Asymmetrically Substituted 10H,10'H-9,9'-Spirobi[acridine] Derivatives as Hole-Transporting Materials for Perovskite Solar Cells.

Hole-transporting materials (HTMs) based on the 10H, 10'H-9,9'-spirobi [acridine] core (BSA50 and BSA51) were synthesized, and their electronic properties were explored. Experimental and theoretical studies show that the presence of rigid 3,6-dimethoxy-9H-carbazole moieties in BSA 50 brings about improved hole mobility and higher work function compared to bis(4-methoxyphenyl)amine units in BSA51, which increase interfacial hole transportation from perovskite to HTM. As a result, perovskite solar cells (PSCs) based on BSA50 boost power conversion efficiency (PCE) to 22.65 %, and a PSC module using BSA50 HTM exhibits a PCE of 21.35 % (6.5×7 cm) with a Voc of 8.761 V and FF of 79.1 %. The unencapsulated PSCs exhibit superior stability to devices employing spiro-OMeTAD, retaining nearly 90 % of their initial efficiency after 1000 h operation output. This work demonstrates the high potential of molecularly engineered spirobi[acridine] derivatives as HTMs as replacements for spiro-OMeTAD.

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.

Highly Efficient and Stable Perovskite Solar Modules Based on FcPF6 Engineered Spiro-OMeTAD Hole Transporting Layer.

Li-TFSI doped spiro-OMeTAD is widely recognized as a beneficial hole transport layer (HTL) in perovskite solar cells (PSCs), contributing to high device efficiencies. However, the uncontrolled migration of lithium ions (Li+) during device operation has impeded its broad adoption in scalable and stable photovoltaic modules. Herein, an additive strategy is proposed by employing ferrocenium hexafluorophosphate (FcPF6) as a relay medium to enhance the hole extraction capability of the spiro-OMeTAD via the instant oxidation function. Besides, the novel Fc-Li interaction effectively restricts the movement of Li+. Simultaneously, the dissociative hexafluorophosphate group is cleverly exploited to regulate the unstable iodide species on the perovskite surface, further inhibiting the formation of migration channels and stabilizing the interfaces. This modification leads to power conversion efficiencies (PCEs) reaching 22.13% and 20.27% in 36 cm2 (active area of 18 cm2) and 100 cm2 (active area of 56 cm2) perovskite solar modules (PSMs), respectively, with exceptional operational stability obtained for over 1000 h under the ISOS-L-1 procedure. The novel FcPF6-based engineering approach is pivotal for advancing the industrialization of PSCs, particularly those relying on high-performance spiro-OMeTAD- based HTLs.

Nucleation Regulation and Mesoscopic Dielectric Screening in α-FAPbI3.

While significant advancements in power conversion efficiencies (PCEs) of α-FAPbI3perovskite solar cells (PSCs) have been made, attaining controllable perovskite crystallization is still a considerable hurdle. This challenge stems from the initial formation of δ-FAPbI3, a more energetically stable phase than the desired black α-phase, during film deposition. This disrupts the heterogeneous nucleation of α-FAPbI3, causing the formation of mixed phases and defects. To this end, polarity engineering using molecular additives, specifically ((methyl-sulfonyl)phenyl)ethylamines (MSPEs) are introduced. The findings reveal that the interaction of PbI2-MSPEs-FAI intermediates is enhanced with the increased polarity of MSPEs, which in turn expedites the nucleation of α-FAPbI3. This leads to the development of high-quality α-FAPbI3 films, characterized by vertical crystal orientation and reduced residual stresses. Additionally, the increased dipole moment of MSPE at perovskite grain boundaries attenuates Coulomb attractions among charged defects and screens carrier capture process, thereby diminishing non-radiative recombination. Utilizing these mechanisms, PSCs treated with highly polar 2-(4-MSPE) achieve an impressive PCE of 25.2% in small-area devices and 20.5% in large-area perovskite solar modules (PSMs) with an active area of 70 cm2. These results demonstrate the effectiveness of this strategy in achieving controllable crystallization of α-FAPbI3, paving the way for scalable-production of high-efficiency PSMs.

Equally Efficient Perovskite Solar Cells and Modules Fabricated via N-Ethyl-2-Pyrrolidone Optimized Vacuum-Flash.

Efficiency reduction in perovskite solar cells (PSCs) during the magnification procedure significantly hampers commercialization. Vacuum-flash (VF) has emerged as a promising method to fabricate PSCs with consistent efficiency across scales. However, the slower solvent removal rate of VF compared to the anti-solvent method leads to perovskite films with buried defects. Thus, this work employs low-toxic Lewis base ligand solvent N-ethyl-2-pyrrolidone (NEP) to improve the nucleation process of perovskite films. NEP, with a mechanism similar to that of N-methyl-2-pyrrolidone in FA-based perovskite formation, enhances the solvent removal speed owing to its lower coordination ability. Based on this strategy, p-i-n PSCs with an optimized interface attain a power conversion efficiency (PCE) of 24.19% on an area of 0.08 cm2. The same nucleation process enables perovskite solar modules (PSMs) to achieve a certified PCE of 23.28% on an aperture area of 22.96 cm2, with a high geometric fill factor of 97%, ensuring nearly identical active area PCE (24%) in PSMs as in PSCs. This strategy highlights the potential of NEP as a ligand solvent choice for the commercialization of PSCs.

Synergistic Redox Modulation for High-Performance Nickel Oxide-Based Inverted Perovskite Solar Modules.

Nickel oxide (NiOx)-based inverted perovskite solar cells stand as promising candidates for advancing perovskite photovoltaics towards commercialization, leveraging their remarkable stability, scalability, and cost-effectiveness. However, the interfacial redox reaction between high-valence Ni4+ and perovskite, alongside the facile conversion of iodide in perovskite into I2, significantly deteriorates the performance and reproducibility of NiOx-based perovskite photovoltaics. Here, potassium borohydride (KBH4) is introduced as a dual-action reductant, which effectively avoids the Ni4+/perovskite interface reaction and mitigates the iodide-to-I2 oxidation within perovskite film. This synergistic redox modulation significantly suppresses nonradiative recombination and increases the carrier lifetime. As a result, an impressive power conversion efficiency of 24.17% for NiOx-based perovskite solar cells is achieved, and a record efficiency of 20.2% for NiOx-based perovskite solar modules fabricated under ambient conditions. Notably, when evaluated using the ISOS-L-2 standard protocol, the module retains 94% of its initial efficiency after 2000 h of continuous illumination under maximum power point at 65 °C in ambient air.

Efficient and Stable Perovskite Solar Modules Enabled by Inhibited Escape of Volatile Species.

The intrinsically weak bonding structure in halide perovskite materials makes components in the thin films volatile, leading to the decomposition of halide perovskite materials. The reactions within the perovskite film are reversible provided that components do not escape the thin films. Here, a holistic approach is reported to improve the efficiency and stability of PSMs by preventing the effusion of volatile components. Specifically, a method for in situ generation of channel barrier layers for perovskite photovoltaic modules is developed. The resulting PSMs attain a certified aperture PCE of 21.37%, and possess remarkable continuous operation stability for maximum power point tracking (MPPT) of T90 > 1100 h in ambient air, and damp heat (DH) tracking of T93 > 1400 h.

An Equalized Flow Velocity Strategy for Perovskite Colloidal Particles in Flexible Perovskite Solar Cells.

The non-uniform distribution of colloidal particles in perovskite precursor results in an imbalanced response to the shear force during flexible printing process. Herein, it is observed that the continuous disordered migration occurring in perovskite inks significantly contributes to the enlargement of colloidal particles size and diminishes the crystallization activity of the inks. Therefore, a molecular encapsulation architecture by glycerol monostearate to mitigate colloidal particles collisions in the precursor ink, while simultaneously homogenizing the size distribution of perovskite colloids to minimize their diffusion disparities, is devised. The utilization of colloidal particles with a molecular encapsulation structure enables the achievement of uniform deposition during the printing process, thereby effectively balancing the crystallization rate and phase transition in the film and facilitating homogeneous crystallization of perovskite films. The large-area flexible perovskite device (1.01 cm2 and 100 cm2) fabricated through printing processes, achieves an efficiency of 24.45% and 15.87%, respectively, and manifests superior environmental stability, maintaining an initial efficiency of 91% after being stored in atmospheric ambiences for 150 days (unencapsulated). This work demonstrates that the dynamic evolution process of colloidal particles in both the precursor ink and printing process represents a crucial stride toward achieving uniform crystallization of perovskite films.

Efficient and Stable Inverted Perovskite Solar Modules Enabled by Solid-Liquid Two-Step Film Formation.

A considerable efficiency gap exists between large-area perovskite solar modules and small-area perovskite solar cells. The control of forming uniform and large-area film and perovskite crystallization is still the main obstacle restricting the efficiency of PSMs. In this work, we adopted a solid-liquid two-step film formation technique, which involved the evaporation of a lead iodide film and blade coating of an organic ammonium halide solution to prepare perovskite films. This method possesses the advantages of integrating vapor deposition and solution methods, which could apply to substrates with different roughness and avoid using toxic solvents to achieve a more uniform, large-area perovskite film. Furthermore, modification of the NiOx/perovskite buried interface and introduction of Urea additives were utilized to reduce interface recombination and regulate perovskite crystallization. As a result, a large-area perovskite film possessing larger grains, fewer pinholes, and reduced defects could be achieved. The inverted PSM with an active area of 61.56 cm2 (10 × 10 cm2 substrate) achieved a champion power conversion efficiency of 20.56% and significantly improved stability. This method suggests an innovative approach to resolving the uniformity issue associated with large-area film fabrication.

Large Orientation Angle Buried Substrate Enables Efficient Flexible Perovskite Solar Cells and Modules.

Flexible perovskite solar cells (f-PSCs) have emerged as potential candidates for specific mechanical applications owing to their high foldability, efficiency, and portability. However, the power conversion efficiency (PCE) of f-PSC remains limited by the inferior contact between perovskite and flexible buried substrate. Here, an asymmetric π-extended self-assembled monolayer (SAM) (4-(9H-dibenzo[a,c]carbazol-9-yl)butyl)phosphonic acid (A-4PADCB) is reported as a buried substrate for efficient inverted f-PSCs. Employing this design strategy, A-4PADCB exhibits a significant orientation angle away from the surface normal, homogenizing the distribution of contact potentials. This enhancement improves the SAM/perovskite interface quality, controlling the growth of favorable perovskite films with low defect density and slight tensile stress. Integration of A-4PADCB into small-area f-PSCs and large-area flexible perovskite solar modules with an aperture area of 20.84 cm2 achieves impressive PCEs of up to 25.05% and 20.64% (certified 19.51%), respectively. Moreover, these optimized A-4PADCB-based f-PSCs possess enhanced light, thermal, and mechanical stability. This research paves a promising avenue toward the design of SAM-buried substrates with a large orientation angle, regulating perovskite growth, and promoting the commercialization of large-area flexible perovskite photovoltaics.

Over 19% Efficiency Perovskite Solar Modules by Simultaneously Suppressing Cation Deprotonation and Iodide Oxidation.

Perovskite solar cells (PSCs) based on sputtered nickel oxide (NiOx) hole transport layer have emerged as promising configuration due to their good stability, cost-effectiveness, and scalability. However, the adverse chemical redox reaction at the NiOx/perovskite interface remains an ever-present problem that has not yet been well solved. To address this issue before, the problems that cation deprotonation and iodide oxidation that occurred in precursor solution easily result in the interfacial chemical reaction should be prevented. Hence, we report an efficient strategy to simultaneously suppress the interfacial reaction and stabilize the precursor solution by incorporating a reducing and weakly acidic stabilizer, l-ascorbic acid (l-AA). l-AA can reduce I2 generated in the precursor solution and during the interfacial reaction to I-. Furthermore, the protons ionized by adjacent enol hydroxyl groups in l-AA effectively impede the deprotonation of organic cations in the precursor solution as well as at the NiOx/perovskite interface resulting from the chemical reaction. Attributing to the improved crystallization of the perovskite film and the suppression of the interfacial reaction by l-AA, the inverted PSC based on such good light absorber achieves an impressive power conversion efficiency (PCE) of 22.72% along with a high open-circuit voltage of 1.19 V. Notably, further introducing l-AA into the large-area solar modules by the slot-die coating method in air enables a remarkable PCE of 19.17%, which reaches one of the highest PCEs reported for inverted perovskite solar modules (PSMs) (active area >50 cm2) to date. l-AA located at the buried interface also forms a barrier layer that can prevent undesirable chemical reactions at the NiOx/perovskite interface, significantly enhancing the device stability of solar cells and PSMs. These findings in our work provide important guidance for improving the NiOx/perovskite interface and the fabrication of highly efficient, low-cost, and large-area PSMs.

LiTFSI-Free Hole Transport Materials for Robust Perovskite Solar Cells and Modules with High Efficiencies.

Lithium bis(trifluoromethane) sulfonamide (LiTFSI) and oxygen-doped organic semiconductors have been frequently used to achieve record power conversion efficiencies of perovskite solar cells (PSCs). However, this conventional doping process is time-consuming and leads to poor device stability due to the incorporation of Li ions. Herein, aiming to accelerate the doping process and remove the Li ions, we report an alternative p-doping process by mixing a new small-molecule organic semiconductor, N2,N2,N7,N7-tetrakis (4-methoxyphenyl)-9-(4-(octyloxy) phenyl)-9H carbazole-2,7-diamine (labeled OH44) and its preoxidized form OH44+(TFSI-). With this method, a champion efficiency of 21.8% has been achieved for small-area PSCs, which is superior to the state-of-the-art EH44 and comparable with LiTFSI and oxygen-doped spiro-OMeTAD. Moreover, the stability of OH44-based PSCs is improved compared with those of EH44, maintaining more than 85% of its initial efficiency after aging in an ambient condition without encapsulation for 1000 h. In addition, we achieved efficiencies of 14.7 and 12.6% for the solar modules measured with a metal mask of 12.0 and 48.0 cm2, respectively, which demonstrated the scalability of this method.

Rationally Designed Eco-Friendly Solvent System for High-Performance, Large-Area Perovskite Solar Cells and Modules.

The important but remained issue to be addressed to achieve the mass production of perovskite solar modules include a large-area fabrication of high-quality perovskite film with eco-friendly, viable production methods. Although several efforts are made to achieve large-area fabrication of perovskite, the development of eco-friendly solvent system, which is precisely designed to be fit to scale-up methods are still challenging. Herein, this work develops the eco-friendly solvent/co-solvent system to produce a high-quality perovskite layer with a bathing in eco-friendly antisolvent. The new co-solvent/additive, methylsulfonylmethane (MSM), efficiently improves the overall solubility and has a suitable binding strength to the perovskite precursor, resulting in a high-quality perovskite film with antisolvent bathing method in large area. The resultant perovskite solar cells showed high power conversion efficiency of over 24% (in reverse scan), with a good long-term stability under continuous light illumination or damp-heat condition. MSM is also beneficial to produce a perovskite layer at low-temperature or high-humidity. MSM-based solvent system is finally applied to large-area, resulting in highly efficiency perovskite solar modules with PCE of 19.9% (by aperture) or 21.2% (by active area) in reverse scan. These findings contribute to step forward to a mass production of perovskite solar modules with eco-friendly way.

Molecular Locking with All-Organic Surface Modifiers Enables Stable and Efficient Slot-Die-Coated Methyl-Ammonium-Free Perovskite Solar Modules.

The power conversion efficiency (PCE) of the state-of-the-art large-area slot-die-coated perovskite solar cells (PSCs) is now over 19%, but issues with their stability persist owing to significant intrinsic point defects and a mass of surface imperfections introduced during the fabrication process. Herein, the utilization of a hydrophobic all-organic salt is reported to modify the top surface of large-area slot-die-coated methylammonium (MA)-free halide perovskite layers. Bearing two molecules, each of which is endowed with anchoring groups capable of exhibiting secondary interactions with the perovskite surfaces, the organic salt acts as a molecular lock by effectively binding to both anion and cation vacancies, substantially enhancing the materials' intrinsic stability against different stimuli. It not only reduces the ingression of external species such as oxygen and moisture, but also suppresses the egress of volatile organic components during the thermal stability testing. The treated PSCs demonstrate efficiency of 19.28% (active area of 58.5 cm2 ) and 17.62% (aperture area of 64 cm2 ) for the corresponding mini-module. More importantly, unencapsulated slot-die-coated mini-modules incorporating the all-organic surface modifier show ≈80% efficiency retention after 7500 h (313 days) of storage under 30% relative humidity (RH). They also remarkably retain more than 90% of the initial efficiency for over 850 h while being measured continuously.

Recent Strategies for High-Performing Indoor Perovskite Photovoltaics.

The development of digital technology has made our lives more advanced as a society familiar with the Internet of Things (IoT). Solar cells are among the most promising candidates for power supply in IoT sensors. Perovskite photovoltaics (PPVs), which have already attained 25% and 40% power conversion efficiencies for outdoor and indoor light, respectively, are the best candidates for self-powered IoT system integration. In this review, we discuss recent research progress on PPVs under indoor light conditions, with a focus on device engineering to achieve high-performance indoor PPVs (Id-PPVs), including bandgap optimization and defect management. Finally, we discuss the challenges of Id-PPVs development and its interpretation as a potential research direction in the field.

Pressure-Assisted Space-Confinement Strategy to Eliminate PbI2 in Perovskite Layers toward Improved Operational Stability.

The existence of the PbI2 phase in the perovskite film is normally inevitable because of the easy sublimation of the organic component during the crystallization process under a relatively high annealing temperature. However, excess PbI2 will cause significant degradation on open current voltage (VOC) and fill factor (FF) under continuous illumination. Here, we developed a pressure-assisted space-confinement (PASC) method to enhance the phase purity of the perovskite film fabricated by the two-step spin-coating method. It was found that high pressure is more conductive to lower the sublimation rate of the organic units, and the space confinement is more favorable for the Ostwald ripening. The combination of them can easily fabricate high-quality perovskite films with large crystal grains and eliminated PbI2 remnants. As expected, the efficiency of the solar cell was improved from 20.38 to 22.26%; more importantly, the operational stability of the corresponding device had a pronounced improvement, which remains over 85% of its initial efficiency after 500 h maximum power point tracking measurement. Based on this PASC method, a prototype PSC module (PSM) with an active area of 14 cm2 was also fabricated reaching an efficiency over 17%.

Holistic Approach toward a Damage-Less Sputtered Indium Tin Oxide Barrier Layer for High-Stability Inverted Perovskite Solar Cells and Modules.

The commercialization of perovskite solar cells (PSCs) requires the development of long-term, highly operational-stable devices. An efficient barrier layer plays a key role in improving the device stability of planar PSCs. Here, we focus on the use of sputtered indium tin oxide (ITO) as a barrier layer to stop major degradations. To mitigate efficiency losses of cells with the ITO barrier, we optimized various sputtering process parameters such as ITO layer thickness, target power density, and working pressure. The fabricated planar inverted PSCs based on the novel ITO barrier optimization demonstrate a power conversion efficiency (PCE) of 19.05% on a cell area of 0.09 cm2. The encapsulated cells retained >80% of their initial efficiency after 1400 h of continuous illumination at 55 °C and 94.5% of their initial PCE after 1500 h stored in air. Employing such a holistic stabilization approach, the PSC minimodules without encapsulation achieved an efficiency of 16.4% with a designated area of 2.28 cm2 and retained approximately 80% of the initial performance after thermal stress at 85 °C for 350 h under ambient conditions.

Area-Scalable Zn2SnO4 Electron Transport Layer for Highly Efficient and Stable Perovskite Solar Modules.

The development of a scalable chemical bath deposition (CBD) process facilitates the realization of electron-transporting layers (ETLs) for large-area perovskite solar modules (PSMs). Herein, a method to prepare a uniform and scalable thick Zn2SnO4 ETL by CBD, which yielded high-performance PSMs, is reported. This Zn2SnO4 ETL exhibits excellent electrical properties and enhanced optical transmittance in the visible region. Moreover, the Zn2SnO4 ETL influences the perovskite layer formation, yielding enhanced crystallinity, increased grain size, and a smoother surface, thus facilitating electron extraction and collection from the perovskite to the ETL. Zn2SnO4 thereby yields PSMs with a remarkable photovoltaic performance, low hysteresis index, and high device reproducibility. The champion PSM exhibited a power conversion efficiency (PCE) of 22.59%, being among the highest values published so far. In addition, the CBD Zn2SnO4-based PSMs exhibit high stability, retaining more than 88% of initial efficiency over 1000 h under continuous illumination. This demonstrates that CBD Zn2SnO4 is an appropriate ETL for high-efficiency PSMs and a viable new process for their industrialization.

Natural Amino Acid Enables Scalable Fabrication of High-Performance Flexible Perovskite Solar Cells and Modules with Areas over 300 cm2.

Upscaling large-area formamidinium (FA)-based perovskite solar cells (PSCs) has been considered as one of the most promising routes for the commercial applications of this rising photovoltaics technology. Here, a natural amino acid, phenylalanine (Phe), is introduced to regulate the nucleation and crystal growth process of the large-scale coating of FA-based perovskite films. Better film coverage and larger grain sizes are observed after adding Phe. Moreover, it is found that Phe can effectively passivate defects within perovskite films and suppress the nonradiative recombination due to the strong interaction with under-coordinated Pb2+ ions in the perovskite films. Rigid PSCs based on the blade-coated perovskite films containing Phe obtain a champion efficiency of 21.95%. The corresponding unencapsulated devices also exhibit excellent ambient stability, retaining 95% of their initial efficiencies after storage in the glovebox at 20 °C for 1000 h. Further, the strategy is applied to fabricate flexible PSCs and modules on polyethylene terephthalate/indium doped tin oxide substrates via slot-die coating. Phe modified flexible devices achieve outstanding efficiencies of 20.21%, 12.1%, and 11.2% with aperture areas of 0.10, 185, and 333 cm2 , respectively. The strategy here has paved a promising way for the large-scale production of flexible PSCs.

Light-Stable Methylammonium-Free Inverted Flexible Perovskite Solar Modules on PET Exceeding 10.5% on a 15.7 cm2 Active Area.

Perovskite solar modules (PSMs) have been attracting the photovoltaic market, owing to low manufacturing costs and process versatility. The employment of flexible substrates gives the chance to explore new applications and further increase the fabrication throughput. However, the present state-of-the-art of flexible perovskite solar modules (FPSMs) does not show any data on light-soaking stability, revealing that the scientific community is still far from the potential marketing of the product. During this work, we demonstrate, for the first time, an outstanding light stability of FPSMs over 1000 h considering the recovering time (T80 = 730 h), exhibiting a power conversion efficiency (PCE) of 10.51% over a 15.7 cm2 active area obtained with scalable processes by exploiting blade deposition of a transporting layer and a stable double-cation perovskite (cesium and formamidinium, CsFA) absorber.