Efficient Flexible Perovskite Solar Cells Research Articles

Green Anti-solvent Processed Efficient Flexible Perovskite Solar Cells

Flexible perovskite solar cells (PSCs) possess compatible features with low-cost, high throughput production approaches, showing great potentials in wearable, portable, flyable, and deployable applications. However, flexible PSCs with superior efficiency are commonly fabricated with an anti-solvent assisted crystallization (ASAC) method, which uses highly toxic solvents as the processed solvents. In this work, we use environmentally benign anti-solvents for the fabrication of flexible PSCs. Benefiting from the low-temperature solution processability of a high quality SnO2 electron transport layer (ETL) with superior electron extraction and transfer features, flexible PSCs show an impressive PCE over 17% under reverse scan. This, to the best of our knowledge, is among the highest performances for flexible PSCs and is the first report for flexible PSCs fabricated by green anti-solvent processed techniques. These results provide new opportunities for environmental-friendly manufacturing of high performance f...

Efficient, hysteresis free, inverted planar flexible perovskite solar cellsviaperovskite engineering and stability in cylindrical encapsulation

Efficient flexible perovskite solar cells were obtained by compositional engineering. Cylindrically encapsulated devices retained 90% of the device efficiency after 6000 h.

Room-temperature synthesized SnO2 electron transport layers for efficient perovskite solar cells.

Tin oxide (SnO2) is widely used as electron transport layer (ETL) material in perovskite solar cells (PSCs). Numerous synthesis methods for SnO2 have been reported, but they all require a proper thermal treatment for the SnO2 ETLs. Herein we present a simple method to synthesize SnO2 nanoparticles (NPs) at room temperature. By using butyl acetate as a precipitator and a proper UV–Ozone treatment to remove Cl residuals, excellent SnO2 ETLs were obtained without any thermal annealing. The highest power conversion efficiency (PCE) of the prepared PSCs was 19.22% for reverse scan (RS) and 18.79% for forward scan (FS). Furthermore, flexible PSCs were fabricated with high PCEs of 15.27%/14.74% (RS/FS). The low energy consuming SnO2 ETLs therefore show great promise for the flexible PSCs' commercialization.

Tailored lead iodide growth for efficient flexible perovskite solar cells and thin-film tandem devices

Flexible perovskite solar cells (PSCs) hold great promise for the low-cost roll-to-roll production of lightweight single- and multijunction photovoltaic devices. Among the different deposition methods used for the perovskite absorber, the two-step hybrid vacuum-solution approach enables precise control over the thickness and morphology of PbI2. However, efficient conversion to perovskite is limited by diffusion of the organic cations in the compact lead halide layer. Herein, a multistage absorber deposition is developed by thermal evaporation of PbI2 and spin coating of CH3NH3I (MAI). The process relies on the different types of growth of vacuum-deposited PbI2 onto amorphous and crystalline surfaces. This approach represents a way to effectively increase the absorber thickness while tackling the limited MAI diffusion in the compact PbI2 film via a two-step deposition method. The efficiency of flexible PSCs is improved from 14.2 to 15.8% with multistage deposition. Furthermore, the use of an amorphous transparent conductive oxide (TCO), InZnO, enhances the mechanical resistance against bending with respect to conventional crystalline TCO-based flexible devices. Near-infrared transparent flexible PSCs are developed with an efficiency of 14.0% and average transmittance of ~74% between 800 and 1000 nm. Flexible perovskite/CIGS thin-film tandem devices are demonstrated with an efficiency of 19.6% measured in the four-terminal configuration.

Flexible and Biocompatibility Power Source for Electronics: A Cellulose Paper Based Hole‐Transport‐Materials‐Free Perovskite Solar Cell

Flexible, biocompatible, and light‐weight power sources are urgently required due to their promising application in wearable electronics. Organic‐inorganic hybrid lead halide perovskite solar cells (PSCs) with their impressive efficiency and scalable processing capability have emerged as promising candidates for efficient and reliable power sources for wearable electronics. However, the progress in developing low‐cost and efficient flexible PSCs has been confined to Poly(ethylene terephthalate) or metal foil substrates and difficulty to design PSCs on other easily accessible low‐cost substrates such as cellulose paper. Herein, the authors report the hole transport material (HTM)‐free flexible PSCs fabricated on abundant, low‐cost, and biocompatible cellulose paper substrate for the first time. The highest PCE of 9.05% for the paper based flexible HTM‐free PSC is achieved and the device could maintain over 75% of its initial PCE after 1000 bending cycles, demonstrating good stability against bending deformation. Our findings provide an avenue to fabricate reliable power source for wearable electronics.

Efficient fully laser-patterned flexible perovskite modules and solar cells based on low-temperature solution-processed SnO2/mesoporous-TiO2 electron transport layers

Efficient flexible perovskite solar cells and modules were developed using a combination of SnO2 and mesoporous-TiO2 as a fully solution-processed electron transport layer (ETL). Cells using such ETLs delivered a maximum power conversion efficiency (PCE) of 14.8%, which was 30% higher than the PCE of cells with only SnO2 as the ETL. The presence of a mesoporous TiO2 scaffold layer over SnO2 led to higher rectification ratios, lower series resistances, and higher shunt resistances. The cells were also evaluated under 200 and 400 lx artificial indoor illumination and found to deliver maximum power densities of 9.77 μW/cm2 (estimated PCE of 12.8%) and 19.2 μW/cm2 (estimated PCE of 13.3%), respectively, representing the highest values among flexible photovoltaic technologies reported so far. Furthermore, for the first time, a fully laser-patterned flexible perovskite module was fabricated using a complete three-step laser scribing procedure (P1, P2, P3) with a PCE of 8.8% over an active area of 12 cm2 under an illumination of 1 sun.

Electrochemical photocurrent enhancement in a ZnO-perovskite heterojunction using piezoelectric effect

ZnO is a candidate material to be used as the electron transport layer in flexible perovskite solar cells. However, the energy structure at the ZnO-perovskite heterojunction introduces an energy barrier affecting the photocurrent in a device. Here, we report on enhancing the photocurrent in a zinc oxide nanowire (NW)-perovskite heterojunction by employing the piezoelectric effect in NWs. The heterojunction was fabricated on an indium tin oxide coated flexible substrate. The effect of the piezoelectric charges on the photoelectric response of the heterojunction was studied in an electrochemical cell under different bending curvatures of the substrate. Employing piezoelectric effect, the photocurrent of the sample was increased by 46% from the flat state to the maximum outward curvature of 1.02 cm−1. Scanning electron microscopy (SEM), X-ray diffraction (XRD), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were performed to characterize the sample. The EIS study was performed for a sample at flat and bent states in both dark and light conditions. Based on the results an equivalent circuit model was suggested. Change in the values of the components in the model was analyzed for both the photovoltaic and piezoelectric effects in the heterojunction. This study suggests a simple approach for fabrication of efficient flexible perovskite solar cells.

Importance of ligands on TiO2 nanocrystals for perovskite solar cells**Project supported by the National Natural Science Foundation of China (Grant Nos. 51622201, 61571015, and 91433102).

The fabrication of high-quality electron-selective layers at low temperature is a prerequisite to realizing efficient flexible and tandem perovskite solar cells (PSCs). A colloidal-quantum-dot ink that contains TiO2 nanocrystals enables the deposition of a flat film with matched energy level for PSCs; however, the selection of ligands on the TiO2 surface is still unexplored. Here, we systematically studied the effect of the titanium diisopropoxide bis(acetylacetonate) (TiAc2) ligand on the performance of PSCs with a planar n–i–p architecture. We prepared TiO2 nanocrystals from TiCl4 and ethyl alcohol with Cl− ligands attached on its surface and we found that a tiny amount of TiAc2 treatment of as-prepared TiO2 nanocrystals in a mixed solution of chloroform and methyl alcohol can enhance PSC power conversion efficiency (PCE) from 14.7% to 18.3%. To investigate the effect of TiAc2 ligand on PSCs, TiO2 samples with different TiAc2 content were prepared by adding TiAc2 into the as-obtained TiO2 nanocrystal solution. We use x-ray photoelectron spectroscopy to identify the content of Cl so as to reveal that Cl ligands can be substituted by TiAc2. We speculate that the improvement in PCE originates from amorphous TiO2 formation on the TiO2 nanocrystal surface, whereby a single-molecule layer of amorphous TiO2 facilitates charge transfer between the perovskite film and the TiO2 electronic transport layer, but excessive TiAc2 lowers the PSC performance dramatically. We further prove our hypothesis by x-ray diffraction measurements. We believe the PCE of PSCs can be further improved by carefully choosing the type and changing the content of surface ligands on TiO2 nanocrystal.

Water Vapor Treatment of Low-Temperature Deposited SnO2 Electron Selective Layers for Efficient Flexible Perovskite Solar Cells

Tin oxide (SnO2) electron selective layers (ESLs) processed by low-temperature plasma-enhanced atomic layer deposition (PEALD) hold promise for fabricating lightweight and efficient flexible lead halide perovskite solar cells (PVSCs). However, the as-synthesized SnO2 ESLs typically lead to flexible PVSCs with lower open-circuit voltage (VOC) and fill factor (FF) as well as a higher degree of current density–voltage (J–V) hysteresis, compared to PVSCs fabricated on rigid substrates. Here, we report that facile water vapor treatment of PEALD-synthesized SnO2 ESLs can effectively improve the VOC and FF while reducing the degree of J–V hysteresis. The improvement in device performance is mainly attributed to the improved conductivity and electrical mobility of SnO2 ESLs enabled by water vapor treatment. With such treatment, our best flexible PVSC fabricated on a commercial substrate shows a power conversion efficiency of 18.36 (17.12)% when measured under a reverse (forward) voltage scan and a stabilized effi...

Tailoring morphology and thickness of perovskite layer for flexible perovskite solar cells on plastics: The role of CH3NH3I concentration

A smooth perovskite film fully covering the substrate is of importance for flexible perovskite solar cells (PSCs). In this study, efficient flexible PSCs are fabricated onto conductive plastic substrate by a two-step coating method under ambient condition. By adjusting the concentration of precursor CH3NH3I (MAI), the morphology and thickness of perovskite layer is effectively tailored, according to SEM and AFM analysis, which consequently gives rise to a thin perovskite layer with smooth surface and smaller grain size. As a result, flexible PSCs with efficiency of 12.7% are prepared under ambient condition, and the excellent mechanical stability of flexible PSCs is also demonstrated with bending test under severe conditions.

W(Nb)Ox-based efficient flexible perovskite solar cells: From material optimization to working principle

Flexible perovskite solar cell (PSC) using plastic substrate is one of the most focal points in the studies of thin-film solar cells. Low-temperature preparation of suitable electron selective layer (ESL) is the key issue in the fabrication of flexible PSCs. In this work, amorphous niobium-modified tungsten oxide W(Nb)Ox was prepared as ESL for efficient flexible PSC. Modification using Nb5+ improved the electron transport of WOx-based ESL by enhancing donor density, reducing interfacial depletion width, and minimizing trap states in the ESL. Consequently, photovoltaic performance of the simple planar flexible PSCs was improved, and high PCEs of 15.65% and 13.14% were obtained when ESLs were fabricated at 120°C and room temperature, respectively. In addition, the effect of ESL thickness on the hysteresis behavior of PSCs was carefully analyzed. A capacitance CE across the ESL in the ITO/ESL/perovskite structure was proposed. This capacitance could well indicate the effect of ESL thickness on hysteresis behavior. The proposed modification strategy and mechanism is expected to facilitate the development of novel and advanced functional materials.

Pinhole-Free and Surface-Nanostructured NiOx Film by Room-Temperature Solution Process for High-Performance Flexible Perovskite Solar Cells with Good Stability and Reproducibility.

Recently, researchers have focused on the design of highly efficient flexible perovskite solar cells (PVSCs), which enables the implementation of portable and roll-to-roll fabrication in large scale. While NiOx is a promising material for hole transport layer (HTL) candidate for fabricating efficient PVSCs on a rigid substrate, the reported NiOx HTLs are formed using different multistep treatments (such as 300-500 °C annealing, O2-plasma, UVO, etc.), which hinders the development of flexible PVSCs based on NiOx. Meanwhile, the features of nanostructured morphology and flawless film quality are very important for the film to function as highly effective HTL of PVSCs. However, it is difficult to have the two features coexist natively, particularly in a solution process that flawless film will usually come with smooth morphology. Here, we demonstrate the flawless and surface-nanostructured NiOx film from a simple and controllable room-temperature solution process for achieving high performance flexible PVSCs with good stability and reproducibility. The power conversion efficiency (PCE) can reaches a promising value of 14.53% with no obvious hysteresis (and a high PCE of 17.60% for PVSC on ITO glass). Furthermore, the NiOx-based PVSCs show markedly improved air stability. Regarding the performance improvement, the flawless and surface-nanostructured NiOx film can make the interfacial recombination and monomolecular Shockley-Read-Hall recombination of PVSC reduce. In addition, the formation of an intimate junction of large interfacial area at NiOx film/the perovskite layer improve the hole extraction and thus PVSC performances. This work contributes to the evolution of flexible PVSCs with simple fabrication process and high device performances.

Highly Efficient Flexible Perovskite Solar Cells with Antireflection and Self-Cleaning Nanostructures.

Flexible thin film solar cells have attracted a great deal of attention as mobile power sources and key components for building-integrated photovoltaics, due to their light weight and flexible features in addition to compatibility with low-cost roll-to-roll fabrication processes. Among many thin film materials, organometallic perovskite materials are emerging as highly promising candidates for high efficiency thin film photovoltaics; however, the performance, scalability, and reliability of the flexible perovskite solar cells still have large room to improve. Herein, we report highly efficient, flexible perovskite solar cells fabricated on ultrathin flexible glasses. In such a device structure, the flexible glass substrate is highly transparent and robust, with low thermal expansion coefficient, and perovskite thin film was deposited with a thermal evaporation method that showed large-scale uniformity. In addition, a nanocone array antireflection film was attached to the front side of the glass substrate in order to improve the optical transmittance and to achieve a water-repelling effect at the same time. It was found that the fabricated solar cells have reasonable bendability, with 96% of the initial value remaining after 200 bending cycles, and the power conversion efficiency was improved from 12.06 to 13.14% by using the antireflection film, which also demonstrated excellent superhydrophobicity.