Halide Perovskite Solar Cells Research Articles

Quantifying recombination and charge carrier extraction in halide perovskites via hyperspectral time-resolved photoluminescence imaging

Identifying sources of nonradiative recombination and quantifying charge carrier extraction in halide perovskite solar cells are important in further developing this thin-film technology. Steady-state and time-resolved photoluminescence (TRPL), in combination with analytical modeling, have emerged as non-destructive tools to achieve the desired results. However, the exact location of the recombination and charge carrier extraction losses in devices is often obscured by various competing processes when photoluminescence measurements are analyzed. Here, we show via absolute-photon-calibrated hyperspectral photoluminescence and TRPL imaging how surface passivation and inhomogeneities at interfaces impact the photoluminescence quantum yields and minority carrier lifetimes. Laser illumination from the perovskite and glass/TiO2 sides allows us to disentangle changes in surface recombination velocity from the charge carrier extraction at the electron transport layer. We find that charge extraction is spatially modulated due to an inhomogeneous mesoporous (mp)-TiO2 film thickness. Our results show that the mp-TiO2 layer is not fully optimized since the electronic properties are spatially modified, leading to lateral changes in quasi-Fermi-level splitting, minority carrier lifetime and, consequently, a reduction in open-circuit voltage.

Passivating defects in SnO2 electron transport layer through SnF2 incorporation in perovskite solar cells

Metal halide perovskite solar cells have received a lot of attention from researchers because of their excellent performance, and their efficiency has increased rapidly over the past decade and is now comparable to that of conventional crystalline silicon solar cells. Perovskite solar cells (PSCs) are currently most commonly constructed with SnO2 as an electron transport layer (ETL). Nevertheless, its existence of bulk phase defects and surface defects pose an impediment to developing a higher level as the most favorable electron transport layer. This paper suggests an efficient technique to decrease the defects of SnO2 through incorporating a metal halide SnF2 in planar (n-i-p type) perovskite solar cells. Divalent Sn in SnF2 is easily oxidized to tetravalent Sn, leading to more conversion of divalent Sn to tetravalent Sn, which inhibits the formation of oxygen vacancies from the source. F replaces defective sites, passivates oxygen vacancy defects, and reduces the content of hydroxyl oxygen on the surface. Doping SnF2 enhances the conduction band value and conductivity of SnO2, making the energy levels of the ETL and perovskite interfaces more compatible. This eliminates energy barriers in charge transport. Consequently, the fill factor of planar PSCs that were prepared through SnO2:SnF2 ETL exhibited an increase from 80.01% to 82.12%. Furthermore, the efficiency of PCE underwent an improvement from 21.43% to 22.65%.

Hybrid Organic-Inorganic ZnO/PCBM Electron Transport Layer with Organic Lead Halide Perovskite Solar Cell Materials CH3NH3PbIX2, X is Cl or I

An experimental investigation has been undertaken to explore a variety of properties of organic perovskite solar cells (OPSCs) that are distinct in their photovoltaic response. In this study, OPSCs were constructed using zinc oxide, ZnO and [6,6]-phenylC[Formula: see text]-acid methyl ester, PCBM, as electron transfer materials (ETM), poly(3-hexylthiophene), P3HT, as hole transport material (HTM), and CH3NH3PbIX2 as a photosensitizer, where X is either Cl or I. The structural and optical characteristics of the ETM and HTM layers and the perovskite materials of OPSCs were investigated. The [Formula: see text]–[Formula: see text] and [Formula: see text]–[Formula: see text] curves of each solar cell prepared in OPSCs were measured using an integrated cell tester. This comprises a photovoltaic [Formula: see text]–[Formula: see text] measurement system and a solar simulation system. As a result of these results, the OPSC’s performance is evaluated. The calculations in this work suggest that the highest power conversion efficiency (PCE = 6.31%) was achieved in photovoltaic devices using CH3NH3PbI3 as the effective absorber layer and ZnO with PCBM as the ETM layer. At a light intensity of 100 mW/cm2, each OPSC cell was performed. Under the same conditions, the [Formula: see text]–[Formula: see text] curves were evaluated for each OPSC device. By improving the selection of organic and inorganic active materials in the ETM layer, OPSC performance may be improved.

Unraveling Interface-Driven and Loss Mechanism-Centric Phenomena in 3D/2D Halide Perovskites: Prospects for Optoelectronic Applications.

In recent years, organic-inorganic metal halide perovskite solar cells (PSCs) have attracted considerable interest due to their remarkable and rapidly advancing efficiencies. Over the past decade, PSC efficiencies have significantly approached those of state-of-the-art silicon-based photovoltaics, making them a promising material. Currently, the scientific community widely recognizes the performance of 3D-PSCs and 2D-PSCs individually. However, when both are combined to form a heterostructure, the lattice and charge dynamics at the interface undergo a multitude of mechanisms that affect their performance. The interface between heterostructures facilitates the degradation of PSCs. The degradation pathways can be attributed to lattice distortions, inhomogeneous energy landscapes, interlayer ion migration, nonradiative recombination, and charge accumulation. This Review is dedicated to examining the phenomena that arise at the interface of 3D/2D halide perovskites and their related photophysical properties and loss mechanism processes. We mainly focus on the impact of lattice mismatch, energy level alignment, anomalous carrier dynamics, and loss mechanisms. We propose a "cause-impact-identify-rectify" approach to gain a comprehensive understanding of the ultrafast processes occurring within the material. Finally, we highlight the importance of advanced spectroscopic and imaging techniques in unraveling these intricate mechanisms. This discussion delves into the future possibilities of fabricating 3D/2D heterostructure-based optoelectronic devices, pushing the boundaries of performance across diverse fields. It envisions the creation of devices with unparalleled capabilities, exceeding the limitations of current technologies.

Limitations and Progresses in Carbon-Based Cesium Lead Halide Perovskite Solar Cells.

Inorganic cesium lead halide perovskites (CsPbIx Br3-x , 0≤x≤3) are promising alternatives with great thermal stability. Additionally, the choice of moisture-resistive and dopant-free carbon as the electrode material can simultaneously solve the problems of stability and cost. Therefore, carbon electrode-based inorganic PSCs (C-IPSCs) represent a promising candidate for commercialization, yet both the efficiencies and stability of related devices demand further progress. This article reviews the recent advancement of C-IPSCs and then unravels the distinctive merits and limitations in this field. Subsequently, our perspective on various modification strategies is analyzed on a methodological level. Finally, this article outlooks the promising research contents and the remaining unresolved issues in this field. We believe that understanding and analyzing the related problems in this field are instructive to stimulate the future development of C-IPSCs.

Recent Advancements in Enhancing Interfacial Charge Transport for Perovskite Solar Cells

Finding the most suitable pathways to improve the interfacial charge transportation in lead halide perovskite solar cells is a highly desirable research area to enhance device performance and enable commercialization. The complexities of interfacial charge dynamics, encompassing separation, diffusion, and collection processes, pivot on the thoughtful selection of interlayers and their inherent properties. Challenges arise from nonideal interfaces characterized by mismatched energy levels and defects that hinder efficient charge transport. To address these concerns, implementing tailored interfacial engineering strategies, including interlayer modification, band alignments, and passivation techniques, can help mitigate unwanted nonradiative recombination. This review aims to elucidate the impact of trap states on suppressing charge transport in the device, along with subsequent passivation techniques designed to enhance interfacial charge transport. Following that, a comprehensive overview is presented, highlighting recent advancements in interface engineering techniques that improve interfacial properties between the electron transport layer/perovskite and perovskite/hole transport layer. Significantly, the impact of using buffer and dipole layers as interlayers on overall device performance and stability is investigated.

Multi-Functional Spirobifluorene Phosphonate Based Exciplex Interface Enables Voc Reaching 95% of Theoretical Limit for Perovskite Solar Cells.

Metal halide perovskite solar cells (PSCs) show significant advancements in power conversion efficiency (PCE). However, the open-circuit voltage (VOC) of PSCs is limited by interfacial factors such as defect-induced recombination, energy band mismatch, and non-intimate interface contact. Here, an exciplex interface is first developed based on the strategically designed and synthesized two spirobifluorene phosphonate molecules to mitigate VOC loss in PSCs. The exciplex interface constructed by the intimate contact between the multi-functional molecules and hole transport layer takes the roles to promote the hole extraction by donor-acceptor interaction, passivate coordination-unsaturated Pb2+ defects by equipped phosphonate groups, and optimize the energy level alignment. As a result, a record VOC of 1.26V with a perovskite bandgap of 1.61eV is achieved, representing over 95% of theoretical limit. This advancement leads to an increase in PCE from 21.29% to 24.12% and improved stability. The exciplex interface paves the way for addressing the long-standing challenge of VOC loss and promotes the wider application of PSCs.

Progress on Electron Transport Layers for Perovskite Solar Cells

The photovoltaic industry is very interested in designing and developing next-generation device architectures using organic-inorganic perovskite hybrid solar cell materials. In fact, perovskites represent one of the most promising materials for high efficiency, low-cost solar cells. This is most apparent in the power conversion efficiency of perovskite solar cells (PSCs) going from 3.8 to 24.2 % in recent years. One of the primary challenges of developing PSC’s however is the realization of an appropriate electron transport layer. As such, this review focuses on recent developments in the electron transport layer (ETL) of perovskite solar cells. It examines and summarises designs, electron transport layers and perovskite active layers for efficient perovskite solar cells. The performance and stability issues with organic-inorganic halide perovskite solar cells are also discussed with some recommendations for additional research on the ETL and perovskite active layer were offered.

Defect passivation in methylammonium/bromine free inverted perovskite solar cells using charge-modulated molecular bonding

Molecular passivation is a prominent approach for improving the performance and operation stability of halide perovskite solar cells (HPSCs). Herein, we reveal discernible effects of diammonium molecules with either an aryl or alkyl core onto Methylammonium-free perovskites. Piperazine dihydriodide (PZDI), characterized by an alkyl core-electron cloud-rich-NH terminal, proves effective in mitigating surface and bulk defects and modifying surface chemistry or interfacial energy band, ultimately leading to improved carrier extraction. Benefiting from superior PZDI passivation, the device achieves an impressive efficiency of 23.17% (area ~1 cm2) (low open circuit voltage deficit ~0.327 V) along with superior operational stability. We achieve a certified efficiency of ~21.47% (area ~1.024 cm2) for inverted HPSC. PZDI strengthens adhesion to the perovskite via -NH2I and Mulliken charge distribution. Device analysis corroborates that stronger bonding interaction attenuates the defect densities and suppresses ion migration. This work underscores the crucial role of bifunctional molecules with stronger surface adsorption in defect mitigation, setting the stage for the design of charge-regulated molecular passivation to enhance the performance and stability of HPSC.

Microencapsulated Perovskite Crystals via In Situ Permeation Growth from Polymer Microencapsulation-Expansion-Contraction Strategy: Advancing a Record Long-Term Stability beyond 10000 h for Perovskite Solar Cells.

Organic metal halide perovskite solar cells (PSCs) bearing both high efficiency and durability are predominantly challenged by inadequate crystallinity of perovskite. Herein, a polymer microencapsulation-expansion-contraction strategy is proposed for the first time to optimize the crystallization behavior of perovskite, typically by adeptly harnessing the swelling and deswelling characteristics of poly(4-acryloylmorpholine) (poly(4-AcM)) network on PbI2 surface. It can effectively retard the crystallization rate of perovskite, permitting meliorative crystallinity featured by increased grain size from 0.74 to 1.32µm and reduced trap density from 1.12 × 1016 to 2.56 × 1015 cm-3. Moreover, profiting from the protection of poly(4-AcM) microencapsulation layer, the degradation of the perovskite is markedly suppressed. Resultant PSCs gain a robust power conversion efficiency (PCE) of 24.04%. Typically, they maintain 91% of their initial PCE for 13008 h in a desiccated ambient environment and retain 92% PCE after storage for 4000 h with a relative humidity of 50 ± 10%, which is the state-of-the-art long-term stability among the reported contributions.

Physically and Chemically Stable Molybdenum-Based Composite Electrodes for p-i-n Perovskite Solar Cells.

Metal halide perovskite solar cells (PSCs) have garnered much attention in recent years. Despite the remarkable advancements in PSCs utilizing traditional metal electrodes, challenges such as stability concerns and elevated costs have necessitated the exploration of innovative electrode designs to facilitate industrial commercialization. Herein, a physically and chemically stable molybdenum (Mo) electrode is developed to fundamentally tackle the instability factors introduced by electrodes. The combined spatially resolved element analyses and theoretical study demonstrate the high diffusion barrier of Mo ions within the device. Structural and morphology characterization also reveals the negligible plastic deformation and halide-metal reaction during aging when Mo is in contact with perovskite (PVSK). The electrode/underlayer junction is further stabilized by a thin seed layer of titanium (Ti) to improve Mo film's uniformity and adhesion. Based on a corresponding p-i-n PSCs (ITO/PTAA/PVSK/C60/SnO2/ITO/Ti/Mo), the champion sample could deliver an efficiency of 22.25%, which is among the highest value for PSCs based on Mo electrodes. Meanwhile, the device shows negligible performance decay after 2000 h operation, and retains 91% of the initial value after 1300 h at 50-60 °C. In summary, the multilayer Mo electrode opens an effective avenue to all-round stable electrode design in high-performance PSCs.

Simultaneous Interfacial Defect Passivation and Bottom-Up Excess PbI2 Management via Rubidium Chloride in Highly Efficient Perovskite Solar Cells with Suppressed Hysteresis.

In halide perovskite solar cells (PSCs), moderate lead iodide (PbI2) can enhance device efficiency by providing some passivation effects, but extremely active PbI2 leads to the current density-voltage hysteresis effect and device instability. In addition, defects distributed on the buried interface of tin oxide (SnO2)/perovskite will lead to the photogenerated carrier recombination. Here, rubidium chloride (RbCl) is introduced at the buried SnO2/perovskite interface, which not only acts as an interfacial passivator to interact with the uncoordinated tin ions (Sn4+) and fill the oxygen vacancy on the SnO2 surface but also converts PbI2 into an inactive (PbI2)2RbCl compound to stabilize the perovskite phase via a bottom-up evolution effect. These synergistic effects deliver a champion PCE of 22.13% with suppressed hysteresis for the W RbCl PSCs, in combination with enhanced environmental and thermal stability. This work demonstrates that the interfacial defect passivation and bottom-up excess PbI2 management using RbCl modifiers are promising strategies to address the outstanding challenges associated with PSCs.

Long-chain organic molecules enable mixed dimensional perovskite photovoltaics: a brief view.

The remarkable optoelectronic properties of organometal halide perovskite solar cells have captivated significant attention in the energy sector. Nevertheless, the instability of 3D perovskites, despite their extensive study and attainment of high-power conversion efficiency, remains a substantial obstacle in advancing PSCs for practical applications and eventual commercialization. To tackle this issue, researchers have devised mixed-dimensional perovskite structures combining 1D and 3D components. This innovative approach entails incorporating stable 1D perovskites into 3D perovskite matrices, yielding a significant improvement in long-term stability against various challenges, including moisture, continuous illumination, and thermal stress. Notably, the incorporation of 1D perovskite yields a multitude of advantages. Firstly, it efficiently passivates defects, thereby improving the overall device quality. Secondly, it retards ion migration, a pivotal factor in degradation, thus further bolstering stability. Lastly, the inclusion of 1D perovskite facilitates charge transport, ultimately resulting in an elevated device efficiency. In this succinct review, we thoroughly encapsulate the recent progress in PSCs utilizing 1D/3D mixed-dimensional architectures. These advancements encompass both stacked bilayer configurations of 1D/3D structures and mixed monolayer structures of 1D/3D. Additionally, we tackle critical challenges that must be surmounted and offer insights into the prospects for further advancements in this domain.

Effects of MgF2 anti-reflection coating on optical losses in metal halide perovskite solar cells

The importance of light management for perovskite solar cells (PSCs) has recently been emphasized because their power conversion efficiency approaches their theoretical thermodynamic limits. Among optical strategies, anti-reflection (AR) coating is the most widely used method to reduce reflectance loss and thus increase light-harvesting efficiency. Monolayer MgF2 is a well-known AR material because of its optimal refractive index, simple fabrication process, and physical and chemical durabilities. Nevertheless, quantitative estimates of the improvement achieved by the MgF2 AR layer are lacking. In this study, we conducted theoretical and experimental evaluations to assess the AR effect of MgF2 on the performance of formamidinium lead-triiodide PSCs. A sinusoidal tendency to enhance the short-circuit current density (J SC) was observed depending on the thickness, which was attributed to the interference of the incident light. A transfer matrix method-based simulation was conducted to calculate the optical losses, demonstrating the critical impact of reflectance loss on the J SC improvement. The predicted J SCs values, depending on the perovskite thickness and the incident angle, are also presented. The combined use of experimental and theoretical approaches offers notable advantages, including accurate interpretation of photocurrent generation, detailed optical analysis of the experimental results, and device performance predictions under unexplored conditions.

Inductive and Capacitive Hysteresis of Current-Voltage Curves: Unified Structural Dynamics in Solar Energy Devices, Memristors, Ionic Transistors, and Bioelectronics

Hysteresis observed in the current-voltage curves of both electronic and ionic devices is a phenomenon where the curve's shape is altered on the basis of the measurement speed. This effect is driven by internal processes that introduce a time delay in the response to an external stimulus, leading to measurements being dependent on the history of the past disturbances. This hysteresis effect has posed challenges, particularly in solution-processed photovoltaic devices such as halide perovskite solar cells, where it significantly complicates the evaluation of performance quality. In other devices, such as memristors and organic electrochemical transistors for neuromorphic applications, hysteresis is an inherent aspect of their functionality, facilitating transitions between different conductivity states. Natural and artificial ionically conducting channels also exhibit pronounced hysteresis, a crucial component for generating action potentials in neurons. In this study, we aim to categorize various forms of hysteresis by identifying shared elements among diverse physical, chemical, and biological conducting systems. Our method involves examining hysteresis from multiple angles, using simplified models that capture essential response types. We analyze system behavior using techniques such as linear sweep voltammetry and impedance spectroscopy and transient currents resulting from small voltage steps. Our investigation reveals two primary hysteresis types based on how current responds to rapid sweep rates: capacitive hysteresis and inductive hysteresis. These terms correspond to the dominant component in the equivalent circuit, determining the transient time response. Remarkably, these concepts provide insights into vastly different systems, spanning solar cells, capacitors, transistors, electrofluidic nanopores, and protein ion channels. The consistency in electrical responses across the different cases enables the identification of the primary cause of hysteresis. We also elucidate the frequency dependence of hysteresis and the stepwise responses of solar cells, illustrating how fundamental relaxations contribute to the overall surplus or deficit of current during extensive voltage sweeps that define the current-voltage curve. Published by the American Physical Society 2024

Passivating A-Site and X-Site Vacancies Simultaneously via N-Heterocyclic Amines for Efficient Cs2AgBiBr6 Solar Cells.

To address the toxicity and stability issues of traditional lead halide perovskite solar cells (PSCs), the development of lead-free PSCs, such as Cs2AgBiBr6 solar cells, is of great significance. However, due to the low defect formation energy of Cs2AgBiBr6, a large number of vacancies, including A-site vacancies and X-site vacancies, form during the fabrication process of the Cs2AgBiBr6 film, which seriously damage the performance of the devices. The traditional phenylethylammonium (PEA) cation, mainly focusing on passivating A-site vacancies, is incapable of reducing X-site vacancies and so results in a limited performance improvement in Cs2AgBiBr6 solar cells. Herein, inspired by the capability of the Lewis base to coordinate with metal cations, a series of N-heterocyclic amines are introduced to serve as a dual-site passivator, reducing A-site and X-site vacancies at the same time. The highest power conversion efficiency of modified Cs2AgBiBr6 solar cells has been increased 36% from 1.10 to 1.50%. Further investigation reveals that the higher electron density of additives would lead to a stronger interaction with metal cations like Ag+ and Bi3+, thus reducing more X-site defects and improving carrier dynamics. Our work provides a strategy for passivating perovskite with various kinds of defects and reveals the connection between the coordination capability of additives and device performance enhancement, which could be instructive in improving the performance of lead-free PSCs.

Recent developments in perovskite materials, fabrication techniques, band gap engineering, and the stability of perovskite solar cells

Organic-inorganic hybrid metal halide perovskite solar cells (PSC) represent a novel class of optoelectronic semiconductors that have garnered significant attention from photovoltaic researchers globally. This is due to their continually improving efficiency, straightforward solution processing methods, use of lightweight and cost-effective materials, and other notable features. The advantageous properties of perovskite materials, such as superior charge transport, tunable band gap, and distinctive electronic structure, contribute to their appeal. Over the past 6 to 7 years, diverse device architectures and fabrication techniques for PSC have emerged, achieving an impressive power conversion efficiency (PCE) of 25.7%. This review article primarily focuses on recent advancements in PSC fabrication techniques, synthesis, device architecture, charge transport mechanisms, band gap engineering, and stability. Additionally, it provides a summary of recently reported materials used in various layers of PSC, including the perovskite layer, as well as electron and hole transport layers. Lastly, the article outlines the challenges faced in the development of PSC, offers recommendations, and suggests potential directions for future research to guide the field forward.

3-Thiophenemalonic Acid Additive Enhanced Performance in Perovskite Solar Cells.

The development of ambient-air-processable organic-inorganic halide perovskite solar cells (OIHPSCs) is a challenge necessary for the transfer of laboratory-scale technology to large-scale and low-cost manufacturing of such devices. Different approaches like additives, antisolvents, composition engineering, and different deposition techniques have been employed to improve the morphology of the perovskite films. Additives that can form Lewis acid-base adducts are known to minimize extrinsic impacts that trigger defects in ambient air. In this work, we used the 3-thiophenemalonic acid (3-TMA) additive, which possesses thiol and carboxyl functional groups, to convert PbI2, PbCl2, and CH3NH3I to CH3NH3PbI3 completely. This strategy is effective in regulating the kinetics of crystallization and improving the crystallinity of the light-absorbing layer under high relative humidity (RH) conditions (30-50%). As a result, the 3-TMA additive increases the yield of the power conversion efficiency (PCE) from 14.9 to 16.5% and its stability under the maximum power point. Finally, we found that the results of this work are highly relevant and provide additional inputs to the ongoing research progress related to additive engineering as one of the efficient strategies to reduce parasitic recombination and enhance the stability of inverted OIHPSCs in ambient environment processing.

High-throughput calculation for the screening of formamidinium halide perovskite for solar cells.

128 organic halide perovskites are systematically investigated using high-throughput first principles calculations where Ge and Sn-based materials are searched. The results revealed that all calculated materials exhibited exothermic reactions. Notably, a correlation between the heat of formation and X-site ions is identified. Six specific compounds, namely FA-Ge-I-I-I, FA-Sn-F-I-I, FA-Sn-Cl-I-I, FA-Sn-Br-Br-I, FA-Sn-Br-I-I, and FA-Sn-I-I-I, where FA stands for formamidinium, are found to have a bandgap ranging from 1.0 to 2.0 eV, characterized by a direct bandgap in their band structure. Electronic structure analysis indicated that the CBM (conduction band minimum) is influenced by the B-site p-orbital, while the VBM (valence band maximum) is influenced by the X-site p-orbitals. This study underscores the capability of high-throughput calculations to unveil hidden trends in perovskite materials, offering an effective approach for the exploration of promising perovskite materials.

An open-cage bis[60]fulleroid as an electron transport material for tin halide perovskite solar cells.

An open-cage bis[60]fulleroid (OC) was applied as an electron transport material (ETM) in tin (Sn) halide perovskite solar cells (PSCs). Due to the reduced offset between the energy levels of Sn-based perovskites and ETMs, the power conversion efficiency (PCE) of Sn-based PSCs with OC reached 9.6% with an open-circuit voltage (VOC) of 0.72 V. Additionally, OC exhibited superior thermal stability and provided 75% of the material without decomposition after vacuum deposition. The PSC using vacuum-deposited OC as the ETM could afford a PCE of 7.6%, which is a big leap forward compared with previous results using vacuum-deposited fullerene derivatives as ETMs.