Prolonged Carrier Lifetime Research Articles

Regulating Compressive Strain Enables High‐Performance Tin‐Based Perovskite Solar Cells

AbstractTin (Sn)‐based perovskites have emerged as promising alternatives to lead (Pb)‐based perovskites in thin‐film photovoltaics due to their comparable properties and reduced toxicity. Strains in perovskites can be tailored to modulate their optoelectronic properties, but mechanisms for the effects of strains on Sn‐based perovskite films and devices are unrevealed and corresponding strain engineering is unexplored. Herein, a strain engineering strategy is developed through incorporating 4‐fluorobenzylammonium halide salts (FBZAX, X = I, Br, Cl) into the perovskite precursor to regulate the strain effects in resultant Sn‐based perovskite films. It is found that a moderate level of compressive strain achieved by FBZABr alleviates the dislocations within perovskites to enhance carrier transport and reduces the defect density to prolong carrier lifetime. These improvements enable a champion efficiency exceeding 14% of Sn‐based perovskite solar cells with excellent operational stability.

Efficient Blade-Coated Wide-Bandgap and Tandem Perovskite Solar Cells via a Three-Step Restraining Strategy.

Blade-coating techniques have attracted significant attention for perovskite solar cells (PSCs)due to their high precursor utilization and simplicity. However, the power conversion efficiency (PCE) of blade-coated PSCs often lags behind that of spin-coated devices, mainly due to difficulties in precisely controlling perovskite film formation during pre-nucleation, heterogeneous nucleation, and crystallization in the blade-coating and N2-knife drying processes. In this work, a three-step restraining strategy is introduced utilizing functional glycine amide hydrochloride to regulate pre-nucleation clustering, suppress excessive heterogeneous nucleation, and decelerate crystallization, enabling comprehensive control of the perovskite film formation processes. This approach results in enlarged grains, reduced defect densities, and highly oriented crystalline wide-bandgap perovskite films with significantly prolonged carrier lifetimes, achieving a maximum PCE of 19.97% for 1.77 eV-bandgap blade-coated PSCs. Furthermore, two-terminal tandem cells, composed of wide-bandgap perovskite top cells and 1.25 eV-bandgap perovskite bottom cells fabricated via blade coating, yield an impressive PCE of 27.11% (stabilized at 26.87%). This study offers comprehensive insights into controlling pre-nucleation, heterogeneous nucleation, and crystallization during blade coating, providing valuable guidance for developing high-performance, large-area devices in the future.

Chiral Perovskite Nanowire Optoelectronic Synapse for Full‐Stokes Polarization‐Resolved Perception and Reservoir Computing

AbstractFull‐Stokes polarization‐resolved photonic artificial synapse (PAS) devices with in‐sensor computing capabilities show great potential for multimode vision perception and processing. However, current polarization‐resolved PAS devices are limited to monotonic recognition of linearly polarized light or circularly polarized light. Here, the study develops a chiral perovskite nanowire‐based PAS device as a full‐Stokes polarimeter to achieve polarization‐dependent neuromorphic optoelectronics. The device demonstrates a significantly high circular dichroism of over 400 millidegree and intrinsic linear dichroism, contributing to effectively sensing polarized light. Efficient charge separation at the perovskite NW/MXene heterostructure results in a prolonged carrier lifetime, thereby achieving a high responsivity of 2.3 AW−1, excellent synaptic behavior, and low power consumption of 0.5 pJ per synaptic stimuli. Significantly, the polarization‐modulated reservoir computing is developed based on the full‐Stokes PAS device, which exhibits a low normalized root mean square error of 0.023 in the chaotic system forecasting task. The single‐nanowire PAS device with the capability of sensing full‐Stokes parameters demonstrates great significance in building advanced energy‐efficient polarization‐resolved nanoscale neuromorphic vision systems.

Toward sustainable manufacturing of highly efficient and stable semi-transparent perovskite solar cells: The critical role of green solvent properties

Perovskite solar cells, promising a bright future in the energy market, are now being prioritized for high-throughput production to match their remarkable success at the laboratory scale. However, the use of toxic solvents proved to be one of the major constraints on scaling up production. Herein, a green solvent system consist of dimethyl sulfoxide (DMSO) and 1-dodecyl-3-methylimidazolium chloride ([C12MIM]Cl) ionic liquids (ILs) was developed to modulate the crystallization of wide-bandgap (WBG) perovskite films combined with a antisolvent-free process, i.e., nitrogen (N2) quenching method. The [C12MIM]Cl IL promoted the crystallization of WBG perovskite films with large grain sizes, reduced photo-active PbI2, modulated residual strain, prolonged carrier lifetimes as well as improved energy alignment. Consequently, the [C12MIM]Cl-modified single-junction 1.77 eV perovskite solar cells (PSCs) achieved a champion efficiency of 18.75 % with an excellent operational stability, retaining an initial PCE of 93 % after 2000 h of maximum-power-point tacking test. Meanwhile, the positive effect of the [C12MIM]Cl ILs was universal in perovskite with different bandgaps at 1.53, 1.68 and 1.72 eV, respectively. Furthermore, stacking semi-transparent [C12MIM]Cl-modified 1.77 eV WBG PSCs as top cells coupled with 1.27 eV OPV or 1.24 eV Sn-Pb PSC as bottom cells for the 4 T tandem configuration showed impressive PCE of 26.01 % and 27.44 %, respectively. This study opens a new avenue toward the sustainable fabrication of highly efficient and stable perovskite-based semitransparent and tandem solar cells.

One‐Step Aerosol Synthesis of Thiocyanate Passivated Hybrid Perovskite Microcrystals: Impact of (Pseudo‐)Halide Additives on Crystallization and Access to a Novel Binary Model

AbstractHybrid Perovskite materials have gone through an astonishing development due to their unique optoelectronic behavior, leading to the creation of a wide range of synthetic strategies. As the materials’ surface is found to play a crucial role with respect to the properties, e.g. hydration, stability and carrier mobilities, considerable efforts have been made to optimize the surface through various approaches. Especially the passivation of the perovskite surface attracted a lot of attention in this field, often resulting in more complex, multi‐step synthetic processes. In this study, a simple one‐step aerosol‐assisted synthetic approach is presented to obtain thiocyanate (SCN) passivated single‐crystal MAPbBr3 microcrystals. To elucidate the role of the additive in the crystallization process, mixed (pseudo‐)halide precursors are systematically investigated. The as processed, passivated microcrystals exhibit enhanced stability and charge carrier lifetimes. Additionally, a decrease in surface photovoltage, attributed to the presence of the SCN additive, is observed. Furthermore, the aerosol process is further developed resulting in a novel binary system containing MAPbBr3‐SCN perovskite microcrystals and Au nanostructures. This system serves as a promising model for further investigations into potential interactions between plasmonic and semiconducting materials, with initial results indicating prolonged charge carrier lifetimes.

Propylammonium chloride passivation for efficient carbon-electrode FA0.1MA0.9PbI3 solar cells

Carbon-based perovskite solar cells (C-PSCs) are garnering considerable attention in the photovoltaic realm due to their cost-effectiveness, simplified fabrication processes, and improved long-term durability. Nonetheless, their efficiency often suffers from notable non-radiative recombination at the interface of the carbon electrode and the perovskite layer, as well as inherent film defects. This investigation adopts additive engineering to address these challenges by introducing propylammonium chloride (PACl) into FA0.1MA0.9PbI3 perovskite films. The resultant films exhibit larger grain sizes and smoother surface morphology, mitigating grain boundary defects and enhancing interface quality. Additionally, PACl-treated films demonstrate heightened photoluminescence intensity and prolonged carrier lifetimes, effectively suppressing non-radiative recombination. Comparative analysis with control devices showcases a noteworthy efficiency boost in PACl-treated devices, rising from 14.74 % to 16.57 %, alongside minimal hysteresis effects and exemplary long-term stability. This study presents a simple yet highly efficient approach to enhance film morphology and rectify defects in perovskite films, leading to superior efficiency and stability in hole transport layer free C-PSCs.

Electron Transporting Polymeric Materials with Partial Quaternization for High-Performance Organic Solar Cells.

Efficient cathode interfacial layers (CILs) have become a crucial component of organic solar cells (OSCs). Charge extraction barriers, interfacial trap states, and significant transport resistance may be induced due to the unfavorable cathode interlayer, limiting the device performance. In this study, poly(4-vinylpyridine) is used as the CIL for OSCs, and a new type of CIL named P4VP-I is synthesized through the quaternization strategy. Compared to P4VP, P4VP-I CIL exhibits enhanced conductivity and optimized work function. OSCs employing the P4VP-I ETL demonstrate prolonged carrier lifetime, suppressed charge recombination, and achieve higher power conversion efficiencies (PCE) than the commonly used ETLs such as PFN-Br and Phen-NaDPO.

Anomalous Electroluminescence Characteristics of Perovskite Modules.

Spatially resolved photoluminescence (PL) and electroluminescence (EL) imaging technologies play a crucial role in evaluating the performance and stability of photovoltaic devices. However, their application in perovskite devices presents unique challenges. In this study, we report a discrepancy between the electrical performance of perovskite solar modules (PSMs) and the EL images. Following the application of a reverse bias voltage, we observed an increase in EL brightness associated with prolonged carrier lifetime and transport length. Furthermore, cross-sectional Kelvin probe force microscopy identified a significant potential increase primarily at the electron-transport layer (ETL) side after reverse bias, suggesting the presence of defective ETL/perovskite interfaces with filled hole traps. To address this EL mismatch, we proposed a mild reverse current recovery method aimed at aligning EL images with the cell performance without compromising device efficiency. This approach effectively mitigates discrepancies, ensuring alignment between the device performance and EL imaging. Our study underscores that caution is required when utilizing EL imaging to monitor spatial homogeneity in PSMs for future industrial production.

A universal hole transport layer for efficient organic solar cells processed by blade coating

Doctor-blade coating technology is a roll-to-roll compatible high-throughput thin film fabrication route. In this work, doctor-blading was applied for fabricating organic solar cells (OSCs) using a polyoxometalates material phosphomolybdic acid (PMA) as a hole transport layer (HTL). Compared to PEDOT:PSS, PMA-based devices demonstrate lower trap-assisted recombination, higher hole mobility, prolonged charge carrier lifetime and faster charge collection. With PM6:Y6 as active layer, PMA-based device delivered a high power conversion efficiency (PCE) of 17.79 % with a boosted short-circuit current density (JSC) value of 28.08 mA/cm2, which is one of the best performances for PM6:Y6-based solar cells through doctor-blading process. In addition, the performance improvement was observed in both conventional and inverted structured devices with various donor: acceptor combinations. These results indicate the high universality of PMA for printable processing and its prospect in preparation of the industrial production of OSCs.

Light-induced Kondo-like exciton-spin interaction in neodymium(II) doped hybrid perovskite

Tuning the properties of a pair of entangled electron and hole in a light-induced exciton is a fundamentally intriguing inquiry for quantum science. Here, using semiconducting hybrid perovskite as an exploratory platform, we discover that Nd2+-doped CH3NH3PbI3 (MAPbI3) perovskite exhibits a Kondo-like exciton-spin interaction under cryogenic and photoexcitation conditions. The feedback to such interaction between excitons in perovskite and the localized spins in Nd2+ is observed as notably prolonged carrier lifetimes measured by time-resolved photoluminescence, ~10 times to that of pristine MAPbI3 without Nd2+ dopant. From a mechanistic standpoint, such extended charge separation states are the consequence of the trap state enabled by the antiferromagnetic exchange interaction between the light-induced exciton and the localized 4 f spins of the Nd2+ in the proximity. Importantly, this Kondo-like exciton-spin interaction can be modulated by either increasing Nd2+ doping concentration that enhances the coupling between the exciton and Nd2+ 4 f spins as evidenced by elongated carrier lifetime, or by using an external magnetic field that can nullify the spin-dependent exchange interaction therein due to the unified orientations of Nd2+ spin angular momentum, thereby leading to exciton recombination at the dynamics comparable to pristine MAPbI3.

Boosting photoelectron transfer by Fermi and doping levels regulation in carbon nitride towards efficient solar-driven hydrogen production

The exploration of efficient photosystems with fast carrier dynamics is an important pursuit for solar conversion into hydrogen energy, while tremendous challenges remain since the intrinsic relationship between the band structure and the charge transfer behavior in semiconductors is still elusive. Towards this, P doped graphitic carbon nitride (P-g-C3N4) is fabricated as a prototype photocatalyst with P existing in P − N = C state. Through tuning the content of P to modulate the electronic donor concentration, the Fermi level of g-C3N4 is unidirectionally regulated from below to above the doping level induced by P. And it is revealed that the relative position of Fermi level vs. doping level plays a crucial role in determining the charge migration dynamics, where only a doping state near the Fermi level can act as the most efficient electron trap to prolong carrier lifetime. Accordingly, the precisely tailored P-g-C3N4 achieves a superior apparent quantum efficiency (AQE) of 5.7 % at 420 nm in overall water splitting that is among the highest levels of current photosystems. Our findings offer an innovative strategy for band structure regulation toward efficient photocatalysis.

Simultaneously Improving Stretchability and Efficiency of Flexible Organic Solar Cells by Incorporating a Copolymer Interlayer in Active Layer

AbstractMechanical stretchability is a vital criterion for the wearable application of organic solar cells (OSCs), while the excessive rigidity of fused‐ring small molecular acceptors make the photovoltaic film hard to meet the stretchable requirements. Herein, an effective strategy is developed to construct an intrinsically stretchable active layer by inserting copolymer PM6‐b‐PYSe as an interlayer between layer‐by‐layer processed D18 and BTP‐eC9. The copolymer interlayer shunts the penetration of BTP‐eC9 and facilitates an appropriate phase separation, favoring the enhanced crack onset strain of 17.69% compared to the D18/BTP‐eC9 film (9.67%). Combining with the optimal energy levels, prolonged carrier lifetime, and suppressed bimolecular recombination aroused by the incorporation of PM6‐b‐PYSe, the D18/PM6‐b‐PYSe/BTP‐eC9‐based OSC yields an encouraging efficiency of 17.97%. In particular, the device demonstrates excellent mechanical property, which can retain over 80% after 4000 bending cycles. This work provides an effective strategy to simultaneously enhance the intrinsic mechanical stretchability and photovoltaic performance of flexible OSCs.

Large and Small Polarons in Highly Efficient and Stable Organic‐Inorganic Lead Halide Perovskite Solar Cells: A Review

Polarons, which arise from the intricate interplay between excess electrons and/or holes and lattice vibrations (phonons), represent quasiparticles pivotal to the electronic behavior of materials. This review reaffirms the established classification of small and large polarons, emphasizing its relevance in the context of recent advances in understanding lead halide perovskites' behavior. The distinct characteristics of large and small polarons stem from the electron–phonon interaction range, which exerts a profound influence on materials’ characteristics and functionalities. Concurrently, lead halides have emerged with exceptional opto‐electronic properties, featuring prolonged carrier lifetimes, low recombination rates, high defect tolerance, and moderate charge carrier mobilities; these characteristics make them a compelling contender for integration of optoelectronic devices. In this review, the formation of both small and large polarons within the lattice of lead halide perovskites, elucidating their role in protecting photogenerated charge carriers from recombination processes, is discussed. As optoelectronic devices continue to advance, this review underscores the importance of unraveling polaron dynamics to pave the way for innovative strategies for enhancing the performance of next‐generation photovoltaic technologies. Future research should explore novel polaronic effects using advanced computational and experimental techniques, enhancing our understanding and unlocking new applications in materials science and device engineering.

Self‐Regulated Growth of Large‐Grain Sb2S3 Thin Films for High‐Efficiency Solar Cells

AbstractAntimony sulfide (Sb2S3) has attracted extensive attention due to its excellent photoelectric characteristics, including a high absorption coefficient (α > 104 cm−1) and a suitable bandgap (≈1.7 eV). However, due to its Q1D (quasi‐1D) structure, numerous deep‐level defects are identified in the Sb2S3 film, limiting the device's performance, and necessitating more efforts to overcome this situation. In this context, an ethanol solvent‐assisted chemical bath deposition (S‐CBD) strategy, a novel high‐quality thin film manufacturing technique is presented that modifies the supersaturation of the precursor solution by varying the boiling point and solvent polarity. This approach enables the effective regulation of the correlation between the crystal nucleation and growth rates, resulting in Sb2S3 films with large grains (≈4.25 µm, 37.5% ethanol), excellent crystallinity, well‐oriented structures (TC(211)/TC(020) = 2.39), low defect density, and prolonged carrier lifetimes (τAve ≈ 12.1 ns). Consequently, the final Sb2S3‐based solar device (FTO/CdS/Sb2S3/Spiro‐OMeTAD/Au) shows significant improvements in both FF (61.63%) and JSC (17.61 mA cm−2), yielding an excellent power conversion efficiency (PCE) of 7.84%. This research gives particular insights into the growth mechanism of high‐quality Sb2S3 thin films by CBD method as well as a potential route for enhancing Sb2S3 solar cell performance.

4-Methoxy phenethylammonium halide salts for surface passivation of perovskite films towards efficient and stable solar cells

Surface defects-mediated non-radiative charge recombination in polycrystalline perovskite films has been widely acknowledged to be responsible for the undesired open-circuit voltage (VOC) deficit, which is still a great challenge for perovskite solar cells (PSCs) to achieve the Shockley-Queisser efficiency limit. Herein, we report the use of 4-methoxy phenethylammonium halide salts (4-MeO-PEAX, X = I, Br, Cl) on the surface of formamidinium-cesium (FACs) perovskite films for surface passivation. The impact of halogen species in 4-MeO-PEAX on the quality of FACs perovskite films and device performance are comparatively investigated. We find that the prepared FACs perovskite films demonstrate dramatically reduced defect density and surface roughness, improved crystallinity, preferred (001) orientation and prolonged carrier lifetime after the post-treatment by 4-MeO-PEACl. Consequently, the 4-MeO-PEACl post-processed p-i-n PSCs have achieved a significantly improved power conversion efficiency of 22.63 % and VOC of 1.13 V. The unencapsulated devices post-treated with 4-MeO-PEACl maintained 90 %, 88 % and 84 % of their initial efficiencies, after being thermally stressed at 65 ℃ under dark for 312 h, stored in ambient air for 720 h and operated under continuous 1 sun equivalent illumination with maximum power point tracking at 50 ℃ for 1000 h, respectively.

Pyridine substitution strategy for one-dimensional perovskite: Toward efficient and stable mixed-dimensional photovoltaics

Surface passivation via one-dimensional (1D) perovskite has emerged as a promising method to suppress trap states and enhance charge extraction and transportation, leading to improved efficiency and long-term stability. Ionic liquid engineering, characterized as environmental-green additive, has shown particular promise in this regard. Herein, we explore the influence of the electronegativity and dipole moment of two different ionic liquids, benzamidine hydrochloride (BZ) and 2-amidinopyridine hydrochloride (2AP), on the formation of 1D perovskite and the performance of resulting devices. An effective passivation 1D layer has been formed through post-treatment, resulting in nano-rod crystal modified morphology with effectively passivated defects at grain boundaries, enhanced hydrophobicity, prolonged charge carrier lifetime, tailored energy level, and decreased trap density. Notably, the perovskite film treated with 2AP exhibited superior performance due to its stronger interaction with 3D perovskite and better passivation ability on defects originating from the presence of a pyridine ring. As a result, the PSCs incorporating 2AP achieved a champion power conversion efficiency of 24.55 % and retain 90 % of their initial efficiency after storage for over 1000 h at room temperature under ∼ 50 % RH conditions without encapsulation. This study provides valuable insights for expanding the selection of ionic liquids applied in 1D perovskite-assisted surface passivation towards efficient and stable photovoltaics.

Delocalizing Excitation for Highly‐Active Organic Photovoltaic Catalysts

AbstractLocalized excitation in traditional organic photocatalysts typically prevents the generation and extraction of photo‐induced free charge carriers, limiting their activity enhancement under illumination. Here, we enhance delocalized photoexcitation of small molecular photovoltaic catalysts by weakening their electron‐phonon coupling via rational fluoro‐substitution. The optimized 2FBP‐4F catalyst we develop here exhibits a minimized Huang–Rhys factor of 0.35 in solution, high dielectric constant and strong crystallization in the solid state. As a result, the energy barrier for exciton dissociation is decreased, and more importantly, polarons are unusually observed in 2FBP‐4F nanoparticles (NPs). With the increased hole transfer efficiency and prolonged charge carrier lifetime highly related to enhanced exciton delocalization, the PM6 : 2FBP‐4F heterojunction NPs at varied concentration exhibit much higher optimized photocatalytic activity (207.6–561.8 mmol h−1 g−1) for hydrogen evolution than the control PM6 : BP‐4F and PM6 : 2FBP‐6F NPs, as well as other reported photocatalysts under simulated solar light (AM 1.5G, 100 mW cm−2).

Delocalizing Excitation for Highly-Active Organic Photovoltaic Catalysts.

Localized excitation in traditional organic photocatalysts typically prevents the generation and extraction of photo-induced free charge carriers, limiting their activity enhancement under illumination. Here, we enhance delocalized photoexcitation of small molecular photovoltaic catalysts by weakening their electron-phonon coupling via rational fluoro-substitution. The optimized 2FBP-4F catalyst we develop here exhibits a minimized Huang-Rhys factor of 0.35 in solution, high dielectric constant and strong crystallization in the solid state. As a result, the energy barrier for exciton dissociation is decreased, and more importantly, polarons are unusually observed in 2FBP-4F nanoparticles (NPs). With the increased hole transfer efficiency and prolonged charge carrier lifetime highly related to enhanced exciton delocalization, the PM6 : 2FBP-4F heterojunction NPs at varied concentration exhibit much higher optimized photocatalytic activity (207.6-561.8 mmol h-1 g-1) for hydrogen evolution than the control PM6 : BP-4F and PM6 : 2FBP-6F NPs, as well as other reported photocatalysts under simulated solar light (AM 1.5G, 100 mW cm-2).

Chiral Covalent Organic Framework Films with Enhanced Photoelectrical Performances.

The desirable superimposed stacking of two-dimensional covalent organic frameworks (2D COFs) benefits out-of-plane charge transfer, whereas the actual stacking deviation cannot leverage the potential of 2D COFs for optoelectrical applications. Herein, we report a chirality-induced strategy to control the parallel AA-stacking sequence for the β-ketoenamine-linked COF film supported on a FTO substrate. The resulting chiral modules are periodically distributed at the framework node, ensuring identical mirrored configurations of layers for parallel stacking. Such unique architectonics exhibit the prolonged charge carrier lifetime, fast charge-transfer dynamics, and ultrahigh electron collection efficiency, thereby allowing for the excellent photocurrent response of 38 μA/cm2 at 0.25 V (vs RHE). The origin of superior performances lies in the intensified exciton gradient distribution and electron density for photoinduced electron-hole dissociation and charge transfer, in stark contrast to achiral analogues. This study highlights the stacking sequence regulated by chiral nanoarchitectonics and promises great potential of chiral COFs in photoelectrical catalysis.

Effects of Surface Defects on Performance and Dynamics of CsPbI2Br Perovskite: First-Principles Nonadiabatic Molecular Dynamics Simulations.

Inorganic mixed-halogen perovskites exhibit excellent photovoltaic properties and stability; yet, their photoelectric conversion efficiency is limited by inherent surface defects. In this work, we study the impact of defects on properties of CsPbI2Br slabs using first-principles calculations, focusing on specific defects such as I vacancy (VI), I interposition (Ii), and I substitution by Pb (PbI). Our findings reveal that these defects affect the geometric and optoelectronic properties as well as dynamics of charge carriers of slabs. We employ two theoretical frameworks (surface hopping and Redfield theory) of nonadiabatic molecular dynamics simulations to comprehensively study relaxation processes and obtain consistent results. The presence of VI reduces carrier lifetimes, while the influence of PbI on carrier lifetimes is negligible. In contrast, Ii defects lead to prolonged carrier lifetimes. These insights provide valuable guidance for the rational design of perovskite photovoltaic devices, aiming to enhance their efficiency and stability.