Chen Weijie

In this work, the effect of ionic liquid 1-hexyl-3-methylimidazolium iodide (HMII) on intragrain defects of formamidinium lead iodide (FAPbI₃) perovskite is investigated. Ultra-low dose electron diffraction patterns reveal that the addition of ionic liquid HMII significantly reduces the abundant {111}_c intragrain planar defects in FAPbI₃ grains.

Abstract

Ionic liquids have been widely used to improve the efficiency and stability of perovskite solar cells (PSCs), and are generally believed to passivate defects on the grain boundaries of perovskites. However, few studies have focused on the relevant effects of ionic liquids on intragrain defects in perovskites which have been shown to be critical for the performance of PSCs. In this work, the effect of ionic liquid 1-hexyl-3-methylimidazolium iodide (HMII) on intragrain defects of formamidinium lead iodide (FAPbI₃) perovskite is investigated. Abundant {111}_c intragrain planar defects in pure FAPbI₃ grains are found to be significantly reduced by the addition of the ionic liquid HMII, shown by using ultra-low-dose selected area electron diffraction. As a result, longer charge carrier lifetimes, higher photoluminescence quantum yield, better charge carrier transport properties, lower Urbach energy, and current–voltage hysteresis are achieved, and the champion power conversion efficiency of 24.09% is demonstrated. These observations suggest that ionic liquids significantly improve device performance resulting from the elimination of {111}_c intragrain planar defects.

In this work, 4,4′- (Hexafluoroisopropylidene) diphthalic anhydride (6FDA) is used as the additive in printable mesoscopic perovskite solar cells. This fluorinated molecule improves the perovskite crystallinity, passivates perovskite defects, and enhances long-term operation stability. Under these synergistic effects, the device has an average V _OC increase over 50 mV and the champion device has a PCE of 20.15%.

Abstract

Benefiting from their simple and cost-effective fabrication procedures, printable mesoscopic perovskite solar cells (p-MPSCs) exhibit substantial potential for large-scale production. In p-MPSCs, the thickness of the perovskite filled in the TiO₂ and ZrO₂ mesoporous layers is ≈3 µm. Therefore, the perovskite crystallization process is more intricate and challenging in the mesoporous structure than the general planar thin film (0.3–0.5 µm). In this work, a multifunctional fluorinated molecule is applied to work as an additive to improve the perovskite crystallization, enhance the device efficiency, and elevate the operational stability. This additive forms robust coordination between its carbonyl groups and uncoordinated Pb²⁺, thereby effectively passivating defects. The hydrophobic properties of the fluorinated molecule contribute to the device's water-resistant capability and long-term operational stability. With these synergistic effects, the power conversion efficiency (PCE) of small-area cells (0.1 cm²) reaches 20.15% under 1 sun illumination. Large-area modules (56.4 cm²) are fabricated and exhibit a PCE of 15.41%.

A host-guest design strategy is adopted to simultaneously improve the exciton radiative recombination and charge injection efficiency in lead-free [dppb]₂Cu₂I₂ emitters. Consequently, efficient green-emitting LEDs with a record external quantum efficiency of 13.39% and a large-area emitting area up to 81 cm² with uniform emission are realized, substantially surpassing those of recently reported Cu halide-based devices.

Abstract

Ternary copper (Cu) halides are promising candidates for replacing toxic lead halides in the field of perovskite light-emitting diodes (LEDs) toward practical applications. However, the electroluminescent performance of Cu halide-based LEDs remains a great challenge due to the presence of serious nonradiative recombination and inefficient charge transport in Cu halide emitters. Here, the rational design of host-guest [dppb]₂Cu₂I₂ (dppb denotes 1,2-bis[diphenylphosphino]benzene) emitters and its utility in fabricating efficient Cu halide-based green LEDs that show a high external quantum efficiency (EQE) of 13.39% are reported. The host-guest [dppb]₂Cu₂I₂ emitters with mCP (1,3-bis(N-carbazolyl)benzene) host demonstrate a significant improvement of carrier radiative recombination efficiency, with the photoluminescence quantum yield increased by nearly ten times, which is rooted in the efficient energy transfer and type-I energy level alignment between [dppb]₂Cu₂I₂ and mCP. Moreover, the charge-transporting mCP host can raise the carrier mobility of [dppb]₂Cu₂I₂ films, thereby enhancing the charge transport and recombination. More importantly, this strategy enables a large-area prototype LED with a record-breaking area up to 81 cm², along with a decent EQE of 10.02% and uniform luminance. It is believed these results represent an encouraging stepping stone to bring Cu halide-based LEDs from the laboratory toward commercial lighting and display panels.

A record efficiency of 25.64% is achieved for NiOx-based inverted perovskite solar cell via a surface reconstruction strategy utilized lead chelation (LC) molecules. The LC molecules target passivates the undesirable defects while avoids the adverse clustering in local areas on perovskite surface during the surface reconstruction process, thereby maximizing the passivation effect.

Abstract

Functional agents are verified to efficiently enhance device performance of perovskite solar cells (PSCs) through surface engineering. However, the influence of intrinsic characteristics of molecules on final device performance is overlooked. Here, a surface reconstruction strategy is developed to enhance the efficiency of inverted PSCs by mitigating the adverse effects of lead chelation (LC) molecules. Bathocuproine (BCP) is chosen as the representative of LC molecules for its easy accessibility and outstanding optoelectronic properties. During this strategy, BCP molecules on perovskite surface are first dissolved in solvents and then captured specially by undercoordinated Pb²⁺ ions, preventing adverse n-type doping by the molecules themselves. In this case, the BCP molecule exhibits outstanding passivation effect on perovskite surface, which leads to an obviously increased open-circuit voltage (V _OC). Therefore, a record power conversion efficiency of 25.64% for NiO _x -based inverted PSCs is achieved, maintaining over 80% of initial efficiency after exposure to ambient condition for ≈1500 h.

Publication date: 10 July 2024

Source: Electrochimica Acta, Volume 492

Author(s): Minghuang Guo, Yongsheng Chen, Shaolin Chen, Caixin Zuo, Yafeng Li, Yuan Jay Chang, Junming Li, Mingdeng Wei

A simple encapsulation process is demonstrated using a transparent electrode-integrated flexible barrier (TIFB) substrate. Having a 4.3 × 10⁻³ g m⁻² day of low water vapor transmission rate, the optimized TIFB/silicon nitride–polyethylene terephthalate can protect and preserve the initial perovskite film state and device performance for over 400 h.

Flexible perovskite solar cells (PSCs) have been rapidly developed for realistic applications such as windows and auxiliary power supplies of electronics. However, the moisture penetration through the flexible substrate films still poses a major obstacle because it can destroy the perovskite films under outdoor conditions. Unlike conventional PSCs with glass-based encapsulation, flexible PSCs face challenges in finding suitable materials and structures that maintain flexibility while providing effective encapsulation. Simple encapsulation methods for flexible PSCs are proposed using a transparent electrode-integrated flexible barrier (TIFB) substrate comprising silicon nitride (SiN _x )/polyethylene terephthalate (PET)/indium tin oxide (ITO). A dense SiN _x layer with chemical vapor deposition on ITO–PET films is deposited and a more flexible TIFB than the conventional laminated substrate owing to its thinness is achieved. TIFB shows a low water vapor transmission rate of 4.3 × 10⁻³ g m⁻² day. Consequently, the efficiency of TIFB-based PSCs under harsh conditions (60 °C and 90RH%) exhibits an acceptable decrease within 10% of its highest efficiency after 400 h, which is the most stable data under high temperature and humidity among existing flexible encapsulated PSCs. TIFB, as a flexible substrate, is a major candidate to protect flexible electronics and PSCs against external factors.

Herein, 1-methyl-2-pyrrolidone is used as a cosolvent to adjust the annealing-free preparation process of printable mesoscopic perovskite solar cells with 2-methoxyethanol as the solvent. The 1-methyl-2-pyrrolidone effectively slows down the crystallization process of the perovskite film. Finally, the highest power conversion efficiency of annealing-free printable mesoscopic perovskite solar cells is achieved.

The one-step drop-casting for preparing perovskite films in three-layer mesoporous for printable mesoscopic perovskite solar cells always results in insufficient filling of mesopores. A binary solvent based on 2-methoxyethanol (2-ME) and 1-methyl-2-pyrrolidone (NMP) offers a method suitable for annealing-free to prepare dense perovskite films in mesopores. The crystallization process of perovskite films in mesopores can be adjusted by the content of NMP in the solvent. The introduction of NMP enhances the density of the perovskite film based on the binary solvent system, optimizing the contact between the perovskite film and the mesoporous scaffold. When the ratio of 2-ME to NMP is 9:1, the optimal device achieves impressive performance metrics, including a power conversion efficiency (PCE) of 17.28%, an open-circuit voltage of 0.98 V, a short-circuit current of 23.80 mA cm⁻², and a fill factor of 74.08%. This represents the highest PCE achieved to date in the annealing-free preparation of perovskite films for printable mesoscopic perovskite solar cells. Furthermore, devices based on this binary solvent system exhibit remarkable stability, with almost no loss in efficiency even after 120 days of storage in an air environment without encapsulation.

This work presents an analytical model for describing the bias-assisted charge extraction transient photocurrent for organic solar cells with low carrier mobility and predominant bimolecular recombination during charge extraction. Upon fitting to the extracted photocurrent curve, this model provides valuable insights for accurately determining carrier density and mobilities in operating devices.

Bias-assisted charge extraction (BACE) is a powerful technique for measuring the carrier density in organic solar cells under operational conditions and to deduce information on the charge recombination properties. Hereby, the carrier density in the active layer device is determined by integrating the transient extraction current, while nongeminate recombination during the charge extraction processes is generally neglected. This assumption becomes questionable for low mobilities, for example, at low temperatures and in case of high energetic disorder. Herein, the extraction process in BACE measurement is investigated by incorporating both drift and bimolecular recombination of charges during charge extraction into a unified framework. An explicit analytical model is proposed to describe the time dependence of the transient photocurrent in BACE measurement and excellent agreement is found with drift-diffusion simulations. It is shown that global fitting of transient photocurrents measured at various collection biases with this analytical model allows to determine the carrier density in the device with high accuracy. Furthermore, the analytical model is demonstrated to provide accurate mobilities for both the fast and slow carriers within the device, rendering it a valuable supplement to other mobility measurement techniques such as resistance-dependent photovoltage and space–charge-limited current.

The covalent bonds between the FA cations and the HNCO additives give rise to an efficient passivation on the perovskite films, resulting in an improved film quality, a suppressed non-radiation recombination, a facilitated carrier transport, and a better energy band levels alignment. Consequently, the modified devices show excellent power conversion efficiency and stability.

Abstract

Organometal halide perovskite solar cells (PSCs) have received great attention owing to a rapid increase in power conversion efficiency (PCE) over the last decade. However, the deficit of long-term stability is a major obstacle to the implementation of PSCs in commercialization. The defects in perovskite films are considered as one of the primary causes. To address this issue, isocyanic acid (HNCO) is introduced as an additive into the perovskite film, in which the added molecules form covalent bonds with FA cations via a chemical reaction. This chemical reaction gives rise to an efficient passivation on the perovskite film, resulting in an improved film quality, a suppressed non-radiation recombination, a facilitated carrier transport, and optimization of energy band levels. As a result, the HNCO-based PSCs achieve a high PCE of 24.41% with excellent storage stability both in an inert atmosphere and in air. Different from conventional passivation methods based on coordination effects, this work presents an alternative chemical reaction for defect passivation, which opens an avenue toward defect-mitigated PSCs showing enhanced performance and stability.

The surface passivators strategy is designed that combine the electron-donating methoxy group and π–π conjugation of the phenyl ring to reduce the local potential at the reactive site of formamidinium group. This strategy effectively suppresses the surface nonradiative recombination and promotes the interface carrier extraction without the formation of a low-dimension phase. The modified devices achieve a peak PCE of 25.88%.

Abstract

The conjugation of terminal ammonium salt groups with perovskite surfaces is a frequently employed technique that aims to enhance the overall performance of perovskite materials, encompassing both bulk and surface properties. Particularly, it exhibits heightened efficacy when applied to surface modification, due to its ability to mitigate defect accumulation and facilitate facile binding with the receptive sites inherent to the perovskite structure. However, the interaction of the bulk ammonium group with PbI₂ has the potential to form a low-dimensional phase of perovskite, which may obstruct carrier extraction at the interface. Therefore, the surface passivators (MeO-PFACl) are designed through intramolecular potential manipulation. The combinations of the electron-donating methoxy group and π–π conjugation of the phenyl ring reduce the local potential at the reactive site of formamidinium group, making it less likely to form a low-dimension phase with perovskite. This surface passivation strategy effectively suppresses the surface nonradiative recombination and promotes the interface carrier extraction. The devices treated with MeO-PFACl have demonstrated exceptional performance, achieving a peak power conversion efficiency (PCE) of 25.88%, with an average PCE of 25.37%. These works offer a novel principle for enhancing both the efficiency and stability of PSCs using ammonium-incorporated molecules without the induction of an additional phase layer.

A 2D alkalis-intercalated-vermiculite is developed as buried atomical lubricant and ionic soil to universally eliminate the downward-growth-induced lattice disorders in perovskite film. Owing to the tensile strain release and the formation of ion-diffusion-induced bottom-up passivation gradient, the efficiency and long-term stability of perovskite solar cells is significantly improved.

Abstract

Mixed-halide perovskites are emerging as excellent photovoltaic candidates because of their tunable bandgaps for semitransparent and tandem perovskite solar cells. However, the notorious film quality originated from the rapidly downward crystallization process susceptibly propagates enormous detrimental defects, which deteriorate the photovoltaic performance and accelerate halide segregation. To address this issue, herein, a multilayer alkalis-intercalated-vermiculite is employed as pre-buried interface modifier to regulate the perovskite lattice property. The matchable lattice structure between perovskite and vermiculite by forming Pb─O bond not only releases the interfacial strain during the film growth but also the embedded alkalis ions can gradually diffuse into perovskite lattice to form a favorable vertical gradient owing to the weak interlamellar van der Waals interaction, playing bis-roles of atomical lubricant and ion-reservoir to eliminate detrimental defects. As a result, the film quality and lattice stability is significantly improved with suppressed phase segregation for mixed-halide perovskites, accompanying a champion efficiency of 11.42% for carbon-based CsPbIBr₂ device, 15.25% for carbon-based CsPbI₂Br device and 23.17% for p-i-n inverted (Cs_0.05MA_0.05FA_0.9)Pb(I_0.93Br_0.07)₃ cell. This work provides a new strategy on buried interface engineering for making high-efficiency and stable perovskite platforms.

An efficient additive (6BAS) with multisite anchoring (C═O) as can promote the preferential crystallization of perovskite for realizing high-quality perovskite films with larger grain size and reduced defect state, which is beneficial to hot carriers extraction from perovskite layer into carrier transport layers and the decreased charge recombination rate in 6BAS-modified device. Consequently, highly efficient PSCs are achieved.

Abstract

Modulating perovskite crystallization and understanding hot carriers (HCs) dynamics in perovskite films are very critical to achieving high-performance perovskite solar cells (PSCs). Herein, a small organic molecule (6BAS) with multisite anchors (C═O) as an efficient additive is introduced into PbI₂ precursors to modulate perovskite crystallization during two-step sequential deposition. The chemical interaction between 6BAS and PbI₂ enables more preferential PbI₂ crystal with enlarged interplanar spacing of PbI₂ lattice, which is beneficial to the penetration of organic ammonium salts into PbI₂ layer and the complete conversion to perovskite, consequently promoting the preferential crystallization of perovskite to realize high-quality perovskite films with larger grain size and reduced defect state. By ultrafast spectroscopy, it is found that the incorporation of 6BAS can efficiently prolong HCs cooling, which helps to enhance HCs transfer and retard the charge carrier recombination in device. As a result, 6BAS doped-PSCs efficiency significantly enhances to 25.32% from 22.91%. The target device achieves the enhanced long-term stability. Only a 6% efficiency degradation is realized for un-encapsulated device with 6BAS after 70 days under N₂. Meanwhile, the 6BAS-treated device retains 95% of its initial PCE after 1160 h of operation at the maximum power point under continuous AM 1.5 G illumination.

Herein, a quantitative deposition method is developed through drop-on-demand inkjet printing to study the influence of 2-adamantylamine hydrochloride (2-ADAHCl) deposition surface density on the device performance. Through quantitative passivator deposition, the passivation capability and interfacial contact between perovskite and hole transport layer are balanced. As a result, the power conversion efficiency and stability are significantly improved.

Abstract

Deposition of a passivation layer on top of the perovskite is proven to be an effective method for improving the efficiency and long-term stability of perovskite solar cells (PSCs). And the spin-coating method is the most typical and popular method developed for this purpose. However, the spin-coating method wastes substantial passivator materials, thus the quantitative relationship between the passivator amount and the device performance cannot be obtained. Herein, a quantitative deposition method is developed through drop-on-demand inkjet printing to investigate the influence of 2-adamantylamine hydrochloride (2-ADAHCl) deposition surface density on the device performance, which is found to have a significant impact on the device performance. A low deposition surface density of 1.1 µg cm⁻² does not reach its optimum passivation capability. In contrast, an excess deposition surface density of 10.1 µg cm⁻² would lead to energy level mismatch and large series resistance at the perovskite/hole transport layer (HTL) interface, thus resulting in inferior device properties. At an optimum deposition surface density of 2.5 µg cm⁻², perovskite surface defects are greatly suppressed, and the interfacial contact between perovskite and HTL is improved. Finally, PSCs with a high efficiency of 24.57% are achieved with improved operational and environmental stabilities.

New lead-free 2D Dion–Jacobson tin perovskites containing the 4-(aminomethyl)piperidinium (4AMP) spacer cation are studied: (4AMP)SnI₄, (4AMP)(MA)Sn₂I₇, and (4AMP)(FA)Sn₂I₇ (MA = methylammonium, FA = formamidinium). Structural analysis reveals that only (4AMP)SnI₄ is noncentrosymmetric, confirmed by second harmonic generation. Ferroelectric hysteresis measurements provide clear evidence of ferroelectricity of (4AMP)SnI₄ at room temperature with spontaneous polarization of 10.0 µC cm⁻².

Abstract

2D hybrid organic–inorganic halide perovskites emerge as a new class of 2D semiconductors with the potential to combine excellent optoelectronic properties with symmetry-enabled properties such as ferroelectricity. Although many lead-based ferroelectric 2D halide perovskites are reported, there is yet to be a conclusive report of ferroelectricity in tin-based 2D perovskites. Here, the structures and properties of a new series of 2D Dion–Jacobson (DJ) Sn perovskites: (4AMP)SnI₄, (4AMP)(MA)Sn₂I₇, and (4AMP)(FA)Sn₂I₇ (4AMP = 4-(aminomethyl)piperidinium, MA = methylammonium, and FA = formamidinium), are reported. Structural characterization reveals that (4AMP)SnI₄ is polar with in-plane spontaneous polarization whereas (4AMP)(MA)Sn₂I₇ and (4AMP)(FA)Sn₂I₇ are centrosymmetric. Further, (4AMP)SnI₄ displays second harmonic generation (SHG) and polarization-electric field hysteresis measurements confirm it is ferroelectric with a spontaneous polarization of 10.0 µC cm⁻² at room temperature. (4AMP)SnI₄ transitions into a centrosymmetric structure above 367 K. As the first direct experimental observation of the spontaneous ferroelectric polarization of a Sn-based 2D hybrid perovskite, this work opens up environmentally friendly 2D tin halide perovskites for ferroelectricity and other physical property studies.

A novel hole-transporting material [4-(3,6-glycol monomethyl ether-9H-carbazol-9-yl) butyl]phosphonic acid (GM-4PACz) is synthesized by introducing glycol monomethyl ether (GM) at carbazolyl unit, which facilitates the spreading of perovskite, has well matching energy band with perovskite, suppresses defects and releases residual stress at buried interface of inverted perovskite solar cells (IPSCs). Consequently, GM-4PACz-based IPSCs engender a high efficiency of 25.52 % and an excellent operational stability.

Abstract

Organic self-assembled molecules (OSAMs) based hole-transporting materials play a pivotal role in achieving highly efficient and stable inverted perovskite solar cells (IPSCs). However, the reported carbazol-based OSAMs have serious drawbacks, such as poor wettability for perovskite solution spreading due to the nonpolar surface, worse matched energy arrangement with perovskite, and limited molecular species, which greatly limit the device performance. To address above problems, a novel OSAM [4-(3,6-glycol monomethyl ether-9H-carbazol-9-yl) butyl]phosphonic acid (GM-4PACz) was synthesized as hole-transporting material by introducing glycol monomethyl ether (GM) side chains at carbazolyl unit. GM groups enhance the surface energy of Indium Tin Oxide (ITO)/SAM substrate to facilitate the nucleation and growth of up perovskite film, suppress cation defects, release the residual stress at SAM/perovskite interface, and evaluate energy level for matching with perovskite. Consequently, the GM-4PACz based IPSC achieves a champion PCE of 25.52 %, a respectable open-circuit voltage (V _OC) of 1.21 V, a high stability, possessing 93.29 % and 91.75 % of their initial efficiency after aging in air for 2000 h or tracking at maximum power point for 1000 h, respectively.

The phase stability and photoelectric properties of CsPbI₂Br films are significantly improved by a dual-doping strategy with CaCl₂ and InCl₃ additives. Thus, the unencapsulated dual-doping perovskite solar cell with the power conversion efficiency (PCE) of 15.51% remains 90% of the original PCE after aging 2400 h under ambient air and 1500 h under continuous illumination.

It is fundamentally challenging to achieve stable and efficient all-inorganic perovskite solar cells (PSCs) in ambient air conditions for low-cost commercial manufacturing, as the crystallinity, surface morphology, and optical activity of all-inorganic perovskites exhibit high sensitivity to environmental factors such as moisture and illumination. Herein, a dual-doping strategy is presented to prepare high-quality dual-doping CsPbI₂Br films under ambient air with relative humidity of 70% (70% RH) by introducing CaCl₂ and InCl₃ additives into precursor solution. The results from the experiments and calculations reveal that the CaCl₂ additive can isolate moisture by forming hydrates at the surface and grain boundary of perovskites. Meanwhile, the addition of InCl₃ can significantly improve the optoelectronic properties via the heterovalent substitution of Pb²⁺ by a small amount of In³⁺. Moreover, the phase segregation can be significantly suppressed in the dual-doping CsPbI₂Br films owing to decreasing the electron–phonon coupling strength and increasing the activation energy of ion migration. The unencapsulated dual-doping CsPbI₂Br PSC with the power conversion efficiency (PCE) of 15.51% (70% RH) demonstrates high humidity storage and long-term optical stability, remaining 90% of the original PCE after aging 2400 h under ambient air (50% RH) and 1500 h under continuous illumination, respectively.

Nature Materials, Published online: 29 April 2024; doi:10.1038/s41563-024-01876-2

Publication date: July 2024

Source: Nano Energy, Volume 126

Author(s): Ran Li, Mina Guli, Wenkai He, Cheng Lan, Yancheng Zhou, Yujing Zhang

Large-area SnO₂ electron transporting layers have been fabricated by a combination of atomic layer deposition and chemical bath deposition. The bilayer structure not only enhances the coverage but also optimizes the morphology of the perovskite at the buried surface. An efficiency of 17.9% for perovskite solar modules with an active area of 48 cm² is achieved.

Tin oxide (SnO₂) is one of the most promising electron transport layers (ETL) for the commercialization of perovskite solar cells (PSCs) due to its excellent electron mobility and high transparency, along with its low processing temperature. However, the inherent defects, nonuniform coating, and poor surface morphology of SnO₂ may be detrimental to the physicochemical properties, such as conductivity and electron mobility at the interface, lead to a decrease in the open-circuit voltage (V _OC) and a reduction in device stability. In this study, a method that combines atomic layer deposition and chemical bath deposition techniques to solve these issues is presented. The presence of bilayer ETLs enhances the coverage of the SnO₂ film and optimizes the morphology of the buried surface of perovskite, which not only facilitates the interfacial charge transfer but also suppresses recombination reactions. As a result, a significant increase in V _OC and efficiency has been achieved compared to devices with only a single layer. Additionally, the large-area perovskite solar module (active area: 48.0 cm²) achieves a champion efficiency of 17.9%. The PSCs retain more than 93% of their initial efficiency after 700 h of continuous operation under 1-sun illumination and 25 °C.

Treating the mesoscopic TiO₂ electron transport layer with guanidine sulfate facilitates a dual passivation by inducing in situ reactions that suppresses non-radiative recombination and promotes charge extraction in printable hole-conductor-free mesoscopic perovskite solar cells with carbon electrodes. The treatment ultimately diminishes the open-circuit voltage loss and improves the power conversion efficiency from 17.51% to 18.70%.

Abstract

Numerous defects exist at the buried interface between the perovskite and adjacent electron transport layers in perovskite solar cells, resulting in severe non-radiative recombination and excessive open-circuit voltage (V _OC) loss. Herein, a dual defect passivation strategy utilizing guanidine sulfate (GUA₂SO₄) as an interface modifier is first reported. On the one hand, the SO₄ ²⁻ preferentially interacts with Pb-related defects, generating water-insoluble lead oxysalts complexes. Additionally, GUA⁺ diffuses into the perovskite and induces the formation of low-dimensional perovskite. These reactions effectively suppress trap states at the buried interface and perovskite boundaries in printable mesoscopic perovskite solar cells (p-MPSCs), thus increasing the carrier lifetime. Meanwhile, GUA₂SO₄ optimizes the interface energy band alignment, thus accelerating the charge extraction and transfer at the buried interface. This synergistic effect of trap passivation and interface energy band alignment modulation is strongly demonstrated by an increase in average V _OC of 70 mV and the power conversion efficiency improvement from 17.51% to 18.70%. This work provides a novel approach to efficiently improve the performance of p-MPSCs through dual-targeted defect passivation at the buried interface.

A spontaneous compositional–interfacial co-modification strategy is developed to provide multifunctional protections for stable perovskite films by forming gradient structures through ion exchange reactions. As a result, the unencapsulated devices maintain 94%, 81%, and 83% of initial efficiency after aging in N₂, ambient air, and at 85 °C for 14016, 2500, and 1248 h, respectively, among the state-of-the-art stability of inverted perovskite solar cells.

Abstract

The long-term stability of perovskite solar cells (PSCs) is still challenging for commercialization and mainly linked to the life span of perovskite films. Herein, a spontaneous compositional–interfacial co-modification strategy is developed based on the ion exchange reaction by introducing ammonium hexafluorophosphate (NH₄PF₆) into antisolvent to form gradient structures through a simple one-step solvent engineering. With the assistance of the ion exchange reaction, NH₄PF₆ forms a multifunctional structure to protect perovskite films from both internal and external factors for the exceptionally long-term stability of photovoltaics. The reason for this is linked to the high hydrophobicity of NH₄PF₆ for preventing H₂O invasion, suppressing ion migration by forming hydrogen bonding, and reducing perovskite defects. The resulting unencapsulated devices show exceptionally long-term stability under standardized the International Summit on Organic Photovoltaic Stability (ISOS) protocols, with over 94%, 81%, and 83% retained power conversion efficiencies after aging tests under N₂ (ISOS-D-1I), ambient air (ISOS-D-1), and 85 °C (ISOS-D-2I) for 14016, 2500, and 1248 h, respectively. These performances compare well with the state-of-the-art stability of inverted PSCs. Further investigations are conducted to study the evolution of macroscopic morphology and microscopic crystal structure in aged perovskite films, aiming to provide evidence supporting the aforementioned improvements in stability.

2D perovskite passivation is a mainstream strategy to address the perovskite/C₆₀ interface problem. Organic molecules in 2D perovskites come into direct contact with C₆₀, forming π–π stacking at the perovskite/C₆₀ interface to enhance interaction. This improves the quality of the perovskite/C₆₀ interface and ultimately achieves the goal of enhancing device performance.

Abstract

Interface passivation is a key method for improving the efficiency of perovskite solar cells, and 2D/3D perovskite heterojunction is the mainstream passivation strategy. However, the passivation layer also produces a new interface between 2D perovskite and fullerene (C₆₀), and the properties of this interface have received little attention before. Here, the underlying properties of the 2D perovskite/C₆₀ interface by taking the 2D TEA₂PbX₄ (TEA = C₆H₁₀NS; X = I, Br, Cl) passivator as an example are systematically expounded. It is found that the 2D perovskite preferentially exhibits (002) orientation with the outermost surface featuring an oriented arrangement of TEACl, where the thiophene groups face outward. The outward thiophene groups further form a strong π–π stacking system with C₆₀ molecule, strengthening the interaction force with C₆₀ and facilitating the creation of a superior interface. Based on the vacuum-assisted blade coating, wide-bandgap (WBG, 1.77 eV) perovskite solar cells achieved impressive records of 19.28% (0.09 cm²) and 18.08% (1.0 cm²) inefficiency, respectively. This research not only provides a new understanding of interface processing for future perovskite solar cells but also lays a solid foundation for realizing efficient large-area devices.

The synergy of fluorination on the selenide monomer enables a novel polymer acceptor (PYSe2F-T) with a bathochromic absorption onset (≈1000 nm) and ordered packing. PYSe2F-T-based devices yield an impressive short-circuit current density of 27.7 mA cm⁻² with a higher efficiency of 16.7%. Beneficial from its near-infrared response, PYSe2F-T can also provide a decent performance of 12.6% in semitransparent devices with an average visible transmittance of 26.2%.

Abstract

All-polymer solar cells (all-PSCs) offer promising potential for large-scale manufacturing due to their remarkable mechanical and thermal stability. However, the limited capacity of polymer acceptors for near-infrared (NIR) photon harvesting has impeded their progress in semi-transparent (ST) all-PSCs. Here, the study develops a pair of new NIR polymer acceptors, named PYSeF-T and PYSe2F-T, with mono-/di-fluorinated end groups capped to the selenide monomer backbone, respectively. Owing to the stronger intermolecular interaction and intramolecular charge transfer effect of the di-fluorinated end groups with the selenide backbone, PYSe2F-T exhibits a stronger crystallinity and a more bathochromic absorption to 1000 nm. When blended with the donor, PM6, the PY2SeF-T-based all-PSC demonstrates a higher efficiency of 16.73% with a remarkable short-circuit current (J _SC) of 27.7 mA cm⁻², which is the highest J _SC for all-PSCs. Based on these, the ST device based on PM6:PYSe2F-T demonstrates a superior efficiency of 12.52% with an average visible transmittance of 26.2% and a light utilization efficiency of 3.28%, outperforming the mono-fluorinated counterpart. The work provides an in-depth understanding of the above synergistic effects to develop NIR polymer acceptors and establishes a solid foundation for future investigations into large-area and flexible ST all-PSCs.

A pseudoplanar heterojunction (PPHJ) structure with favorable verticalstratification is devised via printing method. The pre-deposited D18-Cl regulatesmolecular stacking and crystallization, further forming efficient carriertransport-collection channels and mitigating energy loss. Therefore, the optimized PPHJ devices perform excellent PCEs of 19.05% (100 nm), 17.33% (300 nm), 14.14% (4 cm²), showing great potential in production of stablelarge-area OSCs.

Abstract

Obtaining a well-accurate vertical distribution active layer morphology through the air-printing process is an essential task for achieving efficient scalable large-area organic solar cells (OSCs). In this target, the desired and controllable pseudo planar heterojunction (PPHJ) active layer structure with suitable phase separation is developed by pre-deposited D18-Cl layer under the PM6:BTP-eC9 film via an eco-friendly manufacturing method. The addition of the D18-Cl regulates molecular crystallization and leads to an ideal vertical stratification while simultaneously suppressing voltage loss, optimizing energetic disorder, and carrier management. Impressively, the optimal PPHJ devices perform superior power conversion efficiencies (PCEs) of 19.05% (100 nm), 17.33% (300 nm), and 14.14% (4 cm²) compared to the BHJ devices. Importantly, the PPHJ OSCs also exhibit an impressive extrapolated T₈₀ (the time required to reach 80% of initial PCE) of long-time storage and operational stability, as well as thermal stability.

A systematic study of the representative organic photovoltaic systems shows that the aggregation competition between polymer donor (PD) and non-fullerene acceptor (NFA) is a decisive factor in the phase separation of blend film and thus the photovoltaic performance. Based on 64 PD/NFA combinations, the aggregation ability/photovoltaic parameter heatmaps are plotted, providing a new matching rule for developing high-efficiency PD/NFA systems.

Abstract

In organic photovoltaic cells, the solution-aggregation effect (SAE) is long considered a critical factor in achieving high power-conversion efficiencies for polymer donor (PD)/non-fullerene acceptor (NFA) blend systems. However, the underlying mechanism has yet to be fully understood. Herein, based on an extensive study of blends consisting of the representative 2D-benzodithiophene-based PDs and acceptor–donor–acceptor-type NFAs, it is demonstrated that SAE shows a strong correlation with the aggregation kinetics during solidification, and the aggregation competition between PD and NFA determines the phase separation of blend film and thus the photovoltaic performance. PDs with strong SAEs enable earlier aggregation evolutions than NFAs, resulting in well-known polymer-templated fibrillar network structures and superior PCEs. With the weakening of PDs’ aggregation effects, NFAs, showing stronger tendencies to aggregate, tend to form oversized domains, leading to significantly reduced external quantum efficiencies and fill factors. These trends reveal the importance of matching SAE between PD and NFA. The aggregation abilities of various materials are further evaluated and the aggregation ability/photovoltaic parameter diagrams of 64 PD/NFA combinations are provided. This work proposes a guiding criteria and facile approach to match efficient PD/NFA systems.

Two-dimensional perovskite solar cells have remarkable promise as robust and efficient solar cells. The hole transport layer (HTL) plays a role in charge carriers transport and interface effects in two-dimensional perovskite devices. Based on the structural characteristics of two-dimensional perovskite solar cells, the importance of the HTL in crystalline control, phase distribution, and interface-passivation of two-dimensional perovskite is overviewed.

Although currently in the nascent stages of research and development, two-dimensional perovskite solar cells have showcased remarkable promise as the robust and efficient solar cell technology. Anticipated progressions and refinements in this domain are poised to establish two-dimensional perovskite cells as instrumental catalysts in shaping the trajectory of renewable energy, heralding transformative breakthroughs. The hole transport layer (HTL) plays an irreplaceable role in the charge carriers’ transport and interface effects in two-dimensional perovskite devices. This review starts with the structural characteristics of two-dimensional perovskite solar cells. The influence of the intrinsic characteristics of the perovskite active layer itself and the interaction of the perovskite/transport layer contact interface are analyzed. This discussion delves into the impact of intrinsic quantum confinement and the dielectric effect within the two-dimensional perovskite structure on photovoltaic conversion efficiency. It also explores the energy level alignment between the clathrate active layer and the transport layer. The significance of the HTL is emphasized, particularly regarding crystalline control, phase distribution, and interface passivation. Additionally, the crucial role of efficient carrier transport between the active layer and the transport layer is thoroughly examined.

Nature Energy, Published online: 26 April 2024; doi:10.1038/s41560-024-01504-y