Perovskite Photovoltaic Technology Research Articles

Polydentate Ligand Reinforced Chelating to Stabilize Buried Interface toward High-Performance Perovskite Solar Cells.

The instability of the buried interface poses a serious challenge for commercializing perovskite photovoltaic technology. Herein, we report a polydentate ligand reinforced chelating strategy to strengthen the stability of buried interface by managing interfacial defects and stress. The bis(2,2,2-trifluoroethyl) (methoxycarbonylmethyl)phosphonate (BTP) is employed to manipulate the buried interface. The C=O, P=O and two -CF3 functional groups in BTP synergistically passivate the defects from the surface of SnO2 and the bottom surface of the perovskite layer. Moreover, The BTP modification contributes to mitigated interfacial residual tensile stress, promoted perovskite crystallization, and reduced interfacial energy barrier. The multidentate ligand modulation strategy is appropriate for different perovskite compositions. Due to much reduced nonradiative recombination and heightened interface contact, the device with BTP yields a promising power conversion efficiency (PCE) of 24.63 %, which is one of the highest efficiencies ever reported for devices fabricated in the air environment. The unencapsulated BTP-modified devices degrade to 98.6 % and 84.2 % of their initial PCE values after over 3000 h of aging in the ambient environment and after 1728 h of thermal stress, respectively. This work provides insights into strengthening the stability of the buried interface by engineering multidentate chelating ligand molecules.

Polydentate Ligand Reinforced Chelating to Stabilize Buried Interface toward High‐Performance Perovskite Solar Cells

AbstractThe instability of the buried interface poses a serious challenge for commercializing perovskite photovoltaic technology. Herein, we report a polydentate ligand reinforced chelating strategy to strengthen the stability of buried interface by managing interfacial defects and stress. The bis(2,2,2‐trifluoroethyl) (methoxycarbonylmethyl)phosphonate (BTP) is employed to manipulate the buried interface. The C=O, P=O and two −CF3 functional groups in BTP synergistically passivate the defects from the surface of SnO2 and the bottom surface of the perovskite layer. Moreover, The BTP modification contributes to mitigated interfacial residual tensile stress, promoted perovskite crystallization, and reduced interfacial energy barrier. The multidentate ligand modulation strategy is appropriate for different perovskite compositions. Due to much reduced nonradiative recombination and heightened interface contact, the device with BTP yields a promising power conversion efficiency (PCE) of 24.63 %, which is one of the highest efficiencies ever reported for devices fabricated in the air environment. The unencapsulated BTP‐modified devices degrade to 98.6 % and 84.2 % of their initial PCE values after over 3000 h of aging in the ambient environment and after 1728 h of thermal stress, respectively. This work provides insights into strengthening the stability of the buried interface by engineering multidentate chelating ligand molecules.

Preparation of high-performance large-area perovskite solar cells by atomic layer deposition of metal oxide buffer layer

Perovskite solar cells have been widely recognized as the most promising new-type photovoltaic device due to its power conversion efficiency rapidly increasing from 3.8% to over 26% in merely fifteen years. However, the high performances are achieved mainly on small area cells with an active area lower than 0.1 cm<sup>2</sup>. When enlarging the active area of perovskite solar cells, the efficiency falls dramatically. So, how to reduce the gap between performances of small area cells and large area cells gradually becomes a critical point in the path towards the commercialization of perovskite photovoltaic technology. Herein, a strategy of pre-growing thin layer of TiO<sub>2</sub> on a rough FTO substrate by atomic layer deposition method before spin-coating SnO<sub>2</sub> nanoparticles is proposed. Due to the inherent conformal film growth mode of atomic layer deposition, the FTO substrate can be completely covered by TiO<sub>2</sub>, thus preventing the direct contact between local protrusions of FTO and perovskite layer and impeding the current leakage phenomenon, which can be verified by the measurements from X-ray photoelectron spectroscopy, scanning electron microscopy, and atomic force microscopy, and further proved by the dark current measurement. By using this method, the repeatability and consistency of the small area cell fabrication technology on the same substrate are improved obviously. The improved electron transport process revealed by photoluminescence results and incident light management process revealed by external quantum efficiency results also brings about better solar cell performances. More importantly, highly efficient 0.5 cm<sup>2</sup> large area perovskite solar cells are fabricated through optimization of TiO<sub>2</sub> thickness. When growing 200 cycles TiO<sub>2</sub> (~9 nm in thickness) by using atomic layer deposition technology, the champion large area perovskite solar cell possesses a power conversion efficiency as high as 24.8% (certified 24.65%). The device performances also show excellent repeatability between different fabrication batches. The perovskite solar cell with TiO<sub>2</sub> buffer layer grown by the atomic layer deposition method can still retain over 95% of its initial efficiency after having been stored in a nitrogen atmosphere for 1500 h. The technique proposed in this paper can be helpful in manufacturing perovskite solar cell modules in the realistic photovoltaic market and can be extended to the large area fabrication of other perovskite optoelectronic devices such as light emitting diode, laser and detector.

In Situ Self-Elimination of Defects via Controlled Perovskite Crystallization Dynamics for High-Performance Solar Cells.

Understanding and controlling crystallization is crucial for high-quality perovskite films and efficient solar cells. Herein, theissue of defects in formamidinium lead iodide (FAPbI3 ) formation is addressed, focusing on the role of intermediates. A comprehensive picture of structural and carrier evolution during crystallization is demonstrated using in situ grazing-incidence wide-angle X-ray scattering, ultraviolet-visible spectroscopy and photoluminescence spectroscopy. Three crystallization stages are identified: precursors to the δ-FAPbI3 intermediate, then to α-FAPbI3 , where defects spontaneously emerge. A hydrogen-sulfate-based ionic liquid additive is found to enable the phase-conversion pathway of precursors → solvated intermediates → α-FAPbI3 , during which the spontaneous generation of δ-FAPbI3 can be effectively circumvented. This additive extends the initial growth kinetics and facilitates solvent-FA+ ion exchange, which results in the self-elimination of defects during crystallization. Therefore, the improved crystallization dynamics lead to larger grain sizes and fewer defects within thin films. Ultimately, the improved perovskite crystallization dynamics enablehigh-performance solar cells,achieving impressive efficiencies of 25.14%at 300K and 26.12% at 240K. This breakthrough might open up a new era of application for the emerging perovskite photovoltaic technology to low-temperature environments such as near-space and polar regions.

Extrinsic Interstitial Ionsin Metal HalidePerovskites: A Review.

Perovskite solar cells have rapidly developed as a promising technology for the next generation of low-cost photovoltaics, receiving enormous attention from researchers and industries. Compared to traditional semiconducting materials, metal halide perovskite exhibits outstanding tolerance to extrinsic ions. At a certain range of doping concentration, the interstitial occupancy of extrinsic ions provides appealing benefits to the perovskite films, contributing to higher performance and stability of the devices. This review summarizes the research progress of interstitial ions for metal halide perovskite, providing insights into the mechanism and identification of interstitial doping of extrinsic ions, covering the benefits of interstitial ions in regulating crystal growth, inhibiting ion migration, and reducing defect density. Finally, based on the latest progress and findings, further topics and directions of research on interstitial ions in metal halide perovskite are proposed to advance the understanding of interstitial ions in perovskite and promote the development of perovskite photovoltaic technology.

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.

Dendrimer Modification Strategy Based on the Understanding of the Photovoltaic Mechanism of a Perovskite Device under Full Sun and Indoor Light

The wide-band-gap inorganic CsPbI2Br perovskite material provides a highly matched absorption range with the indoor light spectrum and is expected to be used in the fabrication of highly efficient indoor photovoltaic cells (IPVs) and self-powered low-power Internet of Things (IoT) sensors. However, the defects that cause nonradiative recombination and ion migration are assumed to form leakage loss channels, resulting in a severe impact on the open-circuit voltage (VOC) and the fill factor (FF) of IPVs. Herein, we introduce poly(amidoamine) (PAMAM) dendrimers with multiple passivation sites to fully repair the leakage channels in the devices, taking into account the characteristics of IPVs that are extremely sensitive to nonradiative recombination and shunt resistance. The as-optimized IPVs demonstrate a promising PCE of 35.71% under a fluorescent light source (1000 lux), with VOC increased from 0.99 to 1.06 V and FF improved from 75.21 to 84.39%. The present work provides insight into the photovoltaic mechanism of perovskites under full sun and indoor light, which provides guidance for perovskite photovoltaic technology with industrialization prospects.

Reaching Highly Uniform Perovskite Ink Flow from a Slot‐Die Head Toward Printed Solar Cells

Large‐scale manufacturing of perovskite solar cells (PSCs) requires the deposition of homogeneous and defect‐free perovskite films on large‐area substrates. Up to now, the knowledge developed for industrial slot‐die processing has not been fully transferred to the perovskite photovoltaic community. Here, the deposition of uniform perovskite layers by slot‐die coating (SDC). Computer fluid dynamics (CFD) simulations, experimental validation, and calculation of industrial uniformity parameters are demonstrated, which enabled to establish processing conditions for SDC of perovskite ink. This approach allowed for obtaining stable cross‐web flow in the slot‐die head resulting in the formation of a stable coating bead yielding uniform perovskite films. The best processing parameters are used for the fabrication of slot‐die‐coated PSCs, which showed a more homogeneous spatial distribution of photovoltaic parameters compared to their spin‐coated counterparts. Better reproducibility observed in device performance is a step forward toward the commercialization of perovskite photovoltaic technology. For the first time, the industrial approach used for the optimization of slot‐die coating is applied for the processing of perovskite inks that have special conditions such as low viscosity and in situ crystallization on the substrate.

Hole-Transporting Self-Assembled Monolayer Enables Efficient Single-Crystal Perovskite Solar Cells with Enhanced Stability

The difficulty of growing perovskite single crystals in configurations suitable for efficient photovoltaic devices has hampered their exploration as solar cell materials, despite their potential to advance perovskite photovoltaic technology beyond polycrystalline films through markedly lower defect densities and desirable optoelectronic properties. While polycrystalline film absorbers can be deposited on myriad substrates, perovskite single crystals fit for high-efficiency devices have only been demonstrated on hydrophobic hole-transport layers [HTLs, e.g., poly(triaryl amine) (PTAA)], which has severely restricted the avenues for enhancing device efficiency and stability. Herein, we report the growth of mixed-cation FA0.6MA0.4PbI3 perovskite single crystals on a hydrophilic self-assembled monolayer {SAM, [2-(3,6-dimethoxy-9H-carbazol-9-yl)ethyl]phosphonic acid), (MeO-2PACz)} HTL surface. Compared with PTAA, the MeO-2PACz SAM promotes the mechanical adhesion of the perovskite on the substrate, enabling the fabrication of inverted solar cells with substantially enhanced operational stability and power conversion efficiencies of up to 23.1%, setting a new benchmark for single-crystal perovskite solar cells.

Opportunities and Challenges for Perovskite Solar Cells Based on Vacuum Thermal Evaporation

AbstractDeveloping an effective scalable fabrication process for perovskite solar cells is urgent to getting perovskite photovoltaic technology market‐ready. Perhaps due to the relatively cost‐effective setup and tunable fabrication processes, the vast majority of research efforts have been dedicated to the development of solution‐based scalable processes. Comparatively, the vacuum thermal evaporation processes have not been studied in‐depth, regardless of their advantages in reproducibility, scalability, extendable applications, safety, and toxicity. Here possible opportunities and challenges are discussed in utilizing the vacuum thermal evaporation technique for mass production of large‐area perovskite solar modules. While this process has technical and economical potential, more research should be warranted.

Can Nanosecond Laser Achieve High‐Performance Perovskite Solar Modules with Aperture Area Efficiency Over 21%?

AbstractOvercoming cell‐to‐module (CTM) efficiency losses is indispensable to realize large‐area high‐efficiency perovskite photovoltaic devices for commercialization. Laser scribing technology is used to fabricate perovskite modules, but it does not seem to solve the problem of high‐quality interconnection and high geometric filling factor (GFF), which are the prerequisites for overcoming CTM losses. In reality, what kind of laser technology is needed to fabricate high‐efficiency perovskite solar modules is still an open question. Herein, this work demonstrates that a nanosecond pulse laser is able to deliver a reduced heat‐affected zone due to the small thermal diffusion coefficient (Dt) of perovskite material, contributing to the accomplishment of a high GFF of up to 95.5%. In addition, the monolithic interconnection quality is improved by finely lifting off the capping layers on indium tin oxide and identifying the residue within the scribed area. As a result, a certified aperture area efficiency of 21.07% under standard 100 mW cm−2 AM1.5G illumination is achieved with a high photovoltaic fill factor exceeding 80%. The present study provides guidance in overcoming key CTM efficiency losses in perovskite photovoltaic technology.

PERFORMANCE SIMULATION OF ECO-FRIENDLY SOLAR CELLS BASED ONCH3NH3SnI3

Large-scale deployment of the perovskite photovoltaic technology using such high-performance materials as СH3NH3PbI3may face serious environmental issuesin the future. Implementation of perovskite solar cellbased on Sncouldbe an alternative solution for commercialisation. This paperpresents the results of a theoretical study of a lead-free, environmentally-friendlyphotovoltaic cellusing СH3NH3SnI3as a light-absorbing layer. The characteristics of a photovoltaic cell based on perovskite were modelled using the SCAPS-1D program. Various thicknesses of the absorbing layer were analysed,and an optimised device structure is proposed,demonstratinga high power conversionefficiencyof up to 28% at ambient temperature. The analysis of the thicknesses of the СH3NH3SnI3absorbing layer revealedthat at a thickness of 500 nm, performance is demonstrated with an efficiencyof 27.41 %, a fill factor of 85.92 %, a short circuit current density of 32.60 mA/cm2and an open-circuit voltage of 0.98 V. The obtained numerical results indicate that the СH3NH3SnI3absorbing layer may be a viable replacement forthe standard materials and may form the basis of a highly efficient technology of the environmentally-friendlyperovskite solar cells.

Hysteresis‐Free Planar Perovskite Solar Module with 19.1% Efficiency by Interfacial Defects Passivation

In few years, perovskite solar devices have reached high efficiency on lab scale cells. Upscaling to module size, effective perovskite recipe and posttreatment are of paramount importance to the breakthrough of the technology. Herein this work, the development of a low‐temperature planar n–i–p perovskite module (11 cm2 aperture area, 91% geometrical fill factor) is reported on, exploiting the defect passivation strategy to achieve an efficiency of 19.1% (2% losses stabilized) with near‐zero hysteresis, that is the most unsolved issue in the perovskite photovoltaic technology. The I/Br (iodine/bromide) halide ion ratio of the triple‐cation perovskite formulation and deposition procedure are optimized to move from small area to module device and to avoid the detrimental effect of dimethyl sulfoxide (DMSO) solvent. The organic halide salt phenethylammonium iodide (PEAI) is adopted as surface passivation material on module size to suppress perovskite defects. Finally, homogeneous and defect‐free layers from cell to module with only 8% relative efficiency losses, high reproducibility, and optimized interconnections are scaled by laser ablation methods. The homogeneity of the perovskite layers and of the full stack was assessed by optical, morphological, and light beam–induced current (LBIC) mapping characterizations.

Industrially Compatible Fabrication Process of Perovskite-Based Mini-Modules Coupling Sequential Slot-Die Coating and Chemical Bath Deposition.

To upscale the emerging perovskite photovoltaic technology to larger-size modules, industrially relevant deposition techniques need to be developed. In this work, the deposition of tin oxide used as an electron extraction layer is established using chemical bath deposition (CBD), a low-cost and solution-based fabrication process. Applying this simple low-temperature deposition method, highly homogeneous SnO2 films are obtained in a reproducible manner. Moreover, the perovskite layer is prepared by sequentially slot-die coating on top of the n-type contact. The symbiosis of these two industrially relevant deposition techniques allows for the growth of high-quality dense perovskite layers with large grains. The uniformity of the perovskite film is further confirmed by scanning electron microscopy (SEM)/scanning transmission electron microscopy (STEM) analysis coupled with energy dispersive X-ray spectroscopy (EDX) and cathodoluminescence measurements allowing us to probe the elemental composition at the nanoscale. Perovskite solar cells fabricated from CBD SnO2 and slot-die-coated perovskite show power conversion efficiencies up to 19.2%. Furthermore, mini-modules with an aperture area of 40 cm2 demonstrate efficiencies of 17% (18.1% on active area).

Toward Commercialization of Efficient and Stable Perovskite Solar Modules

The commercialization of perovskite photovoltaic technology is dependent on the development of high‐efficiency, stable, and large‐area solar modules. Despite the rapid rise in efficiencies of laboratory‐scale perovskite solar cells (PSCs), there is still a big gap in the transition from small‐area devices to large‐area perovskite solar modules (PSMs). Herein, recent progresses on scaling‐up PSMs are reviewed: first, multifarious scalable preparation methods, solvent engineering, and corresponding morphology control strategies for large‐area homogeneous perovskite films are summarized. Various charge carrier transport materials, electrode materials, and their scaling methods for high‐efficiency and stable PSMs are then outlined and the device structure design of PSMs is discussed. Finally, the current strategies for optimizing the environmental stability of devices are highlighted, and packaging for reducing lead leakage during operation is discussed.

Laser Processing Methods for Perovskite Solar Cells and Modules

AbstractThe perovskite photovoltaic technology is now transitioning from basic research to the pre‐industrialization phase. In order to achieve reliable and high‐performance commercial perovskite solar modules, high throughput manufacturing technologies must now be adapted to the specific constraints and requirements imposed by the perovskite solar cells unique new chemistries, film deposition methodologies, and encapsulation requirements. Laser technologies will play an important role in the industrialization of these devices, both to achieve high active surface area modules and for the deposition and/or treatment of the critical layers. Industrial lasers will be essential to achieve active areas greater than 95% of the total area to retain the benefits of the very high performances reported for <1 cm2 laboratory cells. The speed of laser processing for the preparation of interconnects is unrivalled by comparison to other structuring methods. Recent reports of the use of lasers in upscaling perovskite solar cells are presented and analyzed here.

Accelerated Thermal Aging Effects on Carbon‐Based Perovskite Solar Cells: A Joint Experimental and Theoretical Analysis

In the search for stable perovskite photovoltaic technology, carbon‐based perovskite solar cells (C‐PSCs) represent a valid, stable solution for near‐future commercialization. However, a complete understanding of the operational device stability calls for assessing the device robustness under thermal stress. Herein, the device response is monitored upon a prolonged thermal cycle aging (heating the device for 1 month up to 80 °C) on state‐of‐the‐art C‐PSCs, often neglected, mimicking outdoor conditions. Device characterization is combined with in‐house‐developed advanced modeling of the current–voltage characteristics of the C‐PSCs using an iterative fitting method based on the single‐diode equation to extrapolate series (RS) and shunt (RSH) resistances. Two temperature regimes are identified: Below 50 °C C‐PSCs are stable, and switching to 80 °C a slow device degradation takes place. This is associated with a net decrease of the device RSH, whereas the RS is unaltered, pointing to interface deterioration. Indeed, structural and optical analyses, by means of X‐ray diffraction and photoluminescence studies, reveal no degradation of the perovskite bulk, providing clear evidence that perovskite/contact interfaces are the bottlenecks for thermal‐induced degradation in C‐PSCs.

Sputtered Ga-Doped SnOx Electron Transport Layer for Large-Area All-Inorganic Perovskite Solar Cells.

The scalability processing of all functional layers in perovskite solar cells (PSCs) is one of the critical challenges in the commercialization of perovskite photovoltaic technology. In response to this issue, a large-area and high-quality gallium-doped tin oxide (Ga-SnOx) thin film is deposited by direct current magnetron sputtering and applied in CsPbBr3 all-inorganic PSCs as an electron transport layer (ETL). It is found that oxygen defects of SnOx can be remarkably offset by regulating oxygen flux and acceptor-like Ga doping level, resulting in higher carrier mobility and suitable energy level alignment, which is beneficial in accelerating electron extraction and suppressing charge recombination at the perovskite/ETL interface. At the optimal O2 flux (12 sccm) and Ga doping level (5%), the device based on sputtered Ga-SnOx ETL without any interface modification shows a power conversion efficiency (PCE) of 8.13%, which is significantly higher than that of undoped SnOx prepared by sputtering or spin coating. Furthermore, a PCE of 5.98% for a device with an active area of 1 cm2 is obtained, demonstrating great potential in fabricating efficient and stable large-area PSCs.

Trapping lead in perovskite solar modules with abundant and low-cost cation-exchange resins

One major concern for the commercialization of perovskite photovoltaic technology is the toxicity of lead from the water-soluble lead halide perovskites that can contaminate the environment. Here, we report an abundant, low-cost and chemically robust cation-exchange resin (CER)-based method that can prevent lead leakage from damaged perovskite solar modules under severe weather conditions. CERs exhibit both high adsorption capacity and high adsorption rate of lead in water due to the high binding energy with lead ions in the mesoporous structure. Integrating CERs with carbon electrodes and layering them on the glass surface of modules has a negligible detrimental effect on device efficiency while reducing lead leakage from perovskite mini-modules by 62-fold to 14.3 ppb in water. The simulated lead leakage from damaged large-area perovskite solar panels treated with CERs can be further reduced to below 7.0 ppb even in the worst-case scenario that every sub-module is damaged. Lead leakage from damaged perovskite photovoltaic modules poses health and environmental risks limiting the potential use of the technology. Now Chen et al. show that the encapsulation of perovskite modules with a cation-exchange resins reduces lead leakage to 14.3 ppb in waste water.

2D metal-organic framework for stable perovskite solar cells with minimized lead leakage.

Despite the notable progress in perovskite solar cells, maintaining long-term operational stability and minimizing potentially leaked lead (Pb2+) ions are two challenges that are yet to be resolved. Here we address these issues using a thiol-functionalized 2D conjugated metal-organic framework as an electron-extraction layer at the perovskite/cathode interface. The resultant devices exhibit high power conversion efficiency (22.02%) along with a substantially improved long-term operational stability. The perovskite solar cell modified with a metal-organic framework could retain more than 90% of its initial efficiency under accelerated testing conditions, that is continuous light irradiation at maximum power point tracking for 1,000 h at 85 °C. More importantly, the functionalized metal-organic framework could capture most of the Pb2+ leaked from the degraded perovskite solar cells by forming water-insoluble solids. Therefore, this method that simultaneously tackles the operational stability and lead contamination issues in perovskite solar cells could greatly improve the feasibility of large-scale deployment of perovskite photovoltaic technology.