Stable Perovskite Solar Cells Research Articles

Bimolecular Passivation-Dipole Bridge for Highly Efficient Inverted Perovskite Solar Cells with Low Nonradiative Recombination Loss.

Constructing charge-selective heterointerface with minimized defect state and matched energy level alignment is essential to reduce nonradiative recombination for achieving high-performance perovskite solar cells (PSCs). Herein, a bimolecular passivation-dipole bridge comprised of sodium phenylmethanesulfonate (SPM) and 2-phenylethylammonium iodide (PEAI) is carefully developed to regulate perovskite heterointerface. SPM passivates defect states and upshifts Fermi level (EF) of perovskite surface, and subsequent PEAI further induces additional negative dipole and causes the surface EF of perovskite pinning to negative polaron transport state of electron transport layer PCBM, which significantly promotes electron extraction at the perovskite electron-selective contact. These advantages are confirmed by a remarkably improved efficiency from 21.74% for control to 25.12% for treated PSC with excellent stability. Moreover, corresponding nonradiative recombination loss impressively diminishes from 123 to 70 meV, and charge transport-induced fill factor loss is only 3.00%. This work provides a promising approach via passivation-energetic synergy for engineering perovskite heterointerface toward highly efficient and stable PSCs.

Iodide Management and Oriented Crystallization Modulation for High-Performance All-Air Processed Perovskite Solar Cells.

Halide-related defects at the buried interface not only cause nonradiative recombination, but also seriously impair the long-term stability of perovskite solar cells (PSCs). Herein, a bottom-up, all-in-one modification strategy is proposed by introducing a multisite antioxidant ergothioneine (EGT) at the buried interface to manage iodide ions and manipulate crystallization dynamics. The findings demonstrate that EGT not only passivates uncoordinated Sn4+/Pb2+ defects, but also firmly anchors iodide ions and inhibits their oxidation to I2. Additionally, the modification by EGT enhances the oriented crystallization of perovskite, improves the carrier dynamics, and releases residual stresses. Consequently, the optimized all-air processed device (Rb0.02(FA0.95Cs0.05)0.98PbI2.91Br0.03Cl0.06) achieves a remarkable power conversion efficiency (PCE) of 25.13%, which is among the highest values reported for devices fabricated in air, along with ultrahigh open-circuit voltage (VOC) of 1.191V and fill factor (FF) of 84.9%. The optimized device without encapsulation exhibits strong humidity, thermal, and operational stability under ISOS protocol. Specifically, the initial efficiency of the device is retained at 90.12% after 1512 h of thermal ageing at 65°C and 90.14% after 930 h of continuous maximum power point tracking (MPPT) under simulated AM1.5 illumination.

π-Conjugation-Induced In Situ Nanoscale Ordering of Spiro-OMeTAD Boosts the Efficiency and Stability of Perovskite Solar Cells.

Spiro-OMeTAD hole transport materials typically exhibit an amorphous state in perovskite solar cells. However, the lack of structural ordering leads to weak intermolecular interaction, inferior carrier transfer, and poor stability in devices. Herein, we developed a π-conjugation-induced short-range ordering strategy to modulate the stacking order of spiro-OMeTAD during film formation. A clear molecular ordering at the nanoscale is observed, which enhances intermolecular π-π stacking in spiro-OMeTAD and enables effective carrier extraction and favorable energy level alignment. The nanoscale-ordered spiro-OMeTAD allows the achievement of perovskite solar cells with a champion efficiency of 25.37%, surpassing devices utilizing amorphous spiro-OMeTAD (23.52%). The unencapsulated device demonstrates enhanced operational stability by retaining 98% of its initial efficiency under continuous 1 sun equivalent illumination at 60 °C for 840 h. This work establishes a significant and valid modulation concept for the stacking order of organic transport materials, paving the way for the development of efficient and stable perovskite solar cells.

Surface Reaction Induced Compressive Strain for Stable Inorganic Perovskite Solar Cells

AbstractCesium‐based inorganic perovskites have emerged as promising light‐harvesting materials for perovskite solar cells (PSCs) due to their promising thermal‐ and photo‐stability. However, obstacles to commercialization remain regarding their phase instability. In this work, we report a facile and effective strategy to regulate the surface compressive strain via in situ surface reaction to stabilize CsPbI3 perovskite. The use of a chelating ligand with a molecular configuration closely matching the integer multiples of the unit cell lattice parameters of CsPbI3 induces compressive strain at the surface of CsPbI3. The chemical bonding and strain modulation synergistically not only passivate film defects, but also inhibit perovskite phase degradation, thus significantly improving the intrinsic stability of inorganic perovskite. Consequently, enhanced power conversion efficiency (PCE) of 21.0 % and 18.6 % were respectively achieved in 0.16‐cm2 lab‐scale devices and 25.3‐cm2 solar modules. Further, surface reaction enables PSCs with enhanced thermal and operational stability; these devices retain over 95 % of their initial PCE after damp‐heat tests (i.e., in 85 °C and 85 % R. H. air) for 2000 h, and remain 99 % of their initial PCE after operating for 2000 h, representing one of the most stable inorganic PSCs reported so far.

Synthesis of Multifunctional Organic Molecules via Michael Addition Reaction to Manage Perovskite Crystallization and Defect

AbstractAdditive engineering plays a pivotal role in achieving high‐quality light‐absorbing layers for high‐performance and stable perovskite solar cells (PSCs). Various functional groups within the additives exert distinct regulatory effects on the perovskite layer. However, few additive molecules can synergistically fulfill the dual functions of regulating crystallization and passivating defects. Here, we custom‐synthesized 2‐ureido‐4‐pyrimidone (UPy) organic small molecules with diverse functional groups as additives to modulate crystallization and defects in perovskite films via the Michael addition reaction. Theoretical and experimental investigations demonstrate that the −OH groups in UPy exhibit significant effects in fixing uncoordinated Pb2+ ions, passivation of lead‐iodide antisite defects, alleviating hysteresis, and reducing non‐radiative recombination. Furthermore, the enhanced C=O and −NH2 motifs interact with the A‐site cation via hydrogen bonding, which relieves residual strain and adjusts crystal orientation. This strategy effectively controls perovskite crystallization and passivates defects, ultimately enhancing the quality of perovskite films. Consequently, the open‐circuit voltage of the UPy‐based p‐i‐n PSCs reaches 1.20 V, and the fill factor surpasses 84 %. The champion device delivers a power conversion efficiency of 25.75 %. Remarkably, the unencapsulated device maintained 96.9 % and 94.5 % of its initial efficiency following 3,360 hours of dark storage and 1,866 hours of 1‐sun illumination, respectively.

Improved Charge‐Transfer Doping in Crystalline Polymer for Efficient and Stable Perovskite Solar Cells

AbstractPerovskite solar cells (PSCs) have significant potential for next‐generation photovoltaic technology applications. However, the instability of hole transport layers (HTLs) becomes the major obstacle to long‐term operational devices, which are affected by the intrinsic thermal instability and loose structure of hole transport materials, as well as the hygroscopicity and migration of dopants. Here, poly(3‐hexylthiophene‐2,5‐diyl) (P3HT) is used as a model crystalline polymer to thoroughly investigate effective p‐type doping strategies and the underlying mechanism. According to Hard–Soft‐Acid–Base theory, the soft base P3HT is more likely to form a stable Lewis acid–base adduct with the reactive soft acid radical, resulting in a strong charge‐transfer interaction, thereby enhancing conductivity and regulating the energy band of the HTL. Meanwhile, the radical cation salt can promote pre‐nucleation to optimize the crystallization orientation of P3HT. The resulting PSCs exhibited the efficiency of 25.16%, which is the highest efficiency reported so far based on doped P3HT. In addition, the resulting devices demonstrated excellent stability, maintaining 96.5%, 96%, and 91% of their initial efficiency after aging under continuous illumination for 2028 h, at 85 °C for 1080 h, and at maximum power point (MPP) tracking under continuous 1 Sun illumination at 85 °C for 528 h, respectively.

Enhanced optoelectronic characteristics of La-doped ZnO and its compatibility with Cs-doped MAPbI3 perovskite absorber material

Abstract The present study investigates the structural, electrical and optical characteristics of pristine and lanthanum (La)-doped zinc oxide electron transport layers (ETLs) fabricated by the sol gel method and their compatibility with Cs0.10MA0.90Pb(I0.9Br0.10)3 absorber layer for perovskite solar cells. All the ETLs were deposited under same deposition conditions, with the only difference in La percentage in the precursor solutions, ranging from 0 to 6%. X-ray diffraction (XRD) analysis demonstrated the presence of crystalline ZnO thin films and the absence of any impurity phases after La-doping. The calculated crystallite size, determined using Scherrer’s equation, increased from 11.13 to 21.76 nm after the introduction of dopant. The doping with 4% La led to the decrease in the optical bandgap from 3.32 eV of pristine ZnO to 3.23 eV. SEM analysis revealed better morphology of perovskite/4% La:ZnO specimen, which facilitated the absorbance and reduced the charge carrier recombination. It also exhibited superior resilience towards moisture and humidity which will eventually contribute to the development of more stable and efficient planar perovskite solar cells (PCSs).

Microscopic analysis of low but stable perovskite solar cell device performance using electron spin resonance

Perovskite solar cells have attracted much attention as next-generation solar cells. However, a typical hole-transport material, spiro-OMeTAD, has associated difficulties including tedious synthesis and high cost. To overcome these shortcomings, an easily synthesized and low-cost hole-transport material has been developed: HND-2NOMe. Although HND-2NOMe has high local charge mobility because of the quasi-planar structure, its lower device performance is a weak point, the cause of which has not yet been clarified. Here, we analyse the source of the lower performance by clarifying the internal states from a microscopic viewpoint using electron spin resonance. We observe hole diffusion from perovskite to HND-2NOMe under dark conditions, indicating hole barrier formation at the perovskite/HND-2NOMe interface, leading to lower performance. Although such a barrier is formed, less hole accumulation for the HND-2NOMe-based cells under solar irradiation occurs, which is related to the stable performance. The sources of the lower but stable performance are crucially important for providing guidelines for improving the device performance.

Efficient and stable inverted perovskite solar cells enabled by homogenized PCBM with enhanced electron transport

Fullerene derivatives are extensively employed in inverted perovskite solar cells due to their excellent electron extraction capabilities. However, [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) agglomerates easily in solution and exhibits a relatively low ionization barrier, increasing charge recombination losses and charge accumulation in the interface. Here, tetramethylthiuram disulfide (TMDS) is introduced into the PCBM solution to induce the formation of reducing sulfur radicals through UV light irradiation, allowing for n doping of the PCBM material. The resulting modified PCBM layer exhibits enhanced conductivity and electron mobility, significantly suppressing charge recombination. As a result, the resulting devices incorporating TMDS achieve a champion efficiency of 26.10% (certified 25.39%) and 24.06% at a larger area (1.0 cm2) with negligible hysteresis. More importantly, the optimized devices retain 95% and 90% of their initial efficiency after 1090 h under damp heat testing (85 °C and 85% relative humidity) and after 1271 h under maximum power point-tracking conditions, respectively.

Accelerating Additive-Assisted Defect Passivation via the Structural Isomer Effect for Highly Efficient and Stable Perovskite Solar Cells.

Defects in hybrid perovskites have hindered the development of highly efficient and stable hybrid perovskite solar cells (PSCs). Therefore, researchers have used additives to passivate defects in hybrid perovskites; however, detailed studies on multifunctional group additives with structural isomers are limited. In this letter, we report the improved defect passivation ability of additives through the structural isomer effect and enhanced photovoltaic performance using this effect. l-Alanine methyl ester hydrochloride (l-AMECl) and its structural isomer, β-AMECl, were used to understand the influence of structural variations in functional groups. The structural isomer β-AMECl effectively reduced the trap density in the hybrid perovskite, thereby enhancing the photovoltaic parameters. Consequently, we achieved a power conversion efficiency of 24.25% with β-AMECl, which is the best result among PSCs using additives. Additionally, the PSCs with β-AMECl maintained an initial efficiency of 94% over 2500 h at 25 °C and 25% relative humidity, showing improved long-term stability.

Modifying the buried interface by a sulfamate enable efficient perovskite solar cells with high stability

The buried interface between the pivotal perovskite layer and the electron transfer layer (ETL) greatly affects the photoelectric property of perovskite layer and the final performance of a perovskite solar cell (PSC). Effectively modifying the buried interface is feasible to improve the photoelectric conversion efficiency (PCE) and stability of PSCs. Herein, we employ a sulfamate sodium 4-aminoazobenzene-4′-sulfonate (SABS) with zwitterion to modify the SnO2 film surface to improve the performance of PSCs. The post-treatment makes the surface of SnO2 film smoother and also passivate the anion and cation vacancies of SnO2, which are benefit to the growth of perovskite crystals and strengthen the interface contact between SnO2 layer and perovskite layer. Furthermore, SABS molecules can passivate defects of perovskite layer at the buried interface. By using this post-treating method, the PCE of the final PSC is increased from 21.76 % to 23.86 %, and the storage and operational stability are also significantly improved. This promotion the buried interface via post-treating the SnO2 film with a zwitterion passivator provides a convenient strategy to effectively improve the performance and stability of PSCs.

Challenges and opportunities in high efficiency scalable and stable perovskite solar cells

Perovskite solar cells (PSCs) are the fastest-growing photovoltaic (PV) technology and hold great promise for the photovoltaic industry due to their low-cost fabrication and excellent efficiency. To achieve commercial readiness level, the most important factor would be yield beyond 95% at the PSC module levels. The current essential requirements for PSCs are reproducibility of high efficiency devices, scalability, and stability. The reported certified high efficiency (24–26%) results are based on the use of FAPbI3 perovskites with a bandgap of Eg≈ 1.5 eV, and the typical device's active area ranges from ≈ 0.1 cm2 to a maximum of 1 cm2. However, relatively higher bandgap PSCs are essential, especially in tandem solar cell applications. Hence, optimization of higher bandgap PSCs is a necessity. As the bandgap of the perovskites increases, the efficiency goes down due to reduced JSC and increased VOC loss. Therefore, understanding the loss mechanism and corresponding solutions need to be developed. Scaling up the device's active area without compromising the fill factor and, hence, efficiency is non-trivial. So, understanding the loss mechanism in large area devices is crucial. The stability analysis reported in the literature is inconsistent, preventing data comparison and identifying various degradation factors or failure mechanisms. Moreover, how the accelerated tests would be useful in predicting the real lifetime of the solar cells is yet to be developed. So, understanding the knowledge and the technological gaps between laboratory and industry-scale production is crucial for further development. Therefore, in this review article, we discuss the challenges and opportunities for scalable and stable high efficiency PSCs.

Multidentate Polymer-Stabilized Buried Interface for Efficient Planar Perovskite Solar Cells.

Buried interface engineering is crucial to improve the performance and stability of perovskite solar cells (PSCs). Although coordination materials have been widely used for buried interface modification, they are generally engineered on one surface of the interface through monodentate or bidentate molecules. Here, we propose that a multidentate polymer, sodium alginate (SA), acts with both surfaces via numerous C═O groups to reinforce buried interfaces. SA effectively reduces buried interface defects, adjusts the energy level alignment, and refines carrier dynamics. Notably, it also induces the growth of a perovskite film that is less tensile stressed and free of voids. Consequently, the champion device efficiency after SA treatment increased from 23.05% to 24.98%, along with significant improvements in both light and thermal stability. This work offers insights into efficiency and stability improvement from the perspective of multidentate polymer anchoring.

Dopant-Free Hole Transport Material Based on Non-Covalent Interaction for Efficient Perovskite Solar Cells.

Hole transport materials (HTMs) have a critical impact on the performance of perovskite solar cells (PSCs). Especially, the dopant-free HTMs could avoid the usage of hygroscopic dopants and reduce costs, which are important for device stability. Most of the current organic dopant-free HTMs are polycyclic aromatic hydrocarbons-based planar conjugated structures. Yet, the synthesis of conjugated fused heterocycles is often complicated. In this work, intramolecular non-covalent interaction is introduced to construct two organic HTMs (DCT and DTC), which can be facilely obtained through simple reactions. Compared to DTC with hexyl chain on the central benzene ring, DCT with hexyloxy chains shows better planarity in the core structure, as a result of the intramolecular non-covalent interactions between oxygen on hexyloxy and sulfur atom on the adjacent thiophene, as reflected from its single crystal structure. Moreover, DCT in a pristine state shows a decent hole mobility comparable to the doped Spiro-OMeTAD. Ultimately, conventional devices using dopant-free DCT as HTM show a high efficiency of 22.50%, with excellent long-term stability, and light and thermal stability. The results show that the noncovalent interaction is a useful and simple design strategy for dopant-free HTMs, that can effectively improve the efficiency and stability of PSCs.

Neutral Ligand Triggered Low-Dimensional Reconstruction for Improving the Efficiency and Stability of Perovskite Solar Cells

Neutral Ligand Triggered Low-Dimensional Reconstruction for Improving the Efficiency and Stability of Perovskite Solar Cells

Structurally Compact Penta(N,N-diphenylamino)corannulene as Dopant-free Hole Transport Materials for Stable and Efficient Perovskite Solar Cells.

Hole transport materials (HTMs) are essential for improving the stability and efficiency of perovskite solar cells (PSCs). In this study, we have designed and synthesized a novel organic small molecule HTM, cor-(DPA)5, characterized by a bowl-shaped core with symmetric five diphenylamine groups. Compared to already-known HTMs, the bowl-shaped and relatively compact structure of cor-(DPA)5 facilitates intermolecular π-π interactions, promotes film formations, and enhances charge transport. Consequently, the cor-[DPA(2)]5 HTM exhibits high charge mobility, exceptional hydrophobicity, and a significantly elevated glass transition temperature. Superior to previously reported HTMs such as spiro-OMeTAD and cor-OMePTPA, our newly synthesized cor-(DPA)5 HTM is free from any ionic dopants. As a result, the dopant-free cor-[DPA(2)]5-based PSC demonstrates an impressive efficiency of 24.01%, and exhibits outstanding operational stability. It retains 96% after continuous exposure to 1 sun irradiation for 800 hours under MPP (maximum power point) tracking in ambient air. These findings present a structurally compact novel HTM and exemplify a new approach to the molecular design of HTM for the development of stable and effective PSCs.

Structurally Compact Penta(N,N‐diphenylamino)corannulene as Dopant‐free Hole Transport Materials for Stable and Efficient Perovskite Solar Cells

Hole transport materials (HTMs) are essential for improving the stability and efficiency of perovskite solar cells (PSCs). In this study, we have designed and synthesized a novel organic small molecule HTM, cor‐(DPA)5, characterized by a bowl‐shaped core with symmetric five diphenylamine groups. Compared to already‐known HTMs, the bowl‐shaped and relatively compact structure of cor‐(DPA)5 facilitates intermolecular π–π interactions, promotes film formations, and enhances charge transport. Consequently, the cor‐[DPA(2)]5 HTM exhibits high charge mobility, exceptional hydrophobicity, and a significantly elevated glass transition temperature. Superior to previously reported HTMs such as spiro‐OMeTAD and cor‐OMePTPA, our newly synthesized cor‐(DPA)5 HTM is free from any ionic dopants. As a result, the dopant‐free cor‐[DPA(2)]5‐based PSC demonstrates an impressive efficiency of 24.01%, and exhibits outstanding operational stability. It retains 96% after continuous exposure to 1 sun irradiation for 800 hours under MPP (maximum power point) tracking in ambient air. These findings present a structurally compact novel HTM and exemplify a new approach to the molecular design of HTM for the development of stable and effective PSCs.

Reducing Interfacial Recombination in Inverted Perovskite Solar Cells With Selenophene-Substituted PCBM: Comparison With Thiophene and Furan Substitution.

Reducing the interfacial recombination and improving the charge transfer capability of charge transport layers are effective strategies to enhance the efficiency and stability of perovskite solar cells (PSCs). This study evaluates, for the first time, the effects of selenophene substitution in the chemical structure of phenyl-butyric acid methyl ester (PCBM) on the performance and stability of inverted PSCs. Selenophene substitution was compared to thiophene and furan substitutions, and the reference PCBM without chalcogenophene moiety. Additionally, this study investigates the differences between using the fullerene cages C70 and C60 in the PCBM chemical structure. The photovoltaic results demonstrate that, with an adequate control of the thickness of the electron transport layer (ETL), incorporating the selenophene moiety in the structures of fullerenes enhances the photovoltaic parameters of PSCs. This improvement results from the reduction in trap-assisted recombination, an increase in electron mobility, and the improved charge extraction processes. The use of C70, as opposed to C60, allows for the preparation of a series of ETLs with comparable thicknesses, although slightly lower efficiencies. This feature facilitates a systematic comparative analysis focused on variations in the electron properties of ETLs, thereby avoiding the inclusion of issues related to thickness and charge recombination processes.

Towards device stability of perovskite solar cells through low-cost alkyl-terminated SFX-based hole transporting materials and carbon electrodes

Developing cost-effective, high-efficiency, and stable hole transporting materials (HTMs) is crucial for replacing traditional spiro-OMeTAD in perovskite solar cells (PSCs) and achieving sustainable solar energy solutions. This work presents two novel air-stable HTMs based on a spiro[fluorene-9,9′-xanthene] (SFX) core functionalized with N-methylcarbazole (XC2-M) and N-hexylcarbazole (XC2-H) rings. These HTMs were synthesized via a straightforward, three-step process with good overall yields (∼40%) and low production costs. To further reduce device cost, carbon back electrodes were employed. The resulting PSCs, with a structure of FTO/SnO2/Cs0.05FA0.73MA0.22Pb(I0.77Br0.23)3/HTM/C achieved power conversion efficiencies (PCEs) of 13.5% (XC2-M) and 10.2% (XC2-H), comparable to the reference spiro-OMeTAD device (12.2%). The choice of alkyl chain on the HTM significantly impacts film morphology and device stability. The XC2-H device exhibited exceptional long-term stability, retaining approximately 90% of its initial PCE after 720 h of storage in 30–40% humidity air without encapsulation. This surpasses the performance of both the spiro-OMeTAD (55% retention) and XC2-M (68% retention) devices. The superior stability of XC2-H is attributed to its highly hydrophobic nature and the formation of a compact, smooth film due to interdigitation of the hexyl chains. The straightforward synthesis of XC2-H from commercially available materials offers a promising approach for large-scale PSC production.

Efficient and Stable Perovskite Solar Cells and Modules Enabled by Tailoring Additive Distribution According to the Film Growth Dynamics

HighlightsTwo pre-crystallization processes of gas quenching and vacuum quenching lead to different order of crystallization dynamics within the perovskite thin film, resulting in the differences of additive distribution.A tailor designed 1,3-bis(4-methoxyphenyl)thiourea was utilized to improve the buried interface, leading to a certified efficiency of 23.75% for blade-coated perovskite solar cell.The perovskite solar module (aperture area: 60.84 cm2) demonstrates an efficiency of 20.18% with excellent operational stability (maximum power point tracking of T90 > 1000 h).