High-efficiency Perovskite Solar Cells Research Articles

Anion exchange strategies in radical doped hole transporting material for high-efficiency perovskite solar cells

Perovskite solar cells (PSCs) have received significant attention due to their superior photovoltaic conversion capability. To date, most efficient PSCs use p-doped organic semiconductors as hole-transporting layers (HTL). Many evidences show that the generally used p-doping system, i.e. lithium bis(trifluoromethane)sulfonimide and air exposure threaten the reproducibility and stability of PSCs. Recently, free radicals doped HTL have been used to fabricate efficient PSCs without using anying harmful dopants. Herein, we found that the low doping efficiency of radials is due to a weak Madelung potential. We developed a spontaneous anion exchange to stabilize the radical doped HTL via introducing an additional anion into the host-guest system. Conductivity and interfacial charge transfer are significantly enhanced by regulating the size of anions. We found that the conductivity and device performance is increased when the size of the anion increases. As a result, a champion efficiency of 20.7% under AM 1.5G 1-sun irradiation is achieved, which is comparable with the conventionally doped HTL. Moreover, the solar cells showed significantly enhanced stability against the humidity stress, which we attribute to the use of HTLs devoid of environmental sensitive additives.

Multifunctional Interface Treatment of Phosphate for High-Efficiency Perovskite Solar Cells

Multifunctional Interface Treatment of Phosphate for High-Efficiency Perovskite Solar Cells

Comparative study of 2D/3D hybrid perovskite solar cell containing different modified carbon nanomaterials based Electron Transport Layers (ETL)

Charge transport facilitation in the electron transport layer is necessary for high-efficiency perovskite solar cells. Carbonaceous materials such as graphene (G) and carbon nanotubes (CNTs) have been extensively used in energy storage and conversion applications. Here we report the novel design of ETL based on the combinations of tin oxide, graphene nanoribbons, nitrogen-doped graphene nanoribbons, and gold nanoparticles for 2D/3D perovskite solar cells. Three different ETLs were employed to get three 2D/3D PSCs with novel device architectures. The effect of different ETLs on the performance of solar cells is investigated. Results reveal that due to better optical and electrical behavior, the solar cell employing a composite of tin oxide, graphene nanoribbons, nitrogen-doped graphene nanoribbons, and gold nanoparticles as ETL has attained a higher PCE of 10.77%.

Rubidium fluoride additive for high-efficiency and low-hysteresis all-inorganic CsPbI3 perovskite solar cells

All-inorganic CsPbI3 perovskite solar cells (PSCs) technology is gradually maturing because of its excellent photoelectric characteristics. However, the hysteresis phenomenon induced by ion migration in the perovskite film not only seriously affects the performance of the device, but also accelerates the degradation of the film, which limits the further improvement of power conversion efficiency (PCE) for CsPbI3 PSCs. Herein, in this paper, a new inorganic fluorine-containing additive rubidium fluoride (RbF) was introduced as a precursor additive. The incorporation of RbF effectively improved the crystallization kinetics of CsPbI3 perovskite film and effectively suppressed the occurrence of hysteresis. The defects on the CsPbI3 perovskite film are remarkably inhibited and the carrier dynamics process is greatly promoted with the incorporation of 0.03 mol% RbF. In addition, the non-radiative recombination is significantly suppressed, and the device stability is substantially improved. In particular, by doping 0.03 mol% RbF into the CsPbI3, the hysteresis index of PSCs decreases to 0.003. The introduction of RbF effectively improves the device performance, and the highest efficiency has reached to 17.21%. The environmental stability has also been significantly enhanced with the RbF doping.

SnO2:TiO2 hybrid nanocrystals as electron transport layer for high-efficiency and stable planar perovskite solar cells

SnO2:TiO2 hybrid nanocrystals as electron transport layer for high-efficiency and stable planar perovskite solar cells

Potassium chloride passivation for sputtered SnO2 to eliminate hysteresis and enhance the efficiency of perovskite solar cells

In perovskite solar cells (PSCs), tin oxide (SnO2) has been widely used as the electron transport layer (ETL) due to its wide bandgap and high electron mobility. Among the various deposition methods, radio frequency (RF) sputtering offers many advantages for the commercialization of PSCs fabrication. However, conventional PSCs with sputtered SnO2 are subject to severe hysteresis, which occurs owing to defect sites at the ETL-perovskite interface. Further, these defect sites induce non-radiative carrier recombination, causing a decrease in open-circuit voltage and device fill factor. Herein, the surface of RF-sputtered SnO2 was passivated with potassium chloride (KCl) aqueous solution. Through this treatment, it was possible to passivate the defect sites at the interface and change the band alignment for effective electron transport. Thus, a decrease in the trap density of the perovskite led to an increase in efficiency (from 20.9% to 21.9%) and reduction in the hysteresis (from 10.5% to 2.7%) of the PSC. Hence, the KCl passivation process of RF-sputtered SnO2 could be adopted to manufacture hysteresis-free high-efficiency PSCs.

Ladder-type dihydronaphtho[1,2,3,4-rst]pentaphene as building block to construct hole-transporting materials for perovskite solar cells

The stability and photovoltaic performance of perovskite solar cells (PSCs) are greatly affected by the use of hole-transporting materials (HTMs). Polycyclic aromatic hydrocarbons (PAHs) are known for their planar structures, which facilitate efficient charge transport and intermolecular interactions, resulting they possess unique electronic and optical properties. In this study, we describe the synthesis of three D‒π‒D type PAHs-based HTMs compounds (DC-1, DC-2, and DC-3) that contain dihydronaphtho[1,2,3,4-rst]pentaphene (DHNP) as a π conjugation bridge, p-methoxy group-substituted arylamine, and diphenylamine-substituted carbazole groups as the donor groups. These DHNP-based molecules can be used as hole-transporting materials in PSCs due to their favorable frontier molecular orbitals (HOMO/LUMO) energy levels. The PSC devices fabricated with DC-1 yielded a highly efficient power conversion efficiency (PCE) of 18.09%, outperforming those based on DC-2 (13.21%) and DC-3 (14.91%), and slightly higher than those using control spiro-OMeTAD (16.93%). The proposed novel D‒π‒D molecules demonstrate potential as HTMs with promising performance for PSCs and contribute to the development of high-efficiency perovskite solar cells.

Printable High-efficiency and Stable FAPbBr3 Perovskite Solar Cells for Multifunctional Building-integrated Photovoltaics.

Perovskite solar cells (PSCs) show great promise for next-generation building-integrated photovoltaic (BIPV) applications because of their abundance of raw materials, adjustable transparency, and cost-effective printable processing. Owing to the complex perovskite nucleation and growth control, the fabrication of large-area perovskite films for high-performance printed PSCs is still under active investigation. Herein, wepropose an intermediate-phase-transition-assisted one-step blade coating for an intrinsic transparent formamidinium lead bromide (FAPbBr3 ) perovskite film. The intermediate complex optimized the crystal growth path of FAPbBr3 , resulting in a large-area, homogeneous, and dense absorber film. A champion efficiency of 10.86% with high open-circuit voltage up to 1.57V wasobtained with a simplified device architecture of glass/FTO/SnO2 /FAPbBr3 /carbon. Moreover, the unencapsulated devices maintained 90% of their initial power conversion efficiency after aging at 75°C for 1000h in ambient air, and 96% after maximum power point tracking for 500h. The printed semitransparent PSCs, with average visible light transmittance over 45%, demonstrated high efficiencies for both small devices (8.6%) and 10 × 10 cm2 modules (5.55%). Finally, the ability to customize the color, transparency, and thermal insulation properties of FAPbBr3 PSCs makes them high prospects as multifunctional BIPVs. This article is protected by copyright. All rights reserved.

Designing of dimethylfluorene-based hole transport materials for high-performance organic/perovskite solar cells

In this study, we present the design of five new hole-transporting materials (ZM1, ZM2, ZM3, ZM4, and ZM5) based on dimethylfluorene through end-capped acceptors via thiophene linkers. We aimed to enhance the photovoltaic properties of hole-transporting materials (HTMs) for potential use in high-efficiency perovskite solar cells (PSCs). We employed density functional theory (DFT) based calculations to investigate the electronic and photovoltaic properties of the designed HTMs. Our results demonstrated that designed HTMs possess superior planarity, deeper HOMOs energies, and high solubility with small energy band gap (Eg) compared to the reference (ZR) and Spiro-OMeTAD HTMs, leading hole extraction and efficacious solution processing properties. This effectively drives the transport of holes from the perovskite layer with high open-circuit voltages (1.15 V to 1.25 V). The results of the hole charge transfer integral of the designed HTMs (0.244 eV to 0.346 eV) indicate their improved hole mobility rate for PSCs. Additionally, all designed HTMs exhibited superior anticipated power conversion efficiency (25.87% to 28.33%) with a higher fill factor (0.8948 to 0.9014) compared to the reference molecule (13.22%). Our findings suggested that ZM1-ZM5 molecules are advantageous HTMs for the fabrication of high-performance PSCs, which may have the potential for future commercial use in the solar industry.

Stable and High-Efficiency Perovskite Solar Cells Using Effective Additive Ytterbium Fluoride.

With better light utilization, larger tolerance factor, and higher power conversion efficiency (PCE), the HC(NH2 )2 + (FA)-based perovskite is proven superior to the popular CH3 NH3 + (MA)- and Cs-based halide perovskites in solar cell applications. Unfortunately, limited by intrinsic defects within the FA-based perovskite films, the perovskite films can be easily transformed into a yellow δ-phase at room temperature in the fabrication process, a troublesome challenge for its further development. Here, ytterbium fluoride (YbF3 ) is introduced into the perovskite precursor for three objectives. First of all, the partial substitution of Yb3+ for Pb2+ in the perovskite lattice increases the tolerance factor of the perovskite lattice and facilitates the formation of the α phase. Second, YbF3 and DMSO in the solvent form a Lewis acid complex YbF3 ·DMSO, which can passivate the perovskite film, reduce defects, and improve device stability. Consequently, the YbF3 modified Perovskite solar cell exhibits a champion conversion efficiency of 24.53% and still maintains 90% of its initial efficiency after 60 days of air exposure under 30% relative humidity.

A Binary Solution Strategy Enables High-Efficiency Quasi-2D Perovskite Solar Cells with Excellent Thermal Stability.

Quasi-two-dimensional (2D) perovskites are highly promising light-harvesting materials for commercialization of perovskite solar cells (PSCs) owing to the excellent materials stability. However, the coexistence of multiple n-value species in 2D perovskites often causes increased complexities in crystallization that can negatively affect the eventual photovoltaic performance. Herein, we present a binary solution based strategy via introducing nontoxic and widely accessible CH3COOH (HAc) as a co-solvent for preparing high-quality 2D perovskite films. Based on a 2D perovskite model system, (AA)2MA4Pb5I16 (n = 5), we show that the prenucleation and grain growth kinetics are appreciably modified with HAc, which benefits from the strong electron-donating ability of HAc with the key component of PbI2, leading to formation of favorable cluster aggregates and resultant modulation of crystal growth. With the HAc-based method, the devices yield a boosted photovoltaic efficiency of 18.55% with an impressive photovoltage of 1.26 V. The champion cells exhibit a supreme thermal stability, showing <3% efficiency degradation under continuous thermal aging for 800 h.

Visualizing Interfacial Energy Offset and Defects in Efficient 2D/3D Heterojunction Perovskite Solar Cells and Modules.

Currently, the full potential of perovskite solar cells (PSCs) is limited by chargecarrier recombination owing to imperfect passivation methods. Here, the recombination loss mechanisms owing to the interfacial energy offset and defects are quantified. The results show that a favorable energy offset can reduce minority carriers and suppress interfacial recombination losses more effectively than chemical passivation. To obtain high-efficiency PSCs, 2D perovskites are promising candidates, which offer powerful field effects and require only modest chemical passivation at the interface. The enhanced passivation and charge-carrier extraction offered by the 2D/3D heterojunction PSCs has boosted their power conversion efficiency to 25.32% (certified 25.04%) for small-size devices and to 21.48% for a large-area module (with a designated area of 29.0cm2 ). Ion migration is also suppressed by the 2D/3D heterojunction, such that the unencapsulated small-size devices maintain 90% of their initial efficiency after 2000h of continuous operation at the maximum power point.

Reduction-Active Antisolvent: A Universal and Innovative Strategy of Further Ameliorating Additive Optimization for High Efficiency Perovskite Solar Cells.

To further ameliorate current additive engineering of perovskites for viable applications, the inherent limitations should be overcome; these include weakened coordination of the dopants to the [PbI6]4- octahedra during crystallization and ubiquity of ineffective bonding sites. Herein, we introduce a facile strategy for synthesizing a reduction-active antisolvent. Washing with reduction-active PEDOT:PSS-blended antisolvent substantially enhances the intrinsic polarity of the Lewis acid (Pb2+) in [PbI6]4- octahedra, which causes significant strengthening of the coordinate bonding between additives and perovskite. Thus, coordination of the additive to the perovskite becomes much stable. Additionally, the enhanced coordination ability of Pb2+ can enhance the effective bonding sites and further enhance the efficacy of additive optimization to the perovskite. Here, we demonstrate five different additives as dopant bases and repeatedly verify the universality of this approach. The photovoltaic performance and stability of doped-MAPbI3 devices are further improved, revealing the advanced potential of additive engineering.

Eco-friendly glucose assisted structurally simplified high-efficiency tin-lead mixed perovskite solar cells

Achieving highly-efficient and stable perovskite solar cells (PSCs) with a simplified structure remains challenging, despite the tremendous potential for reducing preparation cost and facile processability by removing hole transport layer (HTL). In this work, eco-friendly glucose (Gl) as an interface modifier for HTL-free narrow bandgap tin-lead (Sn-Pb) PSCs is proposed. Gl not only enhances the wettability of the indium tin oxide to promote perovskite heterogeneous nucleation on substrate, but also realizes defect passivation by interacting with uncoordinated Pb2+ and Sn2+ in perovskite films. As a result, the quality of the perovskite films has been significantly improved, accompanied by reduced defects of bottom interface and optimized energy level structure of device, leading to an efficiency increase and a less nonradiative voltage loss of 0.102 V (for a bandgap of ∼1.26 eV). Consequently, the optimized PSC delivers an unprecedented efficiency over 21% with high open-circuit voltage and enhanced stability, outperforming the control device. This work demonstrates a cost-effective approach to develop simplified structure high efficiency HTL-free Sn-Pb PSC.

Heterocyclic Functionalized Donor-Acceptor Hole-Transporting Materials for Inverted Perovskite Solar Cells.

Hole transport materials (HTMs) with appropriate energy levels and comprehensive passivation effects help to obtain highly efficient and stable perovskite solar cells (PSCs). Electron-deficient character-induced HTMs can generate varying energy level alignments near the HTM/perovskite interface. Herein, we report the synthesis and investigation of two new dipolar HTMs, WWC103 and WWC105, based on 2-(1,1-dicyanomethylene)rhodamine and 4-cynophenylacetonitrile acceptors, enabling high-efficiency mixed-cation mixed-halide perovskite solar cells. Apart from having different acceptors, these HTMs are built on a heterocyclic frame, which can provide passivation effects and improve the morphology of the perovskite layer. As a result, these dopant-free HTM-based solar cells show a high open-circuit voltage and good power conversion efficiency. Among both, the solar cell based on the HTM with 2-(1,1-dicyanomethylene)rhodamine exhibits a high open-circuit voltage of 1.09 V with a champion power conversion efficiency of over 20.51%. The improved performance of WWC103 over WWC105 (19.74%) is attributed to the new acceptor, which, in addition to providing good energy-level alignments and hole mobility, also holds the ability to passivate the defects. The findings suggest a new acceptor unit for constructing dopant-free HTMs for efficient PSCs.

Design and analysis of high-efficiency perovskite solar cell using the controllable photonic structure and plasmonic nanoparticles

Device modeling of CH3NH3PbI3 based controllable photonic structure and plasmonic nanoparticles perovskite solar cells (PSC) was performed. In recent years, light trapping (LT) and plasmonic structures in PSCs have been developed and attracted widespread attention and encouraged researchers to develop and test many architectures in this area. Also, using controllable photonic structures and plasmonic nanoparticles in PSCs significantly affect the power conversion efficiency (PCE). LT by photonic structure and also the interaction of incident light with plasmonic nanoparticles (NPs) is considered as a hopeful way to enhance the PCE of PSCs in this simulation. For accurate calculation and also considering all parameters on PSC, the present simulation is done using the finite element method (FEM). The simulation results showed that using a photonic structure significantly affects the photovoltaic result of the PSC, and the PCE reached from 15.62 % for the planar structure to 16.17 % for the photonic structure. Here, we concentrate on a significant aspect of nanostructures that minimizes light loss by optimizing and managing light to achieve high PCE for the PSC. Then we used plasmonic NPs at the top of the electron layer transfer (ETL), active layer, and hole transfer layer (HTL), and the best position to achieve the highest PCE was the top of HTL. Moreover, an additional layer as a complimentary layer (CH3NH3SnI3) was used to maximize efficiency with values of short circuit current (Jsc) 27.81 (mA/cm2), open circuit voltage (Voc) 0.949 (V), fill factor (FF) 81.77 % and PCE 21.85 %. Using these combined techniques opens horizons of improvement for the PCE of PSC.

Design of high efficiency perovskite solar cells based on inorganic and organic undoped double hole layer

The use of organic and inorganic double hole layers allows for efficient tuning of the matching of energy levels between each layer and improve the photovoltaic performance and stability of perovskite solar cells (PSCs). However, the cost of band matching for preparing perovskite cells is huge. In this paper, the effect of double hole layer on the performance of PSCs is analyzed by theoretical calculation, and an optimized structure of PSCs is proposed. The traditional Spiro-OMeTAD and MAPbI3 absorption layers are added with copper oxide (CuO) hole layers. The Solar Capacitor One-dimensional Tool (SCAPS) is used to simulate the relationship between the energy level matching of the hole layer and the photoelectric conversion efficiency (PCE) of the cell, and then the photovoltaic conversion performance is optimized accordingly. The results show a CuO hole layer with an energy gap of 1.5 can reduce the direct recombination of electron and hole pairs in the recombination layer, thereby increasing the filling factor (FF), while Spiro-OMeTAD can reduce electron recombination in the anode, thereby increasing short circuit current (Jsc). The FF and Jsc is increased simultaneously with the addition of a 200 nm CuO layer, which results in the increase of PCE from 16.82% to 21.82%. In addition, the absorption spectra and power density distributions of the two structures were calculated, and the mechanism of high absorption under different bands was explored. The effect of different material thickness and doping concentration on the photoelectric performance was studied, and the optimal parameters of the solar cell were determined, which increases the PCE by 5.95%. The cell structure proposed in this research can provide theoretical guidance for the development of such experiments and provide a novel design idea for structural optimization of PSCs.

Valine-Modified PbI2 for the Growth of Pinhole-Free Lead Halide Perovskite Thin Films by Vapor–Solid Reaction

In recent years, the efficiency of perovskite solar cells (PSCs) has rapidly increased, making PSCs commercially viable and able to compete with silicon solar cells. However, the technology for large-scale production of perovskite thin films still poses a significant challenge to the commercialization of PSCs. This is mainly because the thickness of the perovskite light-absorbing film is less than 1 μm and easily produces pinholes during large-scale production, causing serious charge recombination and reducing the efficiency of the device. As a result, the efficiencies of most large-scale PSC modules are significantly lower than those of small-size devices. Vapor-reaction technology is considered a crucial method to enhance the uniformity of perovskite thin films. However, current techniques are not yet advanced enough to deposit pinhole-free perovskite thin films on a large scale. One major challenge is that lead iodide (PbI2) precursor thin films have a tendency to develop a sheet-like structure with a loose morphology, which contributes to the formation of pinholes in the perovskite film. Additionally, uncoordinated Pb2+ could be easily generated in the PbI2 film during thermal evaporation, causing an increase in trap-states in the perovskite crystal. To address this, we developed a valine treatment process in this study to change the preferred orientation of PbI2 from a sheet-like to a particle-like aggregate and obtained compact PbI2 thin films. Meanwhile, this valine vapor treatment can significantly reduce the uncoordinated Pb2+ in PbI2 films. Based on this, we successfully prepared pinhole-free perovskite thin films using a vapor–solid reaction. Perovskite films based on these valine-treated PbI2 exhibited a reduced trap density and significantly improved PSCs’ performance, with a maximum efficiency exceeding 21%. Large-area PSC mini-modules (5 cm × 5 cm) produced from the perovskite film (30 cm × 30 cm) showed uniformly distributed power conversion efficiency values exceeding 17%, with the highest value reaching 18.78%. We believe that this facile valine vapor treatment holds great potential for the large-scale production of stable and high-efficiency PSC modules.

4-biphenylcarboxylic acid as defect passivation for high-efficient perovskite solar cells

Metal halide perovskite solar cells (PSCs) have been considered as one of the most promising candidates for clean and renewable energy sources, but the existence of the detrimental defects at the surface and grain boundaries seriously deteriorates the power conversion efficiency (PCE) and stability of PSCs. Defect passivation has been verified to efficiently enhance the PCE and stability of PSCs. Herein, a kind of 4-biphenylcarboxylic acid (4-BBC) is first utilized to passivate the perovskite film by a post-treatment strategy, finally improving the performance of PSCs. The carbonyl group of 4-BBC as Lewis base can interact with the uncoordinated Pb2+ ions to heal the I- vacancy defects, and its hydroxyl group can form hydrogen bond with I- anion of the perovskite to suppress the I- ionic migration. The hydrophobic biphenyl group of 4-BBC can also be beneficial to improve the stability of the perovskite film. As a result, the inverted PSCs with 4-BBC passivation indicate a best PCE (20.32 %) with lower hysteresis index (HI) of 0.39 % and better stability in comparison with the control PSCs (PCE = 18.71 %). The synergistic passivation of 4-BBC developed in this work offers an effective strategy for the fabrication of highly efficient and stable PSCs.

Fabrication of high-efficiency perovskite solar cells and mini-modules by expanding the processing window with KSCN additive

Perovskite solar cells (PSCs) have garnered significant attention due to their high efficiency and low cost, making them a promising contender for the future of photovoltaic (PV) technology. Stable and controllable preparation of high-efficiency PSCs is crucial for the advancement of perovskite PV technology's industrialization. Herein, we demonstrate an additive-assisted blade-coating technique that boasts a wide air knife pressure window processing, making it ideal for the scalable deposition of perovskite films. KSCN was added to the perovskite precursor to induce an extra endothermic reaction, which effectively reduced the solvent evaporation rate, broadened the processing window, and slowed down the nucleation and crystallization process of the perovskite film. Moreover, the introduction of K+ led to the suppression of the formation of metal Pb0 and iodine vacancies in the film. Therefore, the high-quality perovskite films with full coverage, larger grains, higher crystallinity, fewer defects, as well as large-scale uniformity can be obtained under variable air knife pressure. As a result, power conversion efficiencies of 20.40% for small-area (0.07 cm2) blade-coated PSCs and 17.62% for perovskite solar modules with an active area of 10.00 cm2 were achieved. The proposed blade-coating technique with a wide processing window holds great potential for the commercialization of perovskite PV technology.