Processing Of Perovskite Solar Cells Research Articles

Facile eco-friendly process for upcycled sustainable perovskite solar cells

Developing a green technology to eliminate the impact of the toxic element Pb and harmful solvent is a challenge for sustainable perovskite solar cells (PSCs). Herein, we report a facile eco-friendly process for upcycled sustainable PSC by screening the polar Pb solubilizers (N,N-dimethylformamide, DMF, dimethyl sulfoxide, DMSO and butylamine, BA) coupling with multi-function potassium iodide (KI) precipitator. We find that DMF with strong Pb-dissolution capacity and weak coupled C = O − Pb adhesion exhibits superb separation and recovery of Pb from obsolete PSC devices. Subsequent closed-loop management of the DMF completely eliminates its potential harm to the ecological environment. Interestingly, the KI precipitator added to the Pb-containing DMF solution not only induces the formation of high-quality PbI2 and thus high-crystallized defect-less perovskite matrix, but also relieves the residual tensile strain stemming from lattice expansion leading to orderly lattice orientation for perovskite crystallization. As a result, the re-fabricated PSC based on recovered components (PbI2, ITO and Ag) shows a PCE of 22.78 % higher than that (20.76 %) of PSC based on fresh components, also exceeding the reported record efficiency of PSCs based on one or more recovered components. Such a stable, environment-friendly, upcycled process of retired PSCs offers a sustainable pathway for eliminating the adverse factors such as toxic Pb leakage and harmful solvent effluence, and thus boost their competitiveness in future energy market.

Encapsulating perovskite solar cells for long-term stability and prevention of lead toxicity

Lead halide perovskite solar cells (PSCs) have achieved remarkable efficiencies comparable to those of their established silicon counterparts at a very fast pace. Moreover, solution-processable facile technologies offer low-cost, low-temperature, scalable fabrication of these solar cells. Numerous studies have focused on improving the performance, stability, and processing of PSCs. However, potential lead toxicity and poor long-term stability impede their commercialization. In recent years, several studies have developed novel encapsulants for PSCs that can simultaneously improve stability and impede potential lead leakage. Although improvements have been made on both fronts, no solution to date could achieve a level of stability and leakage prevention that could result in a market breakthrough. Here, we analyze PSC encapsulation and lead leakage prevention techniques undertaken in recent years. While most of the related studies focused on improving either stability or toxicity, we note that both can be solved together with a suitable encapsulant that is impermeable to both moisture and Pb2+ ions. In addition, the lack of a unified standard stability testing protocol has led to stability testing under a variety of temperatures, humidities, and environmental conditions. Therefore, the urgency for a standard protocol for stability and lead toxicity testing cannot be overlooked.

Dual-meniscus-assisted roller-coating for scalable and patterned perovskite solar cells

Scaling up the fabrication process for perovskite solar cells has emerged as a prominent research focus in the field of perovskite photovoltaics. Current methods for preparing large-scale perovskite solar cells often struggle to meet the simultaneous requirements of continuous production, high compatibility, and low commissioning costs necessary for industrial-scale manufacturing. Here, the roller coating method is demonstrated to realize the preparation of large-scaled and uniform perovskite films with customized patterning through a facile and stable “touch-and-roll” motion. The unique fabric-based roller and “dual-meniscus” structure guarantee accurate control of ink flow and film thickness, thereby realizing the reproducible preparation on different substrates ranging from rigid glass to flexibe polymer film. The method yielded PSCs with peak efficiencies of 14.11% (0.16 cm2) and 10.61% (1 cm2). This roller coating method exhibits a promising new avenue for advancing the scale and commercial development of perovskite photovoltaics.

Decoding Polymeric Additive‐Driven Self‐Healing Processes in Perovskite Solar Cells from Chemical and Physical Bonding Perspectives

AbstractThis review addresses the self‐healing effects in perovskite solar cells (PSCs), emphasizing the significance of chemical and physical bonding as core mechanisms. Polymeric additives play a vital role in inducing self‐healing phenomena along with the intrinsic properties of perovskite materials, both of which are discussed herein. As a relatively underexplored area, the self‐healing effect induced by polymeric additives in PSCs is reviewed from a chemical perspective. The chemical bonds involved in self‐healing include isocyanate, disulfide, and carboxylic acid groups. The physical bonds related to self‐healing effects are primarily hydrogen bonding and chelation. Self‐healing in flexible perovskite devices extends their lifespan and improves their mechanical robustness against environmental and mechanical stressors. This discussion delves into the initiation methods for self‐healing, the conditions required, and the recovery‐rate profiles. This review not only catalogs various approaches to self‐healing, but also considers the fundamental limitations and potential of this phenomenon in PSCs. In addition, insights and an outlook on self‐healing in perovskite‐based optoelectronics are provided, offering guidance for future research and applications.

Low-temperature synergistic effect of MA and Cl towards high-quality α-FAPbI3 films for humid-air-processed perovskite solar cells.

Due to the hydrophilicity and black-phase instability of FA perovskites, ambient humidity is an unavoidable issue in the processing of perovskite solar cells (PSCs). MACl is among the most popular additives for improving perovskite films, but our experiments confirm that the direct addition of MACl into the precursor solution deteriorates the stability of the final α-FAPbI3 films in humid air, which is attributed to the unwanted pinholes induced by MACl volatilization. To solve this problem, a novel confined-space annealing strategy (CSA) is intentionally developed to control the amount of MACl at a low level. Through retarding the volatilization of MACl and blocking moisture ingress, dense and δ-phase-free FAPbI3 films with excellent crystallinity and stability are achieved at 100 °C under high humidity (RH: 60 ± 10%). We further compare the same amounts of MAI and FACl additives with MACl, discovering that only when MA and Cl work together can pure α-FAPbI3 films be obtained; therefore, a mechanism of MA-assisted nucleation and Cl-induced diffusion recrystallization is inferred. As a result, the PSCs employing optimal films yield a champion power conversion efficiency (PCE) of 17.27% and retain over 90% of the initial PCE after exposure to high humidity for 480 h. Our results offer deep insights into the thermodynamic and kinetic behaviors of MA and Cl in film growth and are beneficial for air-processed FA-based PSCs for commercial application.

Efficient MAPbI3-based perovskite solar cells exceeding 21% efficiency via aging treatment

Recently, the demand for large-area and high-efficiency perovskite solar cells (PSCs) has increased, and a two-step process for high-efficiency large-area PSCs is actively being studied. However, the two-step process is still less efficient than the one-step antisolvent dripping process owing to the poor interdiffusion of organic components. In this study, a perovskite layer using a hybrid deposition method in which an excess of methylammonium iodide (MAI) solution is reacted with thermally evaporated PbI2 is reported. The perovskite film quality is improved by reacting unreacted residual PbI2 with excess MAI by applying daily electrical stress and aging for 60 days in a glovebox. The best PSC exhibits a PCE of 21.1 %, the highest reported power conversion efficiency among PSCs based on the two-step hybrid deposited MAPbI3 perovskite, with a large enhanced open-circuit voltage of 1.21 V and fill factor of 80.8 %. Moreover, using the solvent pre-heat treatment method, the reaction of unreacted PbI2 with MAI is accelerated, and the aging time of PSCs is shortened from 60 to 7 days, showing a PCE value of 20.7 %. Furthermore, we present a large-area PSC with a PCE of 19.4 %, indicating that the PCE can be improved through the hybrid deposition method.

Green solvent enabled scalable processing of perovskite solar cells with high efficiency

Green solvent enabled scalable processing of perovskite solar cells with high efficiency

Preparation of High Geometric Filling Factor Perovskite Module and Feasibility Study on Electrocatalytic Hydrogen Production

In recent years, perovskite solar cells have achieved high efficiency in small areas, but the industrialization of perovskite solar cells is still hampered by the efficiency loss of cells during area scaling. Series modules are currently the most widely used and effective modular process for perovskite solar cells, a process that requires the patterning of the layer stack in individual cells. This interconnection scheme consists of three lines, P1–P3, which are ablated using a pulsed laser beam. In this work, we developed an efficient perovskite module with a high geometric fill factor (GFF) based on a two-step spin-coating method by optimizing the laser ablation step. We constructed the entire device structure by means of a picosecond green pulsed laser, meanwhile, the dead area is greatly reduced by optimizing the parameters and process, and finally achieving an ultra-high GFF of over 99%. In addition, we investigated the effect of poor P2 and P3 ablation on the perovskite solar modules and compared the performance of the module before and after ablation optimization. We finally obtained a maximum photoelectric conversion efficiency of 22.79% with an aperture area of 12.6 cm2. Concurrently, we conducted electrocatalytic hydrogen production experiments on the prepared perovskite solar modules, and the experimental results have also shown excellent performance and good prospects.

Incorporation of carbon nanotubes in hole transport materials for perovskite solar cells

ABSTRACT Many loss processes in perovskite solar cells (PSCs) take place at interfaces. One effective mitigation strategy is introducing carbon derivatives at the interface of the charge transport layers with the halide perovskite absorber and/or with the contacts. In this work, single-walled carbon nanotubes are incorporated into the hole transporting material (HTM), either as composites or as a separate layer on top of the HTM. Both organic and inorganic hole transport materials are studied to validate this approach for different types of HTMs. It is shown that the CNTs facilitate charge transport from perovskite to the back contact, regardless of the HTM used. The use of CNTs results in an increase in a significant increase in short circuit current and power conversion efficiency. This study illustrates how SWCNTs can be utilised to improve the properties of a wide range of HTMs, which will pave the way for more efficient and PSCs.

Single‐Source Vapor‐Deposition of MA1–xFAxPbI3 Perovskite Absorbers for Solar Cells

AbstractVapor deposition of halide perovskites presents high potential for scalability and industrial processing of perovskite solar cells. It prevents the use of toxic solvents, allows thickness control, and yields conformal and uniform coating over large areas. However, the distinct volatility of the perovskite organic and inorganic components currently requires the use of multiple thermal sources or two‐step deposition to achieve the perovskite phase. In this work, single‐source, single‐step MA1–xFAxPbI3 thin film deposition with tunable stoichiometry by pulsed laser deposition is demostrated. By controlling the laser ablation of a solid target containing adjustable MAI:FAI:PbI2 ratios, the room temperature formation of cubic α‐phase MA1–xFAxPbI3 thin films is demonstrated. The target‐to‐film transfer of the ablated species, including the integrity of the organic molecules and the desired MA+:FA+ ratio, is confirmed by x‐ray photoelectron spectroscopy and solid‐state NMR. Photoluminescence analysis further confirms the shift of the bandgap with varying the MA+:FA+ ratio. Finally, proof‐of‐concept n‐i‐p solar cells with 14% efficiency are demonstrated with as‐deposited non‐passivated pulsed laser deposition (PLD)‐MA1–xFAxPbI3. This study opens the path for future developments in industry‐compatible vapor‐deposition methods for perovskite solar cells.

Effect of the TiO2 electron transport layer thickness on charge transfer processes in perovskite solar cells

Dense TiO2 thin films are widely used as electron transport layers in perovskite solar cells. TiO2 is a high band gap semiconductor with n-type conductivity showing excellent compatibility with metal-halide perovskites in terms of energy alignment providing efficient charge separation and less energy loss of electrons during electron transfer. In this work, TiO2 layers were deposited from TiO2 sol-gel solution by spin-coating methods. The optimization of TiO2 ETL thickness is a necessary procedure to reduce ETL resistance and minimize charge recombination. The thickness reduction leads to a decrease in resistance, however, also enhances charge recombination due to the formation of pin-holes and cracks. We found that TiO2 thickness reduction also causes the TiO2 defects density changes. By studying luminescence spectra of TiO2 with various thicknesses we found that the thickness reduction leads to the increase in the interstitial Ti+3 defects density, while the oxygen vacancies density decreases. Ti+3 species form deep levels trapping free electrons and as result increasing TiO2 resistance. TiO2 films with thicknesses in the range of 40–120 nm were deposited and used as ETL for PSCs with ITO/TiO2/CH3NH3I3PbClx/CuPc/MoOx/Ag structure. Our study revealed two competitive charge transport processes taking place in TiO2: electron transport through the TiO2 conduction band and electron trapping by deep trap levels formed by Ti+3 species. Therefore according to the IV and IS studies, the optimal TiO2 layer thickness at which there is a balance between the competitive charge transport processes is about 60 nm for our deposition condition.

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.

Methylammonium Chloride Additive in Lead Iodide Optimizing the Crystallization Process for Efficient Perovskite Solar Cells

Perovskite solar cells (PSCs) were fabricated using a two-step spin-coating method with MACl added to the inorganic layer. The properties of the perovskite films were characterized by SEM, XRD, PL, UV-vis spectra, etc. The morphology of the PbI2 film was significantly changed, and the formation of MACl-related intermediate phase was observed at the grain boundaries. The grain size and crystallinity of the perovskite film increased, and the morphology at grain boundaries was optimized, while the composition of perovskite remained unchanged. The introduction of MACl improved the open circuit voltage (VOC) and fill factor (FF) of PSCs, and the optimal device efficiency reached 21.59%. This paper presents a new approach using additives in inorganic layers to optimize the crystallization process for efficient PSCs.

Reactive Inhibition Strategy for Triple‐cation Mixed‐halide Perovskite Ink with Prolonged Shelf‐life

AbstractSolution processing of perovskite solar cells (PSCs) is highly promising for the high‐throughput production of cost‐effective devices. Although PSCs have achieved great advances in power conversion efficiency, challenges still remain in the reproducibility of high‐quality perovskite thin film with simultaneously improved precursor solution stability. Here, a reactive inhibition strategy by introducing diethyl (hydroxymethyl) phosphonate (DHP) in perovskite precursor solution is successfully employed to improve the stability of precursor solution and the performance of corresponding device. DHP inhibits the reactivity of the iodide and formamidinium ions through multiple chemical bonds, ensuring the stability of the precursor solution. In addition, due to chelation interaction of Pb2+ with the oxygen of PO in DHP, the DHP in the perovskite film improves the film quality with desired stoichiometry by reducing the defects and the content of lead iodide. The DHP‐doped precursor solution and corresponding devices show excellent performance reproducibility and super stability under ambient conditions for more than 50 days, which illustrates the commercial feasibility for scalable fabrication.

Modeling and Balancing the Solvent Evaporation of Thermal Annealing Process for Metal Halide Perovskites and Solar Cells.

Triple-mesoscopic perovskite solar cells (PSCs) have attracted intensive attention due to the high stability, simple fabrication process, and low material cost. In this structure, the perovskite layer is hosted by a triple-mesoscopic scaffold of TiO2 /ZrO2 /carbon, and thus the crystal quality is sensitive to the thermal annealing process. Typically, the annealing process is conducted in a petri dish, for which the solvent evaporation of the perovskite precursor is slowed down, but not controllable and designable. To control the solvent evaporation, annealing chambers are first designed with different shape and vapor releasing channels. Then, physical simulations are performed by a finite element method, and it is found out that the chamber with a crowned top and releasing channels on the bottom sides can realize homogeneous distribution of the solvent vapor. To verify the simulation results, chambers are fabricated by 3D printing technique, for which the printing deviation can be as low as 100 µm. By balancing the solvent evaporation and release, the optimal solvent evaporation is achieved of the perovskite precursor in the triple-mesoscopic scaffold. This work offers a method to obtain homogeneous distribution of solvent vapor, and provides a new insight into understanding the influence of solvent evaporation during the thermal annealing process for PSCs.

Low‐Temperature‐Processed Stable Perovskite Solar Cells and Modules: A Comprehensive Review

AbstractThe impending commercialization of perovskite solar cells (PSCs) is plodding despite the booming power conversion efficiencies and high stabilities. Most high‐performance, stable PSCs are often processed partially with high‐temperature processes, increasing the cost of production and energy payback time. Low‐temperature‐processed PSCs are crucial as they cut down the expenses lowering the barriers to industrial use. In addition, low‐temperature‐processed methods have a wide range of applicability in flexible devices and for tandem applications with other photovoltaic technologies where the temperature budget is limited. Therefore, making stable PSCs under ambient conditions as well as providing low‐cost fabrication techniques is highly desirable. Here, a detailed review is presented on the development of the low‐temperature process strategies for fabricating highly stable PSCs and perovskite solar modules. The effectiveness of low‐temperature processing in various classes of materials is also discussed. First, the authors introduce some major degradation processes in PSCs. Then, the developments and evolving strategies of notable materials using low‐temperature processing routes and a correlation with stability are summarized. A few general trends which are related to stability are also discussed. Overall, this review contributes to a better understanding of the status of low‐temperature‐processed cells and modules.

DFT and TDDFT investigation of four triphenylamine/phenothiazine-based molecules as potential novel organic hole transport materials for perovskite solar cells

Hole transport materials (HTMs) based on conductive organic molecules are crucial components to prepare highly efficient perovskite solar cells (PSCs). To overcome the limitations arising from the use of the most common Spiro-OMeTAD, hindering large-scale PSCs production, alternative HTMs are highly desirable. Therefore, several fully organic molecules mainly based on triphenylamine moieties have already been proposed. However, there is still room for the development of more efficient and easily obtainable HTMs. Within this framework, the in silico design of four novel triphenylamine/phenothiazine-based HTMs (HTM1-4) is presented here. Their electronic and molecular properties have been investigated by means of Density Functional Theory (DFT) and Time Dependent DFT (TDDFT) methods and the results have been compared to those of Spiro-OMeTAD and a previously reported phenothiazine-based HTM (PTZ2). The analysis suggests that HTM1-4 fulfil the requirements that enable hole extraction and transport processes in PSCs. Therefore, they should be considered as possible alternatives to Spiro-OMeTAD for the construction of potentially efficient PSCs.

Low-cost and efficient hole transport materials based on 9-phenyl-9H-carbazole branch for perovskite solar cells

Hole transport materials (HTMs) play a pivotal role in the hole extraction and transportation processes in perovskite solar cells (PSCs). Although a great number of HTMs based on various planar conjugated cores have been explored, the development of branches is rather limited. In this work, branches of 9-phenyl-9H-carbazole derivatives have been incorporated in different N-alkylated dithieno[3,2-b:2′,3′-d]pyrrol (DTP) core to construct HTMs (TM-9 to TM-14). Among them, TM-13 with 9-(4-methoxyphenyl)-9H-carbazole branch exhibites excellent performance in hole extraction and transportation ability. Consequently, the PSCs based on TM-13 have achieved the power conversion efficiency (PCE) of 20.44%, which is comparable to the PCE of 20.62% with the widely used Spiro-OMeTAD HTM. More importantly, the synthetic cost of TM-13 (62 $/g) is much lower than that of Spiro-OMeTAD (400 $/g), suggesting its promising commercialization for low-cost and efficient HTMs for PSCs.

Benefitting from Synergistic Effect of Anion and Cation in Antimony Acetate for Stable CH3 NH3 PbI3 -Based Perovskite Solar Cell with Efficiency Beyond 21.

Both the film quality and the electronic properties of halide perovskites have significant influences on the photovoltaic performance of perovskite solar cells (PSCs) because both of them are closely related to the charge carrier transportation, separation, and recombination processes in PSCs. In this work, an additive engineering strategy using antimony acetate (Sb(Ac)3 ) is employed to enhance the photovoltaic performance of methylammonium lead iodide (MAPbI3 )-based PSCs by improving the film quality and optimizing the photoelectronic properties of halide perovskites. It is found that Ac- and Sb3+ of Sb(Ac)3 play different roles and their synergistic effect contributed to the eventual excellent photovoltaic performance of MAPbI3 -based PSCs with a power conversion efficiency of above 21%. The Ac- anions act as a crystal growth controller and are more involved in the improvement of perovskite film morphology. By comparison, Sb3+ cations are more involved in the optimization of the electronic structure of perovskites to tailor the energy levels of the perovskite film. Furthermore, with the assistance of Sb(Ac)3 , MAPbI3 -based PSCs deliver much improved moisture, air, and thermal stability. This work can provide scientific insights on the additive engineering for improving the efficiency and long-term stability of MAPbI3 -based PSCs, facilitating the further development of perovskite-based optoelectronics.

Ionic Liquid Additive‐Assisted Highly Efficient Electron Transport Layer‐Free Perovskite Solar Cells

Perovskite solar cells (PSCs) have achieved unprecedented power conversion efficiency improvements, and further development is stepping to industrialization. In terms of industrial manufacturing, simplifying the solar cell structure is critical in both fabrication process design and cost control. Due to the bipolar charge transport nature of perovskites, the elimination of the charge carrier transport layer is possible. Herein, EMIMPF6 ionic liquid is incorporated into the perovskite film to modulate the energy‐level alignment and the charge transfer kinetics, demonstrating a high‐performance electron transport layer‐free (ETL‐free) PSC. The integrated EMIMPF6 assisted the internal charge collection and favored the interfacial charge transfer from perovskite to FTO substrate, contributing to the high performance of ETL‐free PSCs. The ETL‐free PSCs showed a conversion efficiency of 16.2%, which is comparable with its conventional counterpart. This work provides a solution to simplify the PSC structure and would have an impact on designing a scalable manufacturing process for PSCs.