Enhanced Device Stability Research Articles

Chiral cation promoted interfacial charge extraction for efficient tin-based perovskite solar cells

Pb-free Sn-based perovskite solar cells (PSCs) have recently made inspiring progress, and power conversion efficiency (PCE) of 14.8% has been achieved. However, due to the energy-level mismatch and poor interfacial contact between commonly used hole transport layer (i.e., poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate), PEDOT:PSS) and FASnI3 film, it is still challenging to effectively extract holes at the interface. Owing to the p-type nature of Sn-based perovskites, the efficient hole extraction is of particular significance to improve the PCE of their solar cells. In this work, for the first time, the role of chiral cations, α-methylbenzylamine (S-/R-/rac-MBA), in promoting hole transportation of FASnI3-based PSCs is demonstrated. The introduction of MBAs is found to form 2D/3D film with low-dimensional structures locating at PEDOT:PSS/FASnI3 interface, which facilitates the energy level alignment and efficient charge transfer at the interface. Importantly, chiral-induced spin selectivity (CISS) effect of R-MBA2SnI4 induced by chiral R-MBA cation is found to further assist the specific interfacial transport of accumulated holes. As a result, R-MBA-based PSCs achieve decent PCE of 10.73% with much suppressed hysteresis and enhanced device stability. This work opens up a new strategy to efficiently promote the interfacial extraction of accumulated charges in working PSCs.

Correlating the Active Layer Structure and Composition with the Device Performance and Lifetime of Amino-Acid-Modified Perovskite Solar Cells.

Additive engineering is emerging as a powerful strategy to further enhance the performance of perovskite solar cells (PSCs), with the incorporation of bulky cations and amino acid (AA) derivatives being shown as a promising strategy for enhanced device stability. However, the incorporation of such additives typically results in photocurrent losses owing to their saturated carbon backbones, hindering charge transport and collection. Here, we investigate the use of AAs with varying carbon chain lengths as zwitterionic additives to enhance the PSC device stability, in air and nitrogen, under illumination. We, however, discovered that the device stability is insensitive to the chain length as the anticipated photocurrent drops as the chain length increases. Using glycine as an additive results in an improvement in the open circuit voltage from 1.10 to 1.14 V and a resulting power conversion efficiency of 20.2% (20.1% stabilized). Using time-of-flight secondary ion mass spectrometry, we confirm that the AAs reside at the surfaces and interfaces of our perovskite films and propose the mechanisms by which stability is enhanced. We highlight this with glycine as an additive, whereby an 8-fold increase in the device lifetime in ambient air at 1 sun illumination is recorded. Short-circuit photoluminescence quenching of complete devices is reported, which reveals that the loss in photocurrent density observed with longer carbon chain AAs results from the inefficient charge extraction from the perovskite absorber layer. These combined results demonstrate new fundamental understandings about the photophysical processes of additive engineering using AAs and provide a significant step forward in improving the stability of high-performance PSCs.

Branched Methoxydiphenylamine-Substituted Carbazole Derivatives for Efficient Perovskite Solar Cells: Bigger Is Not Always Better.

A set of novel branched molecules bearing a different number of 3,6-bis(4,4′-dimethoxydiphenylamino)carbazole-based (Cz-OMeDPA) periphery arms linked together by aliphatic chains have been developed, and their performance has been tested in perovskite solar cells (PSCs). Electrical and photovoltaic properties have been evaluated with respect to the number of Cz-OMeDPA moieties and the nature of the linking aliphatic chain. The isolated compounds possess sufficient thermal stability and are amorphous having high glass-transition temperatures (>120 °C) minimizing the risk of direct layer crystallization. The highest hole-drift mobility of μ0 = 3.1 × 10–5 cm2 V–1 s–1 is comparable to that of the reference standard spiro-OMeTAD (4.1 × 10–5 cm2 V–1 s–1) under identical conditions. Finally, PSCs employing two new HTMs (2Cz-OMeDPA and 3Cz-OMeDPA-OH) bearing two and three substituted carbazole chromophores, linked by an aliphatic chain, show a performance of around 20%, which is on par with devices using spiro-OMeTAD and demonstrates slightly enhanced device stability.

Obstructing interfacial reaction between NiOx and perovskite to enable efficient and stable inverted perovskite solar cells

In NiOx-based perovskite solar cells (PVSCs), the interfacial redox reaction between Ni3+ (on the surface of NiOx) and A-site cation salt (MAI in perovskite precursor solution) is invariably ignored. This adverse reaction will generate PbI2-rich hole extraction barriers at the NiOx-perovskite interface, which limits hole transmission and increases charge recombination, thus resulting in open-circuit voltage (Voc) loss. Furthermore, it will accelerate perovskite degradation by deprotonating the precursor amine and oxidizing iodide to interstitial iodine, which induces the severe instability of devices. Herein, a physical separation strategy by introducing a modifier layer to obstruct the detrimental reaction is explored. The results demonstrate that the trimethylolpropane tris(2-methyl-1-aziridinepropionate) (SaC-100) depositing onto NiOx can suppress the reaction between Ni3+ and MAI to endow the improvement of conductivity and reduction of interfacial defects, thus reducing Voc loss and enhancing device stability. Moreover, the interfacial energy level alignment and the morphology of perovskite are also optimized. As a result, the PVSCs device based on NiOx/SaC-100 presents the best power conversion efficiency (PCE) of 20.21% with a superior Voc value of 1.12 V. Furthermore, the device shows better light and thermal stability because of the hindering effect and defect passivation effect of SaC-100.

Robust Molecular Dipole‐Enabled Defect Passivation and Control of Energy‐Level Alignment for High‐Efficiency Perovskite Solar Cells

AbstractThe ability to passivate defects and modulate the interface energy‐level alignment (IEA) is key to boost the performance of perovskite solar cells (PSCs). Herein, we report a robust route that simultaneously allows defect passivation and reduced energy difference between perovskite and hole transport layer (HTL) via the judicious placement of polar chlorine‐terminated silane molecules at the interface. Density functional theory (DFT) points to effective passivation of the halide vacancies on perovskite surface by the silane chlorine atoms. An integrated experimental and DFT study demonstrates that the dipole layer formed by the silane molecules decreases the perovskite work function, imparting an Ohmic character to the perovskite/HTL contact. The corresponding PSCs manifest a nearly 20 % increase in power conversion efficiency over pristine devices and a markedly enhanced device stability. As such, the use of polar molecules to passivate defects and tailor the IEA in PSCs presents a promising platform to advance the performance of PSCs.

Robust Molecular Dipole-Enabled Defect Passivation and Control of Energy-Level Alignment for High-Efficiency Perovskite Solar Cells.

The ability to passivate defects and modulate the interface energy-level alignment (IEA) is key to boost the performance of perovskite solar cells (PSCs). Herein, we report a robust route that simultaneously allows defect passivation and reduced energy difference between perovskite and hole transport layer (HTL) via the judicious placement of polar chlorine-terminated silane molecules at the interface. Density functional theory (DFT) points to effective passivation of the halide vacancies on perovskite surface by the silane chlorine atoms. An integrated experimental and DFT study demonstrates that the dipole layer formed by the silane molecules decreases the perovskite work function, imparting an Ohmic character to the perovskite/HTL contact. The corresponding PSCs manifest a nearly 20 % increase in power conversion efficiency over pristine devices and a markedly enhanced device stability. As such, the use of polar molecules to passivate defects and tailor the IEA in PSCs presents a promising platform to advance the performance of PSCs.

An Effective Strategy of Combining Surface Passivation and Secondary Grain Growth for Highly Efficient and Stable Perovskite Solar Cells.

Interfacial engineering methods have been developed to solve defect issues of perovskite solar cells (PSCs). However, traditional surface passivation has limited effects on eliminating defect-forming residuals, while secondary grain growth (SGG) is restricted by limited choices of additives and intrinsic properties of perovskites. Here, a pincer strategy of taking advantages of surface passivation and SGG is proposed to modify both exterior and interior of CH3 NH3 PbI3 (MAPbI3 ) perovskite, by employing cyanoacetate-containing donor-acceptor compounds (CA-D-A) including 2-cyano-3-(3,4,5-trimethoxyphenyl)acrylic acid (CA), methanaminium 2-cyano-3-(3,4,5-trimethoxyphenyl)acrylate (CAMA), and aminomethaniminium (Z)-2-cyano-3-(3,4,5-trimethoxyphenyl)acrylate (CAFA). In comparison to untreated perovskite, CA-D-A treated perovskites present better crystallinity because of SGG, lower trap densities due to the synergistic effect of surface passivation and SGG, and tuned energy levels induced by CA-D-A. Accordingly, the CA-D-A treated MAPbI3 -based PSCs exhibit higher open-circuit voltage and fill factor than the control PSC without any treatment, leading to improved power conversion efficiency (PCE) and enhanced device stability, especially the CAMA treated PSCs with an average PCE promoted from 17.77 (control PSCs) to 18.71%, and importantly an excellent PCE of 19.71% through further optimization. This work provides an effective strategy for developing highly efficient and stable PSCs with the assistance of both surface passivation and SGG.

Bifunctional interfacial engineering for piezo-phototronic enhanced photovoltaic performance of wearable perovskite solar cells

The piezo-phototronic effect can effectively modulate the energy band structure at the interface of p-n or metal-semiconductor junction, manipulating the separation, transport, and recombination of photoinduced charges. While zinc oxide (ZnO) is a good electron transporting layer (ETL), its Lewis's basic nature and presence of surface defects lead to deprotonation of perovskite, resulting in severe degradation of perovskite solar cells (PSC). Herein, the ZnO surface is converted to ZnS, which acts as a bifunctional interfacial layer, passivating the ZnO/perovskite interface by reducing the hydroxyl (‒OH) group on the ZnO surface for improved stability and forming strong coordination with Pb 2+ of perovskite (Zn-S-Pb pathway) and thus adjusting the energy level for efficient electron transport. Consequently, the power conversion efficiency (PCE) of the flexible PSC is remarkably improved from 12.94% to 14.68% under static external strain of 1.5%, ascribed to the strain-induced piezo-polarization charges, which modulate the energy band structure of ZnS/ZnO and ZnS/perovskite interfaces. As a result, spatial separation of photoinduced carriers is facilitated, reducing recombination probability. The energy band diagram is proposed to elucidate the mechanism. This strategy enables effective utilization of the piezo-phototronic effect while enhancing device stability. Power conversion efficiency and current density of flexible perovskite solar cell are enhanced from 12.94% and 21.82 mA cm −2 to 14.68% and 24.40 mA cm −2 , respectively, via a tensile strain of 1.5% due to the piezo-phototronic effect modulating the band structure at ZnO/ZnS and ZnS/perovskite interfaces. • A bifunctional interlayer at ZnO/perovskite interface is introduced for enhancing device stability. • Wearable PSCs with enhanced PCE is developed via the piezo-phototronic effect. • A 14% enhancement in PCE reaching 14.68% with 1.5% tensile strain is achieved. • PCE remains stable (90%) at 25 °C for 50 days and (84.2%) at 80 °C for 30 days. • A piezo-phototronic modulated energy band alignment mechanism for core-shell ETL is proposed.

In-Depth Comparative Study of the Cathode Interfacial Layer for a Stable Inverted Perovskite Solar Cell.

Achieving long‐term device stability is one of the most challenging issues that impede the commercialization of perovskite solar cells (PSCs). Recent studies have emphasized the significant role of the cathode interfacial layer (CIL) in determining the stability of inverted p‐i‐n PSCs. However, experimental investigations focusing on the influence of the CIL on PSC degradation have not been systematically carried out to date. In this study, a comparative analysis was performed on the PSC device stability by using four different CILs including practical oxides like ZnO and TiOx. A new implemented co‐doping approach was found to results in high device performance and enhanced device stability. The PSC with a thick film configuration of chemically modified TiOx CIL preserves over 77 % of its initial efficiencies of 17.24 % for 300 h under operational conditions without any encapsulation. The PSCs developed are among the most stable reported for methylammonium lead iodide (MAPbI3) perovskite compositions.

Charging Compensation Layer on Polyimide for Enhanced Device Stability in Flexible Technology

In this paper, we propose a structure that prevents the charging effects that occur in devices fabricated on polyimide (PI) substrates. In general, when fabricating a device on a PI substrate, an inorganic barrier layer is first deposited to prevent penetration of oxygen and moisture. In this study, we confirmed that fluorine ions were induced from PI by bias stress and proposed a SiOCH/SiO2 double layer as a barrier to prevent charging. Then, Al/PI/SiO2/Al and Al/ PI/SiOCH/SiO2/Al metal–insulator–metal capacitors were manufactured. The capacitor characteristics before and after application of bias stress were verified through current–voltage (I–V) and capacitance–voltage (C–V), which are electrical characterization methods, and secondary ion mass spectrometry (SIMS), which is a physical analysis method. As the voltage increased, the capacitance and current of the Al/PI/SiO2/Al capacitor varied, but those of the Al/PI/SiOCH/SiO2/Al device did not change. Finally, SIMS analysis confirmed that the PI-derived fluorine ions replaced the Si–CH3 bonds within the SiOCH film with Si–F bonds, thereby preventing capacitance and current fluctuations.

Reconfiguring the band-edge states of photovoltaic perovskites by conjugated organic cations.

The band edges of metal-halide perovskites with a general chemical structure of ABX3 (A, usually a monovalent organic cation; B, a divalent cation; and X, a halide anion) are constructed mainly of the orbitals from B and X sites. Hence, the structural and compositional varieties of the inorganic B-X framework are primarily responsible for regulating their electronic properties, whereas A-site cations are thought to only help stabilize the lattice and not to directly contribute to near-edge states. We report a π-conjugation-induced extension of electronic states of A-site cations that affects perovskite frontier orbitals. The π-conjugated pyrene-containing A-site cations electronically contribute to the surface band edges and influence the carrier dynamics, with a properly tailored intercalation distance between layers of the inorganic framework. The ethylammonium pyrene increased hole mobilities, improved power conversion efficiencies relative to that of a reference perovskite, and enhanced device stability.

S8 Additive Enables CsPbI2Br Perovskite with Reduced Defects and Improved Hydrophobicity for Inverted Solar Cells

Though prized for excellent thermal stability, inorganic perovskites are still behind organic/inorganic hybrid perovskites due to their high‐density defects and poor hydrophobicity. Herein, trace hydrophobic S8 is used as additive to optimize the solution‐processed CsPbI2Br perovskite film. A series of characterizations reveal that S8 additive not only leads to retarded crystallization of α‐CsPbI2Br perovskite at low temperature (<150 °C) via self‐formed Pb(S8)x2+ intermediate but also induces efficient grain‐boundary passivation via distinctive PbS coordination interaction and reduced wettability on perovskite surface, which all point to the formation of the perovskite film with reduced defects and improved hydrophobicity. As a result, the inverted perovskite solar cells (PSCs) based on the optimized all‐inorganic perovskite of CsPbI2Br:S8 deliver an increased power conversion efficiency (PCE) from 12.76% to 14.46% as well as remarkably enhanced device stability under thermal or ambient condition. This work thus provides a simple way as well as new insights for boosting the performance of solution‐processed all‐inorganic perovskite.

Conjugated polyelectrolyte doped perovskite films with enhanced photovoltaic performance and stability

Perovskite solar cells (PSCs) have achieved great success in the past few years because of outstanding photovoltaic performance. However, the existence of electronic trap states in the perovskite film is an obstacle for the fabrication of high-performance and stable PSCs. Herein, a linear conjugated polyelectrolyte was developed and employed as a dopant to improve the performance and stability of the perovskite film. The PPNNA doping can passivate surface defects to reduce the electronic trap states in the perovskite film, while simultaneously enhancing the electron extraction and transport to achieve high-efficiency solar cells. Furthermore, the PPNNA-doped perovskite film shows better stability from efficient surface passivation. The optimal 0.4% PPNNA-doped device exhibits better photovoltaic efficiency (20.38%) with enhanced device stability as compared to the control device (18.51%). This novel method by doping with the conjugated polyelectrolyte provides a pathway to fabricate high-efficiency and stable inverted PSCs.

Enhancing Built‐In Electric Field and Defect Passivation through Gradient Doping in Inverted CsPbI2Br Perovskite Solar Cells

Cesium‐based all‐inorganic perovskites (PVKs) are prized for their high thermal stability and wide bandgap suitable for the top layer of tandem solar cells. To further boost the photovoltaic performance of inorganic PVK solar cells (PeSCs), a variety of strategies aiming to either passivate defects or enhance the electric field are developed. Nevertheless, a double‐aim strategy is less explored. Herein, a facile strategy of gradient doping is adopted for optimizing the inverted CsPbI2Br PeSCs. Particularly, a bicationic iodine salt, namely 2,2′‐bis(trifluoromethyl)‐[1,1′‐biphenyl]‐4,4′‐diamine iodine (BFBAI2), is used to realize gradient doping in PVK and ZnO layers, respectively. As a result, the inverted PeSCs with the doped PVK/ZnO bilayer deliver improves power conversion efficiency (PCE) up to 14.38% along with enhanced device stability under ambient or thermal aging conditions, greatly surpassing the pristine devices. The improvements are attributed principally to the low‐defect PVK layer as well as enhanced electric field across the inverted PeSCs upon gradient doping. This work thus demonstrates an efficient bifunctional strategy toward highly efficient and stable CsPbI2Br PeSCs with inverted configuration.

Focussed Review of Utilization of Graphene-Based Materials in Electron Transport Layer in Halide Perovskite Solar Cells: Materials-Based Issues

The present work applies a focal point of materials-related issues to review the major case studies of electron transport layers (ETLs) of metal halide perovskite solar cells (PSCs) that contain graphene-based materials (GBMs), including graphene (GR), graphene oxide (GO), reduced graphene oxide (RGO), and graphene quantum dots (GQDs). The coverage includes the principal components of ETLs, which are compact and mesoporous TiO2, SnO2, ZnO and the fullerene derivative PCBM. Basic considerations of solar cell design are provided and the effects of the different ETL materials on the power conversion efficiency (PCE) have been surveyed. The strategy of adding GBMs is based on a range of phenomenological outcomes, including enhanced electron transport, enhanced current density-voltage (J-V) characteristics and parameters, potential for band gap (Eg) tuning, and enhanced device stability (chemical and environmental). These characteristics are made complicated by the variable effects of GBM size, amount, morphology, and distribution on the nanostructure, the resultant performance, and the associated effects on the potential for charge recombination. A further complication is the uncertain nature of the interfaces between the ETL and perovskite as well as between phases within the ETL.

Interface Modification Enabled by Atomic Layer Deposited Ultra‐Thin Titanium Oxide for High‐Efficiency and Semitransparent Organic Solar Cells

Organic solar cells (OSCs) are considered to have reached a second golden age with profoundly improved power conversion efficiency (PCE) and device stability in recent years. The modification of the interface layer plays a significant role in achieving performance enhancement in OSCs. Herein, the use of the atomic layer deposition (ALD) ultrathin TiOx to modify the interface layer in OSCs is reported. The modification with only two TiOx ALD cycles not only effectively passivates the interface between the ZnO electron transport layer (ETL) and the active layer, but also reduces the series resistance and improves the charge transport process in the device. An absolute 1% increase in PCE with enhanced device stability for modified OSCs is achieved. Semitransparent OSCs are also fabricated by applying this interface modification strategy. The modification with two TiOx ALD cycles increases the electrical device performance without affecting the optical properties of the semitransparent device. An average PCE of 10.46% with an average visible transmittance (AVT) of 19.61% and a color rendering index (CRI) close to 100 is demonstrated for the fabricated semitransparent device with the modification. The ALD‐assisted interface modification provides a straightforward way to realize high‐performance semitransparent OSCs.

Improved Radiation Sensing with Methylammonium Lead Tribromide Perovskite Semiconductors

Recently, organometallic halide perovskites (OMHPs) have attracted much interest as a potential medium resolution detector for ionizing radiation sensing applications. Despite moderate success in the development of OMHP radiation detectors to date, efforts to optimize bulk carrier properties are often hindered by device degradation caused by surface recombination, ionic conductivity, environmental instability, and interface phenomena. In this study, methods of improving the interfacial and surface properties, detector stability, and responsivity of methylammonium lead tribromide (MAPB) semiconductor radiation detectors were investigated. We demonstrated that chemomechanical polishing with dimethylformamide (DMF) as a finishing step decreased surface roughness, removed surface trap states, and greatly enhanced device stability compared to mechanical polishing. Further, using a tin oxide (SnO2) interface layer as hole blocking/electron transporting layer greatly increased the device fabrication success rate and helped mitigate the effect of ion migration reactions with metallic contacts. These post-growth processing techniques resulted in the first electron response of a MAPB detector exposed to alpha particles.

(Invited) Optimizing Material Systems for All-Inkjet-Printed Organic Thin-Film Transistors

Organic transistors have the advantages of mechanical flexibility and low-temperature printability, thus having attracted considerable attention. However, printed organic transistors typically underperform electrical characteristics and stability, which are usually worse in all-printed devices. Here, we demonstrate all-inkjet-printed organic transistors with a steep subthreshold slope of 60.4 mV/decade and good stability under bias stress, which were achieved by reducing trap density in the fabricated devices. The transistors showed good uniformity, with an average subthreshold slope of 62.4±14.0 mV/decade and an average threshold voltage of -0.042±0.026 V, which were superior to other reported organic transistors and thin-film device technologies.For all-inkjet-printed organic transistors, it is important to use a proper device structure to reduce device trap density. The traps in organic transistors can be found in semiconductor bulk materials and semiconductor/dielectric interfaces. We used small molecule materials for semiconductors that could generate large crystals and used polymers as the smooth bases for semiconductor/dielectric interfaces that could reduce interfacial traps. Given these considerations, the bottom-gate bottom-contact device architecture was chosen. The fabricated devices demonstrated a low density of states in the deep states of 6.59×1014 cm- 3 eV- 1. As a result, the devices showed such a steep subthreshold slope that approached the theoretical limit, and as well as a close-to-zero threshold voltage.Besides device architecture, we also present the significance of dielectric material selections to enhance device stability. It has been reported that using a fluoropolymer as the dielectric could significantly improve the stability of organic transistors. However, the issue of fluoropolymers is that they are too hydrophobic to print other functional materials on top of them. Thus, they cannot be used as a dielectric material for all-inkjet-printed transistors, since the dielectric is typically sandwiched by the gate and source/drain/semiconductor and there is an inevitable layer on top of the dielectric. Bipolar materials could be used to solve the printability issue, but they induce device instability. We found that a Lewis-acid monopolar polymer could solve these two issues at the same time. Due to the monopolar behavior, the polymer does not attract bipolar water molecules; due to its nature of being a Lewis acid, it wets common organic solvents that are mostly Lewis bases (such as ethanol, toluene, anisole). We compared two types of fabricated devices using poly-(4vinyl phenol) (bipolar) and polyvinyl cinnamate (Lewis-acid monopolar) as dielectrics. The two types of transistors demonstrated very similar static device characteristics, while the devices with polyvinyl cinnamate as the dielectric showed much superior bias-stress stability. Together with the advantage of trap density reduction, the fabricated all-inkjet-printed organic transistors demonstrated negligible changes in their electrical characteristics for one-year storage in the ambient (with a threshold voltage shift under 1 mV) or for one-hour bias stress (with a threshold voltage shift under 30 mV).Based on these transistors, we demonstrate an ultra-low-power amplifier with a high voltage gain for electrophysiology monitoring. The steep subthreshold slope gave the advantages of high intrinsic gain (> 1000 V/V) and high transconductance efficiency (38.2 S/A) in the subthreshold regime, where the devices operate with a low current at a sub-nanoampere level. As a result, a common-source amplifier showed a high voltage gain of 260 V/V, and more importantly ultra-low power consumption of < 1 nanowatt. We implemented this amplifier to track eye movements by monitoring electrooculogram signals. These signals were originally below 1 mV and amplified to around 0.3 V. This amplifier has the potential for subtle eyeball movement analysis and virtual and augmented reality.

Enhanced stability and photovoltaic performance of planar perovskite solar cells through anilinium thiobenzoate interfacial engineering

Organic-inorganic halide perovskite absorbers remain top contenders for current photovoltaic technologies owing to their ability to attain high efficiency at relatively low cost. However, commercialization of perovskite solar cells remains difficult due to their poor long-term stability. Such instability is commonly attributed to the ease in defect formation within the polycrystalline absorber film as well as at the surfaces between the layers, acting as recombination centers, reducing the overall performance of the device. Introduction of suitable interfacial layers has proven effective in defect passivation, allowing enhanced device stability and improving photovoltaic performance. In this study, a novel anilinium thiobenzoate (ATB) interlayer is deposited between the perovskite/hole transport layer (HTL) interface. Since ATB contains functional groups such as sulfur and ammonium, favourable coordination with under-coordinated lead ions on the perovskite film allows significant reduction in recombination losses and enhancement of open-circuit voltage from 1.05 to 1.11 V. Apart from the paramount efficiency of 19.33%, the 10 mg/mL ATB passivated device also shows exceptional long-term stability whereby 92% of initial efficiency is retained despite storage in ambient conditions for 150 days. Hence, results from this study highlights the importance of device passivation in attaining superior device performance and long-term stability.

Simultaneously enhanced moisture tolerance and defect passivation of perovskite solar cells with cross-linked grain encapsulation

Abstract The grain surfaces (film surface and grain boundary) of polycrystalline perovskite films are vulnerable sites in solar cells since they pose a high defect density and initiate the degradation of perovskite absorber. Achieving simultaneously defect passivation and grain protection from moisture is crucial for the viability of perovskite solar cells. Here, an in situ cross-linked grain encapsulation (CLGE) strategy that improves both device stability and defect passivation is reported. Cross-linkable semiconducting small molecules are mixed into the antisolvent to uniformly form a compact and conducting cross-linked layer over the grain surfaces. This cross-linked coating layer not only passivates trap states and facilitates hole extraction, but also enhances the device stability by preventing moisture diffusion. Using the CLGE strategy, a high power conversion efficiency (PCE) of 22.7% is obtained in 1.55-eV bandgap planar perovskite solar cells. The unencapsulated devices with CLGE exhibit significantly enhanced device stability again moisture and maintain >90% of their initial PCE after shelf storage under ambient condition for over 10,000 h.