Stable Perovskite Solar Cells Research Articles

Enhancing efficiency and stability of inverted perovskite solar cells through synergistic suppression of multiple defects via poly(ionic liquid)-buried interface modification

The stability of perovskite solar cells (PSCs) is adversely affected by nonradiative recombination resulting from buried interface defects. Herein, we synthesize a polyionic liquid, poly(p-vinylbenzyl trimethylammonium hexafluorophosphate) (PTA), and introduce it into the buried interface of PSCs. The quaternary ammonium cation (N(–CH3)3+) in PTA can fill the vacancies of organic cations within the perovskite structure and reduce shallow energy level defects. Additionally, the hexafluorophosphate (PF6−) in PTA forms a Lewis acid-base interaction with Pb2+ in the perovskite layer, effectively passivating deep energy level defects. Furthermore, hydrogen bonding can be established between organic cations and the PF6− anion, preventing the formation of shallow energy level defects. Through this synergistic mechanism, the deep and shallow energy level defects are effectively mitigated, resulting in improved device performance. As a result, the resulting treated inverted PSC exhibits an impressive power conversion efficiency (PCE) of 24.72 %. Notably, the PTA-treated PSCs exhibit remarkable stability, with 88.5 % of the original PCE retained after undergoing heat aging at 85 °C for 1078 h, and 89.1 % of the initial PCE maintained following continuous exposure to light for 1100 h at the maximum power point. Synergistically suppressing multiple defects at the buried interface through the use of polyionic liquids is a promising way to improve the commercial viability of PSCs.

Thiocarbonyl-Based Hole Transport Materials with Enhanced Defect Passivation Ability for Efficient and Stable Perovskite Solar Cells.

Organic hole transporting materials (HTMs) are extensively studied in perovskite solar cells (PSCs). The HTMs directly contact the underlying perovskite material, and they play additional roles apart from hole transporting. Developing organic HTMs with defect passivation function has been proved to be an efficient strategy to construct efficient and stable PSCs. In this work, new organic molecules with thiocarbonyl (C═S) and carbonyl (C═O) functional groups are synthesized and applied as HTMs (named FN-S and FN-O). FN-S with C═S can be facilely obtained from FN-O containing C═O. Notably, the C═S in FN-S results in superior defect passivation ability compared to FN-O. Moreover, FN-S exhibits excellent hole extraction/transport capability. Conventional PSCs using FN-S as HTM show an impressive power conversion efficiency (PCE) of 23.25%, with excellent long-term stability and operational stability. This work indicates that simply converting C═O to C═S is an efficient way to improve the device performance by strengthening the defect passivation functionality.

Understanding of Defect Passivation Effect on Wide Band Gap p-i-n Perovskite Solar Cell.

The wide band gap perovskite solar cells (PSCs) have attracted considerable attention for their great potential as top cells in high efficiency tandem cell application. However, the photovoltaic performance and stability of PSCs are constrained by nonradiative recombination, primarily stemming from defects within the bulk and at the interface of charge transport layer/perovskite and phase segregation. In this study, we systematically investigated the effects of 2-thiopheneethylammonium chloride (TEACl) on a wide band gap (∼1.67 eV) Cs0.15FA0.65MA0.20Pb(I0.8Br0.2)3 (CsFAMA) perovskite solar cell. TEACl was employed as a passivation layer between the perovskite and electron transport layer (ETL). With TEACl treatment, charged defects responsible for sub-band absorption and electrostatic potential fluctuation were effectively suppressed by the passivation of bulk defects. The incorporation of TEACl, which led to the formation of a TEA2PbX4/Perovskite (2D/3D) heterojunction, facilitated better band alignment and effective passivation of interface defects at the ETL/CsFAMA. Owing to these beneficial effects, the TEACl passivated PSC achieved a photo conversion efficiency (PCE) of 19.70% and retained ∼85% of initial PCE over ∼1900 h, surpassing the performance of the untreated PSC, which exhibited a PCE of 16.69% and retained only ∼37% of its initial PCE.

Governing the dispersion of quasi-2D perovskite phases toward efficient and stable perovskite solar cells

Governing the dispersion of quasi-2D perovskite phases toward efficient and stable perovskite solar cells

Non-Fullerene Organic Electron Transport Materials toward Stable and Efficient Inverted Perovskite Photovoltaics.

Inverted perovskite solar cells (PSCs) attract continuing interest due to their low processing temperature, suppressed hysteresis, and compatibility with tandem cells. Considerable progress has been made with reported power conversion efficiency (PCE) surpassing 26%. Electron transport Materials (ETMs) play a critical role in achieving high-performance PSCs because they not only govern electron extraction and transport from the perovskite layer to the cathode, but also protect the perovskite from contact with ambient environment. On the other hand, the non-radiative recombination losses at the perovskite/ETM interface also limits the future development of PSCs. Compared with fullerene derivatives, non-fullerene n-type organic semiconductors feature advantages like molecular structure diversity, adjustable energy level, and easy modification. Herein, the non-fullerene ETM is systematically summarized based on the molecular functionalization strategy. Various types of molecular design approaches for producing non-fullerene ETM are presented, and the insight on relationship of chemical structure and device performance is discussed. Meantime, the future trend of non-fullerene ETM is analyzed. It is hoped that this review provides insightful perspective for the innovation of new non-fullerene ETMs toward more efficient and stable PSCs.

Ionic liquid gel microspheres as multifunctional bi-component additives for the crystallinity manipulation and defect passivation in all-air-processed perovskite solar cells

Additives have played a critical role in enhancing the efficiency and stability of perovskite solar cells (PSCs). At present, most of the effective additives are composed of one component, with little attention being given to the potential of bi-component. Herein, we report a novel synergistic strategy to construct ionic liquid gel microspheres (ILG-microspheres) as multifunctional bi-component additives by emulsion polymerization. The synergistic effect of polymeric methyl methacrylate and 1-butyl-3-methylimidazole hexafluorophosphate (BMIMPF6) can effectively improve perovskite crystallization quality and passivated GBs. As a result, an all-air-processed champion device with ILG-microsphere exhibits a power conversion efficiency of 22.31 % with a Voc of 1.206 V. Moreover, the long-term stability of optimized PSC remains 86.5 % of initial efficiency after being stored in the air atmosphere for 1500 h, and its thermal stability is also enhanced. This exploitation of ILG-microsphere as multifunctional bi-component additives provides a promising strategy for the development of all-air-processed high-performance PSCs.

Synergistic defect passivation and strain compensation toward efficient and stable perovskite solar cells

Rational interface engineering is essential for minimizing interfacial nonradiative recombination losses and enhancing device performance. Herein, we report the use of bidentate diphenoxybenzene (DPOB) isomers as surface modifiers for perovskite films. The DPOB molecules, which contain two oxygen (O) atoms, chemically bond with undercoordinated Pb2+ on the surface of perovskite films, resulting in compression of the perovskite lattice. This chemical interaction, along with physical regulations, leads to the formation of high-quality perovskite films with compressive strain and fewer defects. This compressive strain-induced band bending promotes hole extraction and transport, while inhibiting charge recombination at the interfaces. Furthermore, the addition of DPOB will reduce the zero-dimensional (0D) Cs4PbBr6 phase and produce the two-dimensional (2D) CsPb2Br5 phase, which is also conducive to the improvement of device performance. Ultimately, the resulting perovskite films, which are strain-released and defect-passivated, exhibit exceptional device efficiency, reaching 10.87% for carbon-based CsPbBr3 device, 14.86% for carbon-based CsPbI2Br device, 22.02% for FA0.97Cs0.03PbI3 device, respectively. Moreover, the unencapsulated CsPbBr3 PSC exhibits excellent stability under persistent exposure to humidity (80%) and heat (80 °C) for over 50 days.

Molecular Interlayer with Large Cations Supports Efficient, Stable Perovskite Solar Cells

Molecular Interlayer with Large Cations Supports Efficient, Stable Perovskite Solar Cells

Synthesis and stability of Cs-rich α phase Cs1-xDMAxPbI2Br(0 ≤ x ≤ 0.3) perovskite film

In this study, we successfully synthesized α-phase Cs1-xDMAxPbI2Br(0 ≤ x ≤ 0.3) without impurity and conducted device performance research and stability testing on it. The champion photoelectric conversion efficiency of α phase Cs0.8DMA0.2PbI2Br in inverted perovskite solar cells is 8.24 %. Compared with pure CsPbI2Br without DMA+, humidity stability of α-Cs0.8DMA0.2PbI2Br has been improved and it also maintains thermal and ultraviolet stability. This strategy shows bright application prospect for improving the stability of CsPbI2Br perovskite solar cells.

Surface modification of SnO2 electron transporting layer by graphene quantum dots for performance and stability improvement of perovskite solar cells

The surface modification of SnO2 electron transporting layer (ETL) is investigated for the performance and stability improvement of perovskite solar cells by adding citric acid (SnO2-citric) and graphene quantum dots (SnO2-GQDs) in SnO2 ETL precursors for carboxyl group and GQDs, respectively. As a result, the hydrophobic surface of SnO2-GQDs is obtained by adding GQDs to the SnO2 precursor, forming SnO2-GQDs ETL. In addition, the hydrophobic surface of SnO2 ETL is significant in increasing grain size crystallinity of perovskite obtained by this modification process. Also, the charge trap density and recombination carriers between ETL and perovskite interface were advanced. Thus, the surface modification of SnO2-GQDs ETL can enhance the power conversion efficiency (PCE) of PSCs at the highest value of 17.81% from 15.52% with a decrease of the hysteresis effect. The enhancement is due to the combining effect of carboxyl groups and GQDs interface engineering between ETL and perovskites layers. Also, the stability of perovskite solar cells without encapsulation for 28 days is achieved. These suggest that the combining effect can be used in surface modification and for efficiency enhancement of PSCs.

PhDMADBr assisted additive or interface engineering for efficient and stable perovskite solar cells fabricated in ambient air

The fabrication of high-quality perovskite films with low defect density in ambient air is an important approach to enhance the power conversion efficiency (PCE) and stability of perovskite solar cells (PSCs). In this paper, efficient and stable PSCs were fabricated in ambient air, and p-xylilenediamine bromide (PhDMADBr) assisted additive or interface engineering were carried out to modify perovskite films, which was dispersed into the electron transport layer (ETL) or deposited in the ETL/ perovskite interface. Notably, interaction between PhDMADBr and perovskite layer could reduce defect density and release residual stress of the active layer, which would induce a high-quality perovskite film, and accelerate the transport rate and prolong lifetimes of charge carriers, contributing to the PCE and stability of devices. As a result, compared with the PCE of the control device (22.54 %), the PhDMADBr modified target PSCs exhibited the enhanced PCE of 24.15 % and 23.74 % after additive or interface treatments in ambient air, respectively. Except the improvement of the PCE, PhDMADBr-based devices also presented the enhanced moisture stability. The average efficiency retained the 88 % or 84 % of initial efficiency after 120 h with RH of 40 ± 5 % for additive or interface modification, respectively. In contrast, the PCE of the control devices would decline to 51 % of initial efficiency after storage for 120 h.

Defect Engineering at Buried Interface of Perovskite Solar Cells.

Perovskite solar cells (PSC) have developed rapidly since the past decade with the aim to produce highly efficient photovoltaic technology at a low cost. Recently, physical and chemical defects at the buried interface of PSC including vacancies, impurities, lattice strain, and voids are identified as the next formidable hurdle to the further advancement of the performance of devices. The presence of these defects has unfavorably impacted many optoelectronic properties in the PSC, such as band alignment, charge extraction/recombination dynamics, ion migration behavior, and hydrophobicity. Herein, a broad but critical discussion on various essential aspects related to defects at the buried interface is provided. In particular, the defects existing at the surface of the underlying charge transporting layer (CTL) and the bottom surface of the perovskite film are initially elaborated. In situ and ex situ characterization approaches adopted to unveil hidden defects are elucidated to determine their influence on the efficiency, operational stability, and photocurrent-voltage hysteresis of PSC. A myriad of innovative strategies including defect management in CTL, the introduction of passivation materials, strain engineering, and morphological control used to address defects are also systematically elucidated to catalyze the further development of more efficient, reliable, and commercially viable photovoltaic devices.

Application of biodegradable poly(lactide-co-glycolide) (PLGA) for efficient & stable perovskite solar cells

Since numerous defects can deteriorate the efficiency as well as long-term stability of perovskite solar cells (PSCs), it is important to control the defects for the industrialization of PSCs. Among various defects, interest is mainly focused on treating the uncoordinated Pb2+, which not only causes the lower performance of PSCs, but also is considered as a risk to the environment and human. Herein, we investigate a FDA (Food and Drug Administration) approved biodegradable poly(lactide-co-glycolide) (PLGA) as a polymer additive to passivate uncoordinated Pb2+. PLGA contains carbonyl groups (CO), which can strongly form a coordination bonding with Pb2+, resulting in the reduction of non-radiative charge recombination and improvement of charge carrier movement. Therefore, the power conversion efficiency (PCE) of air-processed PSCs enhances from 15.87 % to 17.09 %, especially the fill factor enhances from 77.19 % to 81.33 %. The PLGA passivated devices exhibit superior thermal stability maintaining 70 % of the initial PCE for ∼100 h in the air conditions without any encapsulation, moreover, in the test of Pb leakage from perovskite, restricted dissolving of Pb in water was confirmed as a result of immobilization of uncoordinated Pb2+ ion by PLGA.

Indium Tin Oxide Induced Internal Positive Feedback and Indium Ion Transport in Perovskite Solar Cells.

Stability is the most pressing challenge hindering the commercialization of perovskite solar cells (PSCs), and previous efforts focused more on enhancing the resistance of PSCs to external stimulus. Here, we found that the indium tin oxide (ITO) will deteriorate the photovoltaic performance of PSCs through positive feedback cycles. Specifically, the perovskite degradation products will cross the electron transport layer to chemically etch the electrode ITO to generate In3+, which will migrate upwards into the perovskite film. Then, the reaction that corrodes ITO consumes the decomposition products of perovskite and shifts the balance of the perovskite decomposition reaction, further promoting the degradation and thus falling into a positive feedback cycle. Moreover, the In3+ in the perovskite film was found to accumulate at the upper surface, which would lead to n-type doping of perovskite film to form the energy barrier for interface carrier extraction. Subsequently, the chelating molecule ethylenediaminetetraacetic acid disodium salt (EDTA-2Na) was introduced onto ITO to firmly chelate the In3+ and prevent it from migrating upward, thus breaking this internal positive feedback cycle and significantly enhancing the efficiency and stability of PSCs. This work provides new perspectives for understanding the mechanism of photovoltaic performance loss and ionic transport in PSCs.

Indium Tin Oxide Induced Internal Positive Feedback and Indium Ion Transport in Perovskite Solar Cells

AbstractStability is the most pressing challenge hindering the commercialization of perovskite solar cells (PSCs), and previous efforts focused more on enhancing the resistance of PSCs to external stimulus. Here, we found that the indium tin oxide (ITO) will deteriorate the photovoltaic performance of PSCs through positive feedback cycles. Specifically, the perovskite degradation products will cross the electron transport layer to chemically etch the electrode ITO to generate In3+, which will migrate upwards into the perovskite film. Then, the reaction that corrodes ITO consumes the decomposition products of perovskite and shifts the balance of the perovskite decomposition reaction, further promoting the degradation and thus falling into a positive feedback cycle. Moreover, the In3+ in the perovskite film was found to accumulate at the upper surface, which would lead to n‐type doping of perovskite film to form the energy barrier for interface carrier extraction. Subsequently, the chelating molecule ethylenediaminetetraacetic acid disodium salt (EDTA‐2Na) was introduced onto ITO to firmly chelate the In3+ and prevent it from migrating upward, thus breaking this internal positive feedback cycle and significantly enhancing the efficiency and stability of PSCs. This work provides new perspectives for understanding the mechanism of photovoltaic performance loss and ionic transport in PSCs.

Non-destructive buffer enabling near-infrared-transparent inverted inorganic perovskite solar cells toward 1400 h light-soaking stable perovskite/Cu(In,Ga)Se2 tandem solar cells

Near-infrared (NIR) transparent inverted all-inorganic perovskite solar cells (PSCs) are excellent top cell candidates in tandem applications. An essential challenge is the replacement of metal contacts with transparent conductive oxide (TCO) electrodes, which requires the introduction of a buffer layer to prevent sputtering damage. In this study, we show that the conventional buffers (i.e., small organic molecules and atomic layer deposited metal oxides) used for organic-inorganic hybrid perovskites are not applicable to all-inorganic perovskites, due to non-uniform coverage of the vulnerable layers underneath, deterioration upon ion bombardment and moisture induced perovskite phase transition. A thin film of metal oxide nanoparticles by the spin-coating method serves as a non-destructive buffer layer for inorganic PSCs. All-inorganic inverted near-infrared-transparent PSCs deliver a PCE of 17.46% and an average transmittance of 73.7% between 780 and 1200 nm. In combination with an 18.56% Cu(In,Ga)Se2 bottom cell, we further demonstrate the first all-inorganic perovskite/CIGS 4-T tandem solar cell with a PCE of 24.75%, which exhibits excellent illumination stability by maintaining 86.7% of its initial efficiency after 1400 h. The non-destructive buffer lays the foundation for efficient and stable NIR-transparent inverted inorganic perovskite solar cells and perovskite-based tandems.

Chelating Dual Interface for Efficient and Stable Crystal Growth and Iodine Defect Management in Sn-Pb Perovskite Solar Cells.

Suppressing Sn2+ oxidation and rationally controlling the crystallization process of tin-lead perovskite (Sn-Pb PVK) films by suitable bonding methods have emerged as key approaches to achieving efficient and stable Sn-Pb perovskite solar cells (PSCs). Herein, the chelating coordination is performed at the top and bottom interfaces of Sn-Pb PVK films. The chelation strength is stronger toward Sn2+ than Pb2+ by introducing oligomeric proanthocyanidins (OPC) at the bottom interface. This difference in chelation strength resulted in a spontaneous gradient distribution of Sn/Pb within the perovskite layer during crystallization, particularly enhancing the enrichment of Sn2+ at the bottom interface and facilitating the extraction and separation of photogenerated charge carriers in PSCs. Simultaneously, this top-down distribution of gradually increasing Sn content slowed down the crystallization rate of Sn-Pb PVK films, forming higher-quality films. On the top interface of the PVK, trifluoroacetamidine (TFA) was used to inhibit the generation of iodine vacancies (VI) through chelating with surface-uncoordinated Pb2+/Sn2+, further passivating defects while suppressing the oxidation of Sn2+. Ultimately, the PSCs with simultaneous chelation at both top and bottom interfaces achieved a power conversion efficiency (PCE) of 23.31% and an open-circuit voltage (VOC) exceeding 0.90 V. The stability of unencapsulated target devices in different environments also improved.

Interaction of C60 with Methylammonium Lead Iodide Perovskite Surfaces: Unveiling the Role of C60 in Surface Engineering.

Understanding the interaction between fullerene (C60) and perovskite surfaces is pivotal for advancing the efficiency and stability of perovskite solar cells. In this study, we investigate the adsorption behavior of C60 on methylammonium lead iodide (MAPbI3) surfaces using periodic density functional theory calculations. We explore various surface terminations and defect configurations to elucidate the influence of surface morphology on the C60-perovskite interaction, computing the adsorption energy and transfer of charge. Our results reveal distinct adsorption energies and charge transfer mechanisms for different surface terminations, shedding light on the role of surface defects in modifying the electronic structure and stability of perovskite materials. Furthermore, we provide insights into the potential of C60 to passivate surface defects, playing a relevant role in the surface reconstruction after the formation of defects. This comprehensive understanding of C60-perovskite interactions offers valuable guidelines about the role of fullerenes on surface structure and reconstruction.

Inhibiting perovskite decomposition by a creeper-inspired strategy enables efficient and stable perovskite solar cells

The commercialization of perovskite solar cells is badly limited by stability, an issue determined mainly by perovskite. Herein, inspired by a natural creeper that can cover the walls through suckers, we adopt polyhexamethyleneguanidine hydrochloride as a molecular creeper on perovskite to inhibit its decomposition starting from the annealing process. The molecule possesses a long-line molecular structure where the guanidinium groups can serve as suckers that strongly anchor cations through multiple hydrogen bonds. These features make the molecular creeper can cover perovskite grains and inhibit perovskite decomposition by suppressing cations’ escape. The resulting planar perovskite solar cells achieve an efficiency of 25.42% (certificated 25.36%). Moreover, the perovskite film and device exhibit enhanced stability even under harsh damp-heat conditions. The devices can maintain >96% of their initial efficiency after 1300 hours of operation under 1-sun illumination and 1000 hours of storage under 85% RH, respectively.

Stable and Lead-Safe Polyphenol-Encapsulated Perovskite Solar Cells.

Lead (Pb) halide perovskite solar cells (PSCs) exhibit impressive power conversion efficiencies close to those of their silicon counterparts. However, they suffer from moisture instability and Pb safety concerns. Previous studies have endeavoured to address these issues independently, yielding minimal advancements. Here, a general nanoencapsulation platform using natural polyphenols is reported for Pb-halide PSCs that simultaneously addresses both challenges. The polyphenol-based encapsulant is solution-processable, inexpensive (≈1.6 USDm-2), and requires only 5min for the entire process, highlighting its potential scalability. The encapsulated devices with a power conversion efficiency of 20.7% retained up to 80% of their peak performance for 2000h and up to 70% for 7000h. Under simulated rainfall conditions, the encapsulant rich in catechol groups captures the Pb ions released from the degraded perovskites via coordination, keeping the Pb levels within the safe drinking water threshold of 15ppb.