JIALINGBO

Process dependent lead(II) iodide (PbI₂) formation is examined on the surfaces of FAPbI₃(formamidinium lead triiodide) films. Due to the faster evaporation rate of organic substances, crystalline PbI₂ as an inclusion is found within the triple junction grain boundaries. Control of the vapor pressure can suppress the PbI₂ formation and enhance the stability by eliminating the degradation sites induced by the photoinstability of PbI₂.

Abstract

Excess lead(II) iodide (PbI₂) has controversial roles in affecting the efficiency of perovskite solar cells (PSCs). Since the photoinstability of PbI₂ is now known to largely accelerate perovskite degradation, suppressing and/or eliminating excess PbI₂ is key to improving the stability of PSCs. Herein, process-dependent PbI₂ formation on the surfaces of formamidinium lead triiodide (FAPbI₃) films is examined. Due to the faster evaporation rate of organic substances, crystalline PbI₂ as an inclusion is found within the triple junction grain boundaries. With this hypothesis, two strategies are suggested: control of the 1) vapor pressure and 2) stoichiometry of precursor solutions to induce sufficient reaction of FAPbI₃. Although both strategies successfully eliminate the PbI₂ as inclusions, due to the slower evaporation rate, vapor pressure control films also exhibit a larger grain size (≈1.18 µm) with a good film quality to attain the highest power conversion efficiency (PCE) of 24.5%. Furthermore, the phase stability of α-FAPbI₃ is improved due to the elimination of the degradation sites induced by the photoinstability of PbI₂. The findings explore the formation process of unwanted PbI₂ (≈2.8%) and provide a simple method to effectively suppress its formation. This may further boost the PCE and stability, especially for FA-based perovskites.

A deformable coumarin has been successfully employed to passivate anion/cation defects and release residual stress, endowing that phase segregation can be effectively inhibited. Moreover, the benefit of the larger grain size and less trap-assisted recombination, yielding an exceptional efficiency of over 24% for rigid inverted perovskite solar cells and an efficiency of over 23% for flexible inverted perovskite solar cells.

Abstract

The defects and phase segregation in perovskite will significantly reduce the performance and stability of perovskite solar cells (PSCs). In this work, a deformable coumarin is employed as a multifunctional additive for formamidinium–cesium (FA-Cs) perovskite. During the annealing process of perovskite, the partial decomposition of coumarin passivates the Pb²⁺, iodine, and organic cation defects. Additionally, coumarin can affect colloidal size distributions, resulting in relatively large grain size and good crystallinity of target perovskite film. Hence, the carrier extraction/transport can be promoted, trap-assisted recombination is reduced, and energy levels are optimized in target perovskite films. Furthermore, the coumarin treatment can significantly release residual stress. As a result, the champion power conversion efficiencies (PCEs) of 23.18% and 24.14% are obtained for Br-rich (FA_0.88Cs_0.12PbI_2.64Br_0.36) and Br-poor (FA_0.96Cs_0.04PbI_2.8Br_0.12) based devices, respectively. The flexible PSCs based on Br-poor perovskite exhibit an excellent PCE of 23.13%, one of the highest values for flexible PSCs reported to date. Due to the inhibition of phase segregation, the target devices exhibit excellent thermal and light stability. This work provides new insights into the additive engineering of passivating defects, stress relief, and inhibition of phase segregation of perovskite films, offering a reliable method to develop state-of-the-art solar cells.

A bowl (corannulene)-assisted ball (fullerene) assembly strategy for solution-processing the favorable C₆₀ electron transport layer (ETL) of perovskite solar cells (PSCs) was deliberately proposed, delivering a highest power conversion efficiency (PCE) of 21.7 % with an excellent light-soaking stability of 1000 hours, which highlights the great potential of corannulene in solubilizing and stabilizing C₆₀ for efficient and stable PSCs.

Abstract

Pristine fullerene C₆₀ is an excellent electron transport material for state-of-the-art inverted structure perovskite solar cells (PSCs), but its low solubility leaves thermal evaporation as the only method for depositing it into a high-quality electron transport layer (ETL). To address this problem, we herein introduce a highly soluble bowl-shaped additive, corannulene, to assist in C₆₀-assembly into a smooth and compact film through the favorable bowl-ball interaction. Our results show that not only corannulene can dramatically enhance the film formability of C₆₀, it also plays a critical role in forming C₆₀-corannulene (CC) supramolecular species and in boosting intermolecular electron transport dynamics in the ETL. This strategy has allowed CC devices to deliver high power conversion efficiencies up to 21.69 %, which is the highest value among the PSCs based on the solution-processed-C₆₀ (SP-C₆₀) ETL. Moreover, the stability of the CC device is far superior to that of the C₆₀-only device because corannulene can retard and curb the spontaneous aggregation of C₆₀. This work establishes the bowl-assisted ball assembly strategy for developing low-cost and efficient SP-C₆₀ ETLs with high promise for fully-SP PSCs.

A void-free buried interface in p-i-n-based FAPbI3 perovskite solar cells (PSCs) enables to upscale lab-scale solar cells (<1 cm²) to mini-module dimensions (>10 cm²). A combined strategy of vacuum-assisted growth, a moderate N2 flow, and MACl precursor in the crystallization of perovskite layers effectively eliminates interfacial voids as apparent in thin films processed by the anti-solvent method. 22.3% and 18.3% efficiencies are achieved for p-i-n-based additive-free FAPbI3 PSCs (0.105 cm2) and scalable mini-modules (aperture area 12.25 cm2), respectively.

Nature Energy, Published online: 12 June 2023; doi:10.1038/s41560-023-01274-z

Zhu et al. develop a low-cost donor–acceptor-type hole-selective layer that minimizes interfacial non-radiative charge recombination losses in single-junction and tandem solar cells based on metal halide perovskites with different bandgaps.

An organic small-molecule octafluoro-1,6-hexanediol diacrylate (OF-HDDA) is introduced to in situ crosslink forming a polymer (POF-HDDA), which anchors uncoordinated lead ions and prevents lead leakage from water and oxygen invasion, and concurrently improves the long-term stability of the corresponding devices.

Abstract

High-performance perovskite solar cells have demonstrated commercial viability, but still face the risk of contamination from lead leakage and long-term stability problems caused by defects. Here, an organic small molecule (octafluoro-1,6-hexanediol diacrylate) is introduced into the perovskite film to form a polymer through in situ thermal crosslinking, of which the carbonyl group anchors the uncoordinated Pb²⁺ of perovskite and reduces the leakage of lead, along with the −CF₂− hydrophobic group protecting the Pb²⁺ from water invasion. Additionally, the polymer passivates varieties of Pb-related and I-related defects through coordination and hydrogen bonding interactions, regulating the crystallization of perovskite film with reduced trap density, releasing lattice strain, and promoting carrier transport and extraction. The optimal efficiencies of polymer-incorporated devices are 24.76 % (0.09 cm²) and 20.66 % (14 cm²). More importantly, the storage stability, thermal stability, and operational stability have been significantly improved.

An additive strategy of using potassium formate (HCOOK) as an additive to suppress I₂ impurity defects and passivate perovskite defects is developed. Meanwhile, HCOOK also enlarges the grain size of perovskite, reduces the defects at grain boundaries as well as inhibits the migration of halide ions. The resultant planar n–i–p-structured PSCs exhibit impressive photovoltaic performance.

Abstract

The performance of perovskite solar cells (PSCs) is negatively affected by iodine (I₂) impurities generated from the oxidation of iodide ions in the perovskite precursor powder, solution, and perovskite films. In this study, the use of potassium formate (HCOOK) as a reductant to minimize the presence of detrimental I₂ impurities is presented. It is demonstrated that HCOOK can effectively reduce I₂ back to I⁻ in the precursor solution as well as in the devices under external conditions. Furthermore, the introduced formate anion (HCOO⁻) and alkali metal cation (K⁺) can reduce the defect density within the perovskite film by modulating perovskite growth and passivating electronic defects, significantly prolonging the carrier lifetime and reducing the J–V hysteresis. Consequently, the maximum efficiency of the HCOOK-doped planar n–i–p PSCs reaches 23.8%. After 1000 h of operation at maximum power point tracking under continuous 1 sun illumination, the corresponding encapsulated devices retain 94% of their initial efficiency.

A Lewis-base trans-Ferulic acid (t-FA) is introduced into ≈1.77 eV perovskite precursor solution. Larger perovskite crystals are formed, the residual microstrain is released, and the structure is stabilized with t-FA to inhibit light-induced halide segregation. The optimized device delivers a power conversion efficiency (PCE) of 19.9% and a V _OC of 1.32 V, among the highest performance reported in wide bandgap perovskite devices.

Abstract

Efficient and stable wide bandgap (WBG) perovskite solar cells (PSCs) are imperative for fabricating superior tandem devices. However, small crystal grains and light-induced phase segregation of WBG perovskite result in large open-circuit voltage (V _OC) deficits, critically impeding the development of the related devices. Herein, the effective functional groups of Lewis-base trans-Ferulic acid (t-FA) are employed to release the residual microstrain in the perovskite lattice. Larger perovskite crystals are formed by strengthening the interaction between the perovskite solute and solution. The lattice structure is stabilized to suppress light-induced halide segregation. Finally, the power conversion efficiency (PCE) of the optimized device with a bandgap of ≈1.77 eV is increased from 17.33% to 19.31% with the enhancement of V _OC. Moreover, replacing a mixture of MeO-2PACZ and Me-4PACZ as the hole transporting layer (HTL), the PCE further lifts to 19.9% and V _OC is 1.32 V, one of the highest performances reported for WBG PSCs, especially for devices prepared entirely by solution spin-coating. Therefore, this study provides a practicable alternative for realizing efficient WBG PSCs, which can contribute to the growth of perovskite-based tandem devices.

The formation of Pb–S bonds between perovskite and 2-mercapto-1-methylimidazole appreciably reduces surface trap and improves interfacial energy level alignment. The open circuit voltage of inverted inorganic perovskite solar cells is enhanced by 120 mV, yielding a power conversion efficiency of 20.6%, along with improved ambient stability.

Abstract

Due to their excellent thermal stability and ideal bandgap, metal halide inorganic perovskite based solar cells (PSCs) with inverted structure are considered as an excellent choice for perovskite/silicon tandem solar cells. However, the power conversion efficiency (PCE) of inverted inorganic perovskite solar cells (PSCs) still lags far behind that of conventional n–i–p PSCs due to interfacial energy level mismatch and high nonradiative charge recombination. Herein, the performance of inverted PSCs is significantly improved by interfacial engineering of CsPbI_{3− x} Br _x films with 2-mercapto-1-methylimidazole (MMI). It is found that the mercapto group can preferably react with the undercoordinated Pb²⁺ from perovskite by forming Pb–S bonds, which appreciably reduces the surface trap density. Moreover, MMI modification results in a better energy level alignment with the electron-transporting material, promoting carrier transfer and reducing voltage deficit. The above combination results in an open-circuit voltage enhancement by 120 mV, yielding a champion PCE of 20.6% for 0.09 cm² area and 17.3% for 1 cm² area. Furthermore, the ambient, operational and heat stabilities of inorganic PSCs with MMI modification are also greatly improved. The work demonstrates a simple but effective approach for fabricating highly efficient and stable inverted inorganic PSCs.

Perovskite phase-pure mixed-cation Cs _x MA_1−x PbI₃ nanocrystals were obtained by post-synthesis cation exchange between CsPbI₃ and MAPbI₃ nanocrystals at room temperature. The Cs _x MA_1−x PbI₃ nanocrystals exhibit composition-tunable photoluminescence (PL) with their thermal stability that is enhanced compared to the parent CsPbI₃ and MAPbI₃ nanocrystals.

Abstract

Cesium methylammonium lead iodide (Cs _x MA_1−x PbI₃) nanocrystals were obtained with a wide range of A-site Cs-MA compositions by post-synthetic, room temperature cation exchange between CsPbI₃ nanocrystals and MAPbI₃ nanocrystals. The alloyed Cs _x MA_1−x PbI₃ nanocrystals retain their photoactive perovskite phase with incorporated Cs content, x, as high as 0.74 and the expected composition-tunable photoluminescence (PL). Excess methylammonium oleate from the reaction mixture in the MAPbI₃ nanocrystal dispersions was necessary to obtain fast Cs-MA cation exchange. The phase transformation and degradation kinetics of films of Cs _x MA_1−x PbI₃ nanocrystals were measured and modeled using an Avrami expression. The transformation kinetics were significantly slower than those of the parent CsPbI₃ and MAPbI₃ nanocrystals, with Avrami rate constants, k, at least an order of magnitude smaller. These results affirm that A-site cation alloying is a promising strategy for stabilizing iodide-based perovskites.

Incorporation of a multifunctional liquid crystal (LQ) into (2,2′,7,7′-tetrakis(N,N-di-p-methoxyphenylamine)-9,9′-spirobifluorene (Spiro-OMeTAD)-based hole transport layer (HTL) of perovskite solar cells (PSCs) can strongly enhance hot carriers extraction/transfer from perovskite layer into HTL, reducing charge-carrier recombination in device. Moreover, LQ can efficiently prevent the Li ions migration and agglomeration of Lithium bis(trifluoromethanesulfonyl)imide (Li-TFSI) HTL dopant through chemical interaction. Using this approach, highly efficient and stable PSCs are achieved.

Abstract

Lithium bis(trifluoromethanesulfonyl)imide (Li-TFSI) has been identified as the most used and effective p-dopant for hole transport layer (HTL) in perovskite solar cells (PSCs). However, the migration and agglomeration of Li-TFSI in HTL negatively impact PSCs performance and stability. Herein, we report an effective strategy for adding a liquid crystal organic small molecule (LQ) into Li-TFSI doped (2,2′,7,7′-tetrakis(N,N-di-p-methoxyphenylamine)-9,9′- spirobifluorene (Spiro-OMeTAD) HTL. It was found that the introduction of LQ into Spiro-OMeTAD HTL can efficiently enhance the charge carrier extraction and transportation in device, which can strongly retard the charge carrier recombination in device. Consequently, the PSCs efficiency is significantly enhanced to 24.42 % (Spiro-OMeTAD+LQ) from 21.03 % (Spiro-OMeTAD). The chemical coordination between LQ and Li-TFSI can strongly confine Li⁺ ions migration and agglomeration of Li-TFSI, thus, achieving the enhanced device stability. Only a 9 % efficiency degradation is observed for un-encapsulated device prepared with Spiro-OMeTAD and LQ after 1700 h under air environment, while the efficiency drops by 30 % for the reference device. This work provides an effective strategy for improving the efficiency and stability of PSCs, and gives some important insights for understanding intrinsic hot carriers dynamics for perovskite-based optoelectronic devices.

A strategy for highly efficient and robust perovskite solar cells via a greenable slot-die process is reported. Locally supersaturated perovskite ink based on low-toxic dimethyl sulfoxide is prepared by rheological engineering with a small amount of 1,2-dichlorobenzene . The findings present a strategy for designing perovskite inks and a pathway toward the future commercialization of perovskite solar cells.

Abstract

Perovskite solar cells (PSCs), which debuted with a lot of attention based on high efficiency, are establishing as one of the most promising thin-film photovoltaic technologies. Currently, research for upscaling and commercialization through eco-friendly solvent and process systems is being attempted. This study introduces for the first time a rheological engineering-based locally supersaturated perovskite ink (LSPI) strategy for slot-die process-based PSC fabrication suitable for roll-to-roll continuous processes. Here, for the greenable slot-die process, a perovskite precursor ink composed of a low-toxic dimethyl sulfoxide (DMSO) single solvent is used and a small amount of 1,2-dichlorobenzene (DCB) is utilized as a modulator to control the rheological properties of the ink. The addition of DCB lowers the high surface tension of the DMSO-based perovskite precursor ink to suit the slot-die process, enabling uniform wet film formation, and produces locally supersaturated colloids, i.e., perovskite seeds, that help growth into dense and large grains by heterogeneous nucleation with low Gibbs-free energy. As a result, the LSPI enables slot-die coating-based PSCs with an efficiency of 20.61% (active areas of 0.1 cm²), which allow high efficiencies of 18.66% and 17.66% (active areas of 2.7 and 8.64 cm²) to be achieved in scale-up to minimodules, respectively.

Perovskite Solar Modules

In article number 2211593, Yang Wang, Yanlin Song, and co-workers propose a strategy of vapor-assisted defect passivation to manage defects in perovskite solar modules. CS₂ can strongly coordinate with undercoordinated Pb²⁺ and passivate iodide vacancy defects, resulting in remarkable enhancement of the device efficiency (25.20% for 0.08 cm² and 20.66% for 40.6 cm²).

The differences in energy yield and levelized cost of electricity between bifacial tandem photovoltaic (PV) modules and bifacial heterojunction PV modules under different outdoor conditions are compared. Herein, important implications for the selection of cost-effective PV module types are provided to generate renewable electricity.

Bifacial perovskite (PVK)/crystalline silicon (c-Si) tandem photovoltaic (PV) modules provide an effective strategy to further improve the efficiency and energy yield (EY) of c-Si PV modules. In this work, the energy outputs of bifacial tandem PV modules under outdoor conditions are analyzed by combining optical modeling, one-diode equivalent circuit model, module tilt angle, and meteorological data, and a detailed comparative study with bifacial silicon heterojunction (SHJ) PV modules is also performed. The bifacial PVK/c-Si tandem modules exhibit higher EY in locations with strong direct normal irradiance regardless of the ground type with any albedo, while bifacial SHJ modules exhibit similar or even higher EY than tandem modules in locations with strong diffuse horizontal irradiance (DHI) such as Chengdu. Considering factors such as EY and levelized cost of electricity, E _{g_PVK} in the range of 1.58–1.62 eV is suitable for most application scenarios, while the deployment of bifacial SHJ PV modules is preferred in areas dominated by DHI, as represented by Chengdu. Herein, important implications for policy making in determining the cost-effective type of PV modules are provided to generate renewable electricity.

Recent progress on organic interface modifiers (OIMs) is reported according to the following categories: the anchoring groups (metal oxide, perovskite, and organic material) and frameworks (backbone and spacer). Then various strategies and effects of properly designed OIMs are discussed. Finally, an outlook on the application of extended OIM technology for the future development of efficient and stable PSCs is provided.

Abstract

Perovskite solar cells (PSCs) have demonstrated rapid progress in their power conversion efficiencies (PCEs)—from 3.8% in 2009 to 25.7% in 2022—and they have received considerable attention as a promising future photovoltaic (PV) technology. However, the operational stability of PSCs is still inadequate to satisfy the standards for commercial applications. Interface engineering has become one of the most important strategies to push PSCs’ efficiency and stability for practical use. Among the various interface engineering approaches, organic interface modifiers (OIMs) have been frequently used by the PSC field to address the issues limiting PSC stability at high efficiency levels. In this perspective, the chemical structures of state-of-the-art OIMs are discussed, and their characteristics are reviewed, as well as the impact on device performance associated with key device interfaces (e.g., metal oxide/perovskite and organic transport layer/perovskite interfaces) from a chemical and materials engineering point of view is discussed. Design considerations and the authors' perspective are discussed, on the basis of representative literature examples, for building new, customized organic OIMs to further improve PSC efficiency and stability toward commercialization.

Using molecular self-assembly strategy effectively passivates the interfacial defects at the FAPbBr₃ film surface, resulting in enhancement of the photovoltaic performance of wide bandgap FAPbBr₃ perovskite, especially in low-light environments. More importantly, this report also demonstrates the considerable potential of FAPbBr₃ solar cells for underwater photovoltaic applications.

Abstract

Underwater solar cells (UWSCs) provide an ideal alternative to the energy supply for long-endurance autonomous underwater vehicles. However, different from conventional solar cells situated on land or above water, UWSCs give preference to use wide bandgap semiconductors (≥1.8 eV) as light absorber to match underwater solar spectra. Among wide bandgap semiconductors, FAPbBr₃ perovskite is under prime consideration owing to its matching optical bandgap (≈2.3 eV), outstanding photoelectric properties, easier processability, etc. Unfortunately, for FAPbBr₃ solar cells, substantial interface defects greatly limit the charge carrier extraction efficiency, thus limiting the device performance, especially in underwater low-light environments. This study employs a molecular self-assembly strategy to effectively eliminate the interfacial defects. As a result, a great improvement in power conversion efficiency (PCE) from 6.44% to 7.49% is obtained, which is among the best efficiency reported for inverted FAPbBr₃ solar cells up to date. Besides, a champion PCE of 30% is obtained under 520 nm monochromatic light irradiation (4.8 mW cm⁻²). These results demonstrate that FAPbBr₃ solar cells present a tremendously promising application in UWSCs.

Multiple iodine-related defects in CsPbI_3−x Br _x perovskite solar cells (PSCs) were inhibited by the synergistic effects of halogen, coordination, and hydrogen bonds of 2,6-diaminopyridine (2,6-DAPy). This results in an excellent power-conversion efficiency of 21.8 % for the 2,6-DAPy-CsPbI_3−x Br _x PSCs, alongside significantly enhanced humidity stabilities of unencapsulated cells.

Abstract

Halide-related surface defects on inorganic halide perovskite not only induce charge recombination but also severely limit the long-term stability of perovskite solar cells. Herein, adopting density functional theory calculation, we verify that iodine interstitials (I_i) has a low formation energy similar to that of the iodine vacancy (V_I) and is also readily formed on the surface of all-inorganic perovskite, and it is regarded to function as an electron trap. We screen a specific 2,6-diaminopyridine (2,6-DAPy) passivator, which, with the aid of the combined effects from halogen-N_pyridine and coordination bonds, not only successfully eliminates the I_i and dissociative I₂ but also passivates the abundant V_I. Furthermore, the two symmetric neighboring -NH₂ groups interact with adjacent halides of the octahedral cluster by forming hydrogen bonds, which further promotes the adsorption of 2,6-DAPy molecules onto the perovskite surface. Such synergetic effects can significantly passivate harmful iodine-related defects and undercoordinated Pb²⁺, prolong carrier lifetimes and facilitate the interfacial hole transfer. Consequently, these merits enhance the power-conversion efficiency (PCE) from 19.6 % to 21.8 %, the highest value for this type of solar cells, just as importantly, the 2,6-DAPy-treated CsPbI_3−x Br _x films show better environmental stability.

A novel surface passivator 2,4,6-trimethylbenzenaminium iodide (TMBAI) is developed and employed as the interfacial layer between the perovskite and hole transport layer to modify the surface defect states. The TMBAI-based PSCs showed excellent stability and demonstrated power conversion efficiencies of 23.7% (0.16 cm²) and 21.7% (1 cm²) under standard AM1.5 G sunlight, respectively.

Abstract

Surface defects cause non-radiative charge recombination and reduce the photovoltaic performance of perovskite solar cells (PSCs), thus effective passivation of defects has become a crucial method for achieving efficient and stable devices. Organic ammonium halides have been widely used for perovskite surface passivation, due to their simple preparation, lattice matching with perovskite, and high defects passivation ability. Herein, a surface passivator 2,4,6-trimethylbenzenaminium iodide (TMBAI) is employed as the interfacial layer between the spiro-OMeTAD and perovskite layer to modify the surface defect states. It is found that TMBAI treatment suppresses the nonradiative charge carrier recombination, resulting in a 60 mV increase of the open-circuit voltage (V _oc) (from 1.11 to 1.17 V) and raises the fill factor from 76.3% to 80.3%. As a result, the TMBAI-based PSCs device demonstrates a power conversion efficiency (PCE) of 23.7%. Remarkably, PSCs with an aperture area of 1 square centimeter produce a PCE of 21.7% under standard AM1.5 G sunlight. The unencapsulated TMBAI-modified device retains 92.6% and 90.1% of the initial values after 1000 and 550 h under ambient conditions (humidity 55%–65%) and one-sun continuous illumination, respectively.

A multifunctional nitrogen-heterocyclic ring molecule is introduced for controlled vertically orientation growth of 2D passivation layer on the surface of 3D perovskite film via multi-site intermolecular interactions. With suppressed trap-states density, prolonged charge carrier lifetime, and elevated charge extraction and transfer, an optimal power conversion efficiency  of 24.6% is achieved with improved stability.

Abstract

Surface passivation via 2D perovskite is critical for perovskite solar cells (PSCs) to achieve remarkable performances, in which the applied spacer cations play an important role on structural templating. However, the random orientation of 2D perovskite always hinder the carrier transport. Herein, multiple nitrogen sites containing organic spacer molecule (1H-Pyrazole-1-carboxamidine hydrochloride, PAH) is introduced to form 2D passivation layer on the surface of formamidinium based (FAPbI₃) perovskite. Deriving from the interactions between PAH and PbI₂, the defects of FAPbI₃ perovskite are effectively passivated. Interestingly, due to the multiple-site interactions, the 2D nanosheets are found to grow perpendicularly to the substrate for promotion of charge transfer. Therefore, an impressive power conversion efficiency of 24.6% and outstanding long-term stability are achieved for the 2D/3D perovskite devices. The findings further provide a perspective in structure design of novel organic halide salts for the fabrication of efficient and stable PSCs.

Nature Communications, Published online: 17 May 2023; doi:10.1038/s41467-023-38545-y

Efficient light extraction in perovskite X/γ-ray scintillators is hindered by the small Stokes shift of exciton luminescence. Here, Jin et al. exploit the intrinsic strain in 2D perovskite as “self-wavelength shifting” to reduce the self-absorption effect without sacrificing the device response speed.

The performance of inverted perovskite solar cells is enhanced due to: (1) Amino groups in 4-butanediol ammonium Bromide (BD) react with the disassortative lead ion and fill formamidinium ions vacancies in perovskite, resulting in enhanced perovskite crystallinity; (2) The formation of hydrogen bonds between poly [bis (4-phenyl) (2,4,6-triMethylphenyl) amine](PTAA) and BD molecules contributes to the improved surface contact of PTAA/perovskite.

Abstract

Inverted perovskite solar cells (IPSCs) have witnessed an impressive development in recent years. However, their efficiency is still significantly behind theoretical limits, and device instabilities hinder their commercialization. Two main obstacles to further enhancing their performance via one-step deposition are: 1) the unsatisfactory film quality of perovskite and 2) the poor surface contact. To address the above issues, 4-butanediol ammonium Bromide (BD) is utilized to passivate Pb²⁺ defects by forming PbN bonds and fill vacancies of formamidinium ions at the buried surface of perovskite. The wettability of poly [bis (4-phenyl) (2,4,6-triMethylphenyl) amine] films is also improved due to the formation of hydrogen bonds between PTAA and BD molecules, resulting in better surface contacts and enhanced perovskite crystallinity. As a result, BD-modified perovskite thin films show a significant increase in the mean grain size, as well as a dramatic enhancement in the PL decay lifetime. The BD-treated device exhibits an efficiency of up to 21.26%, considerably higher than the control device. Moreover, the modified devices show dramatically enhanced thermal and ambient stability compared to the control ones. This methodology paves the way to obtain high-quality perovskite films for fabricating high-performance IPSCs.

Buried interface passivation is very important for the power conversion efficiency (PCE) breakthrough and stability improvement of perovskite solar cells (PSCs). In this review, the major work about buried interface passivation for PSCs in recent years is summarized, expecting to provide a comprehensive review and a guidance for the research community.

Abstract

Owing to the merits of low cost and high power conversion efficiency (PCE), perovskite solar cells (PSCs) have become the best candidate to replace the commonly used silicon solar cells. However, PSCs have been slow to enter the market for a number of reasons, including poor stability, high toxicity, and rigorous preparation process. Passivation strategies including surface passivation and bulk passivation have been successfully applied to improve the device performance of PSCs. The passivation of the defects at the buried interface, which is regarded as a key strategy to breakthrough the device efficiency and stability of PSCs in the future, is ongoing with challenge. Herein, in detail the recent passivation of the buried interface is introduced from three aspects: perovskite layer, buried interlayer, and transport layer. The passivation effect of the buried interface is clearly demonstrated through three categories of salts, organics, and 2D materials. In addition, the transport layer is classified into electron transport layer (ETL) and hole transport layer (HTL). These classifications can help to have a clear understanding of substances which generate passivating effect and guide the continuous promotion of the follow-up buried interface passivating work.

This Study uses a non-continuous layer of alumina nanoparticles on the surface of rough Pb:Sn perovskite films, resulting in improved conformality of the subsequent electron transport layer. This leads to the alumina nanoparticle layer acting as an interfacial buffer layer between the rough absorber and top metal electrodes and hinders unwanted direct contact between them.

Abstract

Mixed lead-tin (Pb:Sn) halide perovskites are promising absorbers with narrow-bandgaps (1.25–1.4 eV) suitable for high-efficiency all-perovskite tandem solar cells. However, solution processing of optimally thick Pb:Sn perovskite films is notoriously difficult in comparison with their neat-Pb counterparts. This is partly due to the rapid crystallization of Sn-based perovskites, resulting in films that have a high degree of roughness. Rougher films are harder to coat conformally with subsequent layers using solution-based processing techniques leading to contact between the absorber and the top metal electrode in completed devices, resulting in a loss of V _OC, fill factor, efficiency, and stability. Herein, this study employs a non-continuous layer of alumina nanoparticles distributed on the surface of rough Pb:Sn perovskite films. Using this approach, the conformality of the subsequent electron-transport layer, which is only tens of nanometres in thickness is improved. The overall maximum-power-point-tracked efficiency improves by 65% and the steady-state V _OC improves by 28%. Application of the alumina nanoparticles as an interfacial buffer layer also results in highly reproducible Pb:Sn solar cell devices while simultaneously improving device stability at 65 °C under full spectrum simulated solar irradiance. Aged devices show a six-fold improvement in stability over pristine Pb:Sn devices, increasing their lifetime to 120 h.

The key role of methylammonium chloride additive in directing the crystallization of 1.8 eV perovskites to induce more effective halide homogenization is elucidated. The as-formed perovskite demonstrates suppressed halide segregation, improved optoelectronic properties, and ambient stability. In conjunction with a self-assembled monolayer (Me-4PACz), a V _OC of 1.25 V and steady-state PCE of 17% are achieved.

Abstract

Metal halide perovskite based tandem solar cells are promising to achieve power conversion efficiency beyond the theoretical limit of their single-junction counterparts. However, overcoming the significant open-circuit voltage deficit present in wide-bandgap perovskite solar cells remains a major hurdle for realizing efficient and stable perovskite tandem cells. Here, a holistic approach to overcoming challenges in 1.8 eV perovskite solar cells is reported by engineering the perovskite crystallization pathway by means of chloride additives. In conjunction with employing a self-assembled monolayer as the hole-transport layer, an open-circuit voltage of 1.25 V and a power conversion efficiency of 17.0% are achieved. The key role of methylammonium chloride addition is elucidated in facilitating the growth of a chloride-rich intermediate phase that directs crystallization of the desired cubic perovskite phase and induces more effective halide homogenization. The as-formed 1.8 eV perovskite demonstrates suppressed halide segregation and improved optoelectronic properties.

A highly efficient hole-transport-layer-free perovskite light-emitting diode with a record large external quantum efficiency of 16.7% is demonstrated through a multifunctional self-assembled molecule doping strategy, which not only lowers the hole injection barrier at the interface, but also suppresses the trap density and regulates the crystallization process for monodispersed phase composition in the quasi-2D perovskite films.

Abstract

Hole-transport-layer-free (HTL-free) perovskite light-emitting diodes (PeLEDs) are attracting increasing research attention because of their simplified device structure, fast preparation process, and high cost effectiveness. However, their much lower external quantum efficiency (EQE) as compared with the conventional p-i-n type ones has considerably limited their application prospects. Here, a self-assembled molecule (SAM) doping strategy is proposed by introducing [4-(3,6-dimethyl-9H-carbazol-9-yl) butyl] phosphonic acid (Me-4PACz) containing PO functional groups into the perovskite precursor solution and preparing the HTL-free quasi-2D perovskite films through the one-step spin-coating process. The doped Me-4PACz molecules can not only accumulate at the ITO/perovskite interface to lower the hole injection barrier, but also extend deep into the perovskite layer to suppress the trap density in perovskite films and regulate the crystallization process for monodispersed phase composition. With the further addition of ethoxylated trimethylolpropane triacrylate small molecule containing CO groups to passivate the defects synergistically with Me-4PACz, the EQE of the corresponding device is boosted from 1.5% to 16.7% together with a 3.5-fold increase in operational stability, which is the highest efficiency reported so far for HTL-free PeLEDs. The results demonstrate that the SAM doping strategy can be a viable and facile way to prepare high-performance HTL-free PeLEDs for practical applications.

Recent research progress on the strategies to fabricate phase-pure α-FAPbI₃ perovskite and the advances in their photovoltaic application is reviewed. The fundamental challenges of preparing efficient α-FAPbI₃ perovskite solar cells (PSCs) and some perspectives on the further development of high-quality phase-pure α-FAPbI₃ for reliable PSCs are discussed.

Formamidinium lead triiodide (FAPbI₃) with an optimal bandgap of 1.48 eV and superior thermal stability is regarded as one of the most promising perovskite-based materials for the application in efficient single-junction solar cells. However, the metastable properties of FAPbI₃ due to phase transition from photoactive α phase into an undesired nonperovskite δ phase in ambient conditions become the major factors limiting its further development. Challenges remain in stabilizing α phase structure and preparing phase-pure α-FAPbI₃ films for high-efficiency and stable perovskite solar cells (PSCs) devices. Herein, the recent research progress on the strategies is reviewed to fabricate phase-pure α-FAPbI₃ perovskite and the advances in their photovoltaic application. The physical parameters affecting the phase instability of intrinsic FAPbI₃ are first discussed, followed by various methodologies for regulating phase transition behavior, such as additive engineering, solvent optimization, dimensionality engineering, and fabrication techniques. Finally, the fundamental challenges of preparing efficient α-FAPbI₃ PSCs are discussed, and the perspectives on the further development of high-quality phase-pure α-FAPbI₃ for reliable PSCs are proposed.

Multi-functional phenylethylammonium trifluoroacetate performs three functions on perovskites: dimensionality control, defect passivation, and surface modification. Consequently, the optimized devices exhibit a remarkable external quantum efficiency of 11.87% at 468 nm, the highest reported to date for pure-blue perovskite light-emitting devices.

Abstract

Lead halide perovskites have shown exceptional performance in light-emitting devices (PeLEDs), particularly in producing significant electroluminescence in sky-blue to near-infrared wavelengths. However, PeLEDs emitting pure-blue light at 465–475 nm are still not satisfactory. Herein, efficient and stable pure-blue PeLEDs are reported by controlling phase distribution, passivation of defects, as well as surface modifications using multifunctional phenylethylammonium trifluoroacetate (PEATFA) in reduced-dimensional p-F-PEA₂Cs _n−1Pb _n (Br_0.55Cl_0.45)_3n+1 polycrystalline perovskite films. Compared with 4-fluorophenylethylammonium (p-F-PEA⁺) in the pristine films, phenylethylammonium (PEA⁺) has lower adsorption energy while interacting with perovskites, resulting in large-n low-dimensional perovskites, which can greatly facilitate charge transport within the low-dimensional perovskite films. The interaction between the CO group in trifluoroacetate (TFA⁻) and perovskites significantly reduces defects in the perovskite films. Additionally, the electron-giving CF₃ group in TFA- uplifts surface potential in the films, resulting in smooth electronic injection in devices. The multifunctional additive strategy leads to elevated radiative recombination and efficient carrier transport in the films and devices. As a result, the devices exhibit a maximum external quantum efficiency (EQE) of 11.87% at 468 nm with stable spectral output, the highest reported to date for pure-blue PeLEDs. Thus, this study extends the way for high-efficiency pure-blue LED with perovskite polycrystal films.