminopyridine (DMAP) is introduced to develop a facile technique for selectively passivating the grain boundary (GB) and controlling the topographical boundary of the perovskite surface near the GB. Through the surface treatment of DMAP, strongly bound DMAP crystals are selectively formed at the GB, which serves two functions: nonradiative recombination at GB is effectively reduced by healing the uncoordinated Pb²⁺ while adhesion strength between the perovskite and the poly(triaryl amine) (PTAA) polymer is significantly enhanced by a mechanical interlock effect. A planar PSC with DMAP treatment exhibits a champion power conversion efficiency of 22.4%, which is not only much higher than the 20.04% observed for a nontreated control device, but also the highest among the planar PSCs using PTAA polymers as a hole transport material. Furthermore, the use of DMAP leads to a substantial improvement in the device stability under damp‐heat test and light irradiation.

Novel interface polarization induced field‐effect passivation based on amorphous transition metal oxide is developed for efficient and ambient‐air‐stable perovskite solar cells. Comprehensive insights into the interaction between the field‐effect passivation, interface polarities, and the performance of the device have been elucidated in detail.

Abstract

Organolead halide hybrid perovskite solar cells (PSCs) have become a shining star in the renewable devices field due to the sharp growth of power conversion efficiency; however, interfacial recombination and carrier‐extraction losses at heterointerfaces between the perovskite active layer and the carrier transport layers remain the two main obstacles to further improve the power conversion efficiency. Here, novel field‐effect passivation has been successfully induced to effectively suppress the interfacial recombination and improve interfacial charge transfer by incorporating interfacial polarization via inserting a high work function interlayer between perovskite and holes transport layer. The charge dynamics within the device and the mechanism of the field‐effect passivation are elucidated in detail. The unique interfacial dipoles reinforce the built‐in field and prevent the photogenerated charges from recombining, resulting in power conversion efficiency up to 21.7% with negligible hysteresis. Furthermore, the hydrophobic interlayer also suppresses the perovskite decomposition by preventing the moisture penetration, thereby improving the humidity stability of the PSCs (>91% of the initial power conversion efficiency (PCE) after 30 d in 65 ± 5% humidity). Finally, several promising research perspectives based on field‐effect passivation are also suggested for further conversion efficiency improvements and photovoltaic applications.

The introduction of an appropriate passivating agent into the perovskite film is an effective technique for preventing the halide migration of mixed‐halide perovskites to develop high‐performance blue perovskite light emitting diodes (PeLEDs) with spectral stability. The PeLED with 60% diphenylpropylammonium chloride shows stable emission in the deep‐blue spectral region (464 nm) with a maximum external quantum efficiency of 1.92%.

Abstract

Blue emissive perovskites can be prepared by incorporating chlorine into bromine‐based perovskites to tune their bandgap. However, mixed‐halide perovskites exhibit intrinsic phase instability, particularly under electrical potential, owing to halide migration. To achieve high‐performance blue perovskite‐based light‐emitting diodes (PeLEDs) with operational stability, organic ammonium cations are used for passivating the anionic defects of the CsPbBr₂Cl film. Diphenylpropylammonium chloride (DPPACl), used as a passivating agent, successfully prevents the spectral instability of blue PeLEDs by passivating the Cl⁻ vacancies. Consequently, the blue PeLED prepared with this passivating agent delivers excellent device performance with a maximum external quantum efficiency of 3.03%. Moreover, upon tuning the DPPACl concentration, the PeLED emits stably in the deep‐blue spectral region (464 nm) with a half‐life time of 420 s. Thus, the use of organic ammonium cation as a passivating agent is an effective strategy for developing high‐performance blue PeLEDs with operational stability.

Smaller cations and anions are incorporated into FAPbI₃ single crystal to release its lattice stress and enhance its stability. The formed inch‐sized triple‐cation mixed‐halide perovskite single crystals exhibit suppressed ion migration, long carrier diffusion length, large mobility, and excellent uniformity. These superior properties are utilized for the construction of a high‐performance X‐ray detector array, realizing high‐contrast X‐ray imaging.

Abstract

Low ionic migration is required for a semiconductor material to realize stable high‐performance X‐ray detection. In this work, successful controlled incorporation of not only methylammonium (MA⁺) and cesium (Cs⁺) cations, but also bromine (Br^–) anions into the FAPbI₃ lattice to grow inch‐sized stable perovskite single crystal (FAMACs SC) is reported. The smaller cations and anions, comparing to the original FA⁺ and I^– help release lattice stress so that the FAMACs SC shows lower ion migration, enhanced hardness, lower trap density, longer carrier lifetime and diffusion length, higher charge mobility and thermal stability, and better uniformity. Therefore, X‐ray detectors made of the superior FAMACs SCs show the highest sensitivity of (3.5 ± 0.2) × 10⁶ μC Gy_air ⁻¹ cm⁻², about 29 times higher than the latest record of 1.22 × 10⁵ μC Gy_air ⁻¹ cm⁻² for polycrystalline MAPbI₃ wafer under the same 40 keV X‐ray radiation. Furthermore, the FAMACs SC X‐ray detector shows a low detection limit of 42 nGy s⁻¹, stable dark current, and photocurrent response. Finally, it is demonstrated that high contrast X‐ray imaging is realized using the FAMACs SC detector. The effective triple‐cation mixed halide strategy and the high crystalline quality make the present FAMACs SCs promising for next‐generation X‐ray imaging systems.

In recent years, the power conversion efficiency (PCE) of perovskite solar cells (PSCs) has witnessed rapid progress. Nevertheless, the pervasive defects prone to non‐radiative recombination and decomposition exist at the surface and the grain boundaries (GBs) of the polycrystalline perovskite films. Herein, we report a comprehensive dual‐passivation (DP) strategy to effectively passivate the defects at both surface and GBs to enhance device performance and stability further. Firstly, a fluorinated perylene‐tetracarboxylic diimide derivative is permeated in the perovskite metaphase during antisolvent treatment, and then a fluorinated bulky aromatic ammonium salt is introduced over the annealed perovskite. The reduction of defect density can be unambiguously proved by the superoxide species generation/quenching reaction. As a result, optimized planar PSCs demonstrate a decreased open‐circuit voltages deficit from 0.47 to 0.39 V and the best efficiency of 23.80% from photocurrent scanning with a stabilized maximum power output efficiency of 22.99%. Without encapsulation, one typical device can maintain over 85% of the initial efficiency after heating on a hot plate at 100 °C for 30 h under relative humidity (RH) of 70%. When the device is aged under 30 ± 5% RH, over 97% of its initial PCE is retained after 1700 h.

Publication date: 20 January 2021

Source: Joule, Volume 5, Issue 1

Author(s): Tianqi Niu, Weiya Zhu, Yiheng Zhang, Qifan Xue, Xuechen Jiao, Zijie Wang, Yue-Min Xie, Ping Li, Runfeng Chen, Fei Huang, Yuan Li, Hin-Lap Yip, Yong Cao

High performance perovskite solar modules (PSMs) are fabricated by introducing NH₄Cl to induce the formation of the intermediate phases. The PSMs show long‐term operational stability with a T ₈₀ lifetime under continuous light illumination exceeding 1600 h for a 5 × 5 cm² solar module and 1100 h for a 10 × 10 cm² solar module.

Abstract

In addition to high efficiencies, upscaling and long‐term operational stability are key pre‐requisites for moving perovskite solar cells toward commercial applications. In this work, a strategy to fabricate large‐area uniform and dense perovskite films with a thickness over one‐micrometer via a two‐step coating process by introducing NH₄Cl as an additive in the PbI₂ precursor solution is developed. Incorporation of NH₄Cl induces the formation of the intermediate phases of x[NH₄ ⁺]·[PbI₂Cl _x ] ^{x −} and HPbI_{3− x} Cl _x , which can effectively retard the crystallization rate of perovskite leading to uniform and compact full‐coverage perovskite layers across large areas with high crystallinity, large grain sizes, and small surface roughness. The 5 × 5 and 10 × 10 cm² perovskite solar modules (PSMs) based on this method achieve a power conversion efficiency (PCE) of 14.55% and 10.25%, respectively. These PSMs also exhibit good operational stability with a T ₈₀ lifetime (the time during which the solar module PCE drops to 80% of its initial value) under continuous light illumination exceeding 1600 h (5 × 5 cm²) and 1100 h (10 × 10 cm²), respectively.

The addition of the correct amounts of dimethyl sulfoxide (DMSO) with 2‐methoxyethanol (2‐ME) perovskite precursor ink is a crucial step toward reproducible slot‐die coatings and highly efficient perovskite solar cells. Through observing the drying process of 2ME‐DMSO inks from in situ X‐ray diffraction experiments, it is demonstrated that 11.77 mol% DMSO favorably affects thin film growth.

Abstract

Solar cells incorporating metal‐halide perovskite (MHP) semiconductors are continuing to break efficiency records for solution‐processed solar cell devices. Scaling MHP‐based devices to larger area prototypes requires the development and optimization of scalable process technology and ink formulations that enable reproducible coating results. It is demonstrated that the power conversion efficiency (PCE) of small‐area methylammonium lead iodide (MAPbI₃) devices, slot‐die coated from a 2‐methoxy‐ethanol (2‐ME) based ink with dimethyl‐sulfoxide (DMSO) used as an additive depends on the amount of DMSO and age of the ink formulation. When adding 12 mol% of DMSO, small‐area devices of high performance (20.8%) are achieved. The effect of DMSO content and age on the thin film morphology and device performance through in situ X‐ray diffraction and small‐angle X‐ray scattering experiments is rationalized. Adding a limited amount of DMSO prevents the formation of a crystalline intermediate phase related to MAPbI₃ and 2‐ME (MAPbI₃‐2‐ME) and induces the formation of the MAPbI₃ perovskite phase. Higher DMSO content leads to the precipitation of the (DMSO)₂MA₂Pb₃I₈ intermediate phase that negatively affects the thin‐film morphology. These results demonstrate that rational insights into the ink composition and process control are critical to enable reproducible large‐scale manufacturing of MHP‐based devices for commercial applications.

A low‐cost industrial organic pigment, quinacridone (QA), was applied as surface passivation agent for perovskite solar cells (PSCs) by solution processing of a soluble QA derivative followed by thermal annealing to convert it into insoluble QA. Passivation with strong interactions between QA molecules and metal halides, together with the hydrophobicity of QA coating, enabled highly efficient PSCs with remarkable stability.

Abstract

Surface passivation of perovskite solar cells (PSCs) using a low‐cost industrial organic pigment quinacridone (QA) is presented. The procedure involves solution processing a soluble derivative of QA, N,N‐bis(tert‐butyloxycarbonyl)‐quinacridone (TBOC‐QA), followed by thermal annealing to convert TBOC‐QA into insoluble QA. With halide perovskite thin films coated by QA, PSCs based on methylammonium lead iodide (MAPbI₃) showed significantly improved performance with remarkable stability. A PCE of 21.1 % was achieved, which is much higher than 18.9 % recorded for the unmodified devices. The QA coating with exceptional insolubility and hydrophobicity also led to greatly enhanced contact angle from 35.6° for the pristine MAPbI₃ thin films to 77.2° for QA coated MAPbI₃ thin films. The stability of QA passivated MAPbI₃ perovskite thin films and PSCs were significantly enhanced, retaining about 90 % of the initial efficiencies after more than 1000 hours storage under ambient conditions.

Crystalline, dense and uniform perovskite thin films are crucial for achieving high power conversion efficiency solar cells. Here, we demonstrated a universal method of fabricating highly crystalline and large‐grain perovskite films via crystal engineering. We applied anion exchange of Cl⁻ and I⁻, and annealing perovskite films, in an ultra‐confined and uniform temperature enclosed space with saturated MAI (or FAI) vapor using hot‐pressing sublimation technology. This process ensures a rapid crystal growth rate due to fast exchange between the gas phase and the crystalline film to reduce vertically oriented grain boundaries. The generation of the commonly observed PbI₂ phase is also suppressed due to the chemical equilibrium state during the thermal annealing process. Using this approach, pinhole‐free perovskite films with preferred crystal orientation and micrometer‐scale grains were obtained, leading to a high steady‐state efficiency of 22.15% based on mixed cation perovskite composition. In addition, devices based on different perovskite compositions all exhibited enhanced photovoltaic performance based on the crystal engineering method. The device (without encapsulation) had an efficiency loss of about only 4% after 2520‐hour aging in ambient conditions and retained 87% of its initial efficiency after 1000‐hour continuous one‐sun light soaking, thus demonstrating considerably improved stability.

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The detailed crystallization pathways of perovskite film manipulated by Lewis base additives are investigated using in situ grazing‐incidence wide‐angle scattering. The modulated crystallization process can be attributed to the intermolecular interaction between Lewis base molecules and perovskite precursors, which results in reduced defect density and ameliorative carrier behavior in high‐crystalline perovskite film as well as the elevated photovoltaic performance.

Abstract

The Lewis acid–base adduct approach has been widely used to form high‐crystalline perovskite films, but the complicated crystallization pathway and underlying film formation mechanism are still ambiguous. Here, the detailed crystallization process of perovskites manipulated by Lewis base additives has been revealed by in situ X‐ray scattering measurements. Through monitoring the film formation process, two distinct crystal growth stages have been definitely recognized: i) an intermediate phase‐dominated stage; and ii) a phase transformation stage from intermediates to crystalline perovskite phase. Incorporating Lewis base additives significantly prolongs the duration of stage 1 and induces a postponed phase transformation pathway, which could be responsible for retardant crystallization kinetics. Based on a series of experimental results and theoretical calculations, it is indicated that the manipulation of perovskite crystallization pathway is a result of the modulated molecular interactions between Lewis base additives and solution precursors. Owing to the retardant crystallization kinetics, enhanced‐quality perovskite films with reduced defect density and improved optoelectronic properties, as well as optimized photovoltaic performance have been demonstrated. This work provides in‐depth understanding with respect to perovskite crystallization pathway modulated by Lewis base additives and perceptive guidelines for precise regulation of crystallization kinetics of perovskite film toward high performance.

It is critical to understand how metal halide perovskite solar cells behave under reverse bias. Herein, it is shown that the power conversion efficiency losses after prolonged reverse bias are due to accumulation of holes within the bulk perovskite. Consequently, determinantal electrochemical oxidation reactions occur in the bulk, resulting in increased recombination and halide/halogen diffusion into charge transport layers.

Abstract

Partial shading of a solar module can induce a set of cells within the module to operate under reverse bias. Studies have shown that metal halide perovskite solar cells with a wide variety of compositions and contacts exhibit interesting behavior in reverse bias that includes both reversible performance loss and non‐reversible degradation. In this paper, an advanced drift‐diffusion approach incorporating an electrochemical term to explain the short‐circuit, open circuit and fill factor losses that are experimentally measured after prolonged reverse bias is used. It is shown that holes can tunnel into the perovskite due to sharp band bending near the contact, accumulate within the bulk of the perovskite absorber, and trigger the oxidation of halides to form neutral halogens. The density of neutral halogens is much higher in reverse bias because there are hardly any electrons available to reduce the iodine. The resulting halogens act as bulk recombination centers. While the interstitial halogen density does decay when the cell is operated in forward bias, permanent degradation can occur if the iodine diffuses out of the perovskite layer. Finally, the ways in which changing parameters such as the mobile ion density or the series resistance at the contact can influence device performance and stability are discussed.

Low conductivity and hole mobility in the pristine metal phthalocyanines greatly limit their application in perovskite solar cells (PSCs) as the hole‐transporting materials (HTMs). Here, we prepare a Ni phthalocyanine (NiPc) decorated by four methoxyethoxy units as HTMs. In NiPc, the two oxygen atoms in peripheral substituent have a modified effect on the dipole direction, while the central Ni atom contributes more electron to phthalocyanine ring, thus efficiently increasing the intramolecular dipole. Calculation analyses reveal the extracted holes within NiPc are mainly concentrated on the phthalocyanine core induced by the intramolecular electric field, and further to be transferred by π‐π stacking space channel between NiPc molecules. Finally, the best efficiency of PSCs with NiPc as dopant‐free HTs realizes a record value of 21.23% (certified 21.03%). The PSCs also exhibit the good moisture, heating and light stabilities. This work provides a novel way to improve the performance of PSCs with free‐doped metal phthalocyanines as HTMs.

Polymer passivation layers can improve the open-circuit voltage of perovskite solar cells when inserted at the perovskite–charge transport layer interfaces. Unfortunately, many such layers are poor conductors, leading to a trade-off between passivation quality (voltage) and series resistance (fill factor, FF). Here, we introduce a nanopatterned electron transport layer that overcomes this trade-off by modifying the spatial distribution of the passivation layer to form nanoscale localized charge transport pathways through an otherwise passivated interface, thereby providing both effective passivation and excellent charge extraction. By combining the nanopatterned electron transport layer with a dopant-free hole transport layer, we achieved a certified power conversion efficiency of 21.6% for a 1-square-centimeter cell with FF of 0.839, and demonstrate an encapsulated cell that retains ~91.7% of its initial efficiency after 1000 hours of damp heat exposure.

Bromide‐based organo‐metal halide perovskites have shown great potential for use in tandem solar cells, LEDs and photodetectors. Here, we report a new protocol using a one‐step deposition method for producing formamidinium lead bromide (FAPbBr₃) perovskites, which features a solvent engineered intermediate phase to achieve superior films. For the first time, an FABr‐PbBr₂‐DMSO intermediate is identified and single crystals of the same intermediate compound have been synthesized. A systematic investigation of phase evolution in the film formation process reveals that DMSO enables crystallization of the FABr‐PbBr₂‐DMSO intermediate, and thus modulates the crystallization process of FAPbBr₃ perovskite, achieving uniform, smooth films with Volmer–Weber morphology. To prevent hole leakage arising from the larger bandgap of FAPbBr₃ than FAPbI₃, we added an additional layer of Mg‐doped ZnO nanoparticles. As a result, inverted solar cells using these solvent engineered films can achieve power conversion efficiencies (PCEs) of up to 9.06 %, the highest reported efficiency for inverted FAPbBr₃ perovskite devices.

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Publication date: May 2021

Source: Nano Energy, Volume 83

Author(s): Sergey Tsarev, Selina Olthof, Aleksandra G. Boldyreva, Sergey M. Aldoshin, Keith J. Stevenson, Pavel A. Troshin