Thin-film Perovskite Solar Cells Research Articles

Infrared-reflective ultrathin-metal-film-based transparent electrode with ultralow optical loss for high efficiency in solar cells

In this work we study in-depth the antireflection and filtering properties of ultrathin-metal-film-based transparent electrodes (MTEs) integrated in thin-film solar cells. Based on numerical optimization of the MTE design and the experimental characterization of thin-film perovskite solar cell (PSC) samples, we show that reflection in the visible spectrum can be strongly suppressed, in contrast to common belief (due to the compact metal layer). The optical loss of the optimized electrode (~ 2.9%), composed of a low-resistivity metal and an insulator, is significantly lower than that of a conventional transparent conductive oxide (TCO ~ 6.3%), thanks to the very high transmission of visible light within the cell (> 91%) and low thickness (< 70 nm), whereas the reflection of infrared light (~ 70%) improves by > 370%. To assess the application potentials, integrated current density > 25 mA/cm2, power conversion efficiency > 20%, combined with vastly reduced device heat load by 177.1 W/m2 was achieved in state-of-the-art PSCs. Our study aims to set the basis for a novel interpretation of composite electrodes/structures, such as TCO–metal–TCO, dielectric–metal–dielectric or insulator–metal–insulator, and hyperbolic metamaterials, in high-efficiency optoelectronic devices, such as solar cells, semi-transparent, and concentrated systems, and other electro-optical components including smart windows, light-emitting diodes, and displays.

Modeling for Efficiency Enhancement of Perovskite Thin-Film Solar Cell by Using Double-Absorber and Buffer Layers

Perovskite solar cells appear to be the most promising candidate for thin-film solar cells. In this work, double layer Perovskite solar cells were simulated using a SCAPS-1D simulator in which different thickness of the perovskite layers was used, a buffer layer of PEDOT:PSS was used, the effect of defect density in absorbing layers, the influence of doping in Spiro-OMeTAD as well as the effect of temperature is studied. With this proposed simulated model, the maximum efficiency of the perovskite solar cell reaches 28.22%. Hence this simulation work will provide handy information in fabricating perovskite solar cells to reasonably choose material parameters and to achieve high efficiency.

Solution slot-die coating perovskite film crystalline growth observed by &lt;i&gt;in situ&lt;/i&gt; GIWAXS/GISAXS

Solution method is an important means of fabricating optoelectronic devices. During the thin film sample preparation, organic or inorganic perovskite semiconductor material usually needs to be finished in a glove box. However, most of the traditional experimental characterizations under the air environment, it is hard to reflect the reality of the structure and performance between film and device, therefore it is urgently needed to solve the microstructure evolutions of these semiconductor films based on &lt;i&gt;in situ&lt;/i&gt; real-time representation technique. In this work, we report a synchrotron-based grazing incidence wide and small-angle scattering (GIWAXS and GISAXS) &lt;i&gt;in situ&lt;/i&gt; real-time observation technique combined with a mini glove box, thereby realizing the standard glove box environment (H&lt;sub&gt;2&lt;/sub&gt;O, O&lt;sub&gt;2&lt;/sub&gt; content all reached below 1×10&lt;sup&gt;–6&lt;/sup&gt;) under remote control film spin coating or slot-die preparation and various sample post-processing. Meanwhile, this technique can real-time monitor the microstructure and morphology evolution of semiconductor film during fabrication. Based on the &lt;i&gt;in situ&lt;/i&gt; device and GIWAXS, SnO&lt;sub&gt;2&lt;/sub&gt; ETL interface induced perovskite growth crystallization process shows that CQDs additive can result in three-dimensional perovskite, with the random orientation growth changing into highly ordered vertical orientation, meanwhile can effectively restrain the low-dimensional perovskite domain formation, helping to reveal the film microstructure transformation of inner driving force and providing the perovskite device preparation process optimized with experimental and theoretical basis. The conversion efficiency of large-area fully flexible three-dimensional perovskite thin film solar cells prepared by the roll-to-roll total solution slit coating method is increased to 5.23% (the area of a single device is ~15 cm&lt;sup&gt;2&lt;/sup&gt;). Therefore, using the &lt;i&gt;in situ&lt;/i&gt; synchrotron-based glove box device, the microstructure evolution and the associated device preparation conditions of perovskite and organic semiconductor thin films can be controlled, and the thin film growth interface characteristics and film quality can be further controlled, which is the key technology to control the optimization process conditions of semiconductor thin films and devices.

Improving photoluminescence properties and reducing recombination of CsPbBr3 perovskite through lithium doping.

This study investigates the impact of lithium doping on the structural and photophysical properties of spin-coated CsPbBr3 perovskite thin films. The deposited films display a pristine structure, preferentially growing along the (220) direction, and exhibit high-quality green photoluminescence at around 530 nm. The doping leads to an improvement in the optical properties of the films, as evidenced by a stronger photoluminescence (PL) intensity compared to undoped CsPbBr3, particularly at temperatures below 200 K. The increase in PL intensity suggests a decrease in defects and surface passivation. Additionally, the decrease in the power-law exponent β from 1.6 to 1.0 indicates a reduction in non-radiative recombination, likely due to trap states filling with free electrons induced by the doping. Overall, doping with lithium reduces non-radiative recombination, fills trap states, and reduces band tail/activation energy, leading to improved optoelectronic properties of the films. This investigation provides insights into the photophysical properties of the Li-CsPbBr3 absorber layer and the recombination mechanism, and helps to unravel new methods for the development of high-stability, high-performance perovskite thin-film solar cells and optoelectronic devices.

Numerical Simulation of Lead-Free Tin and Germanium Based All Perovskite Tandem Solar Cell

The ability to customize the materials bandgaps makes perovskite solar cells a promising candidate for hybrid-tandem applications. This allows them to effectively utilize parts of the solar spectrum that silicon-based solar cells cannot efficiently capture, resulting in higher absorption coefficients. However, there is a lack of research on lead-free all-perovskite tandem solar cells, and secondary data on materials is limited. One of the main challenges in previous studies is the high cost and solid structure of traditional silicon-based solar cells, which require significant storage space. Additionally, lead-based perovskite solar cells pose environmental concerns due to their water solubility and potential harmful effects upon consumption. To address these issues, thin-film perovskite solar cells with liquid solvents are employed in the solar cell design. Lead is replaced with germanium and tin-based perovskites, which exhibit comparable photovoltaic performance to silicon. In the present work, the OghmaNano simulation tool was utilized to conduct numerical simulation of the perovskite design. The perovskite solar cell layers were structured as follows: FTO/ZnO/MAGeI3/Spiro-OMeTAD/FAMASnGeI3/Cu2O/Au. The variables considered included optimum layer thicknesses and bandgaps, as well as the most suitable materials for the ETL and HTL, aiming to obtain the highest efficiency. Based on the simulation results, the proposed perovskite structure shows remarkable photovoltaic parameters. The Voc was measured at 0.84 V Jsc of 16.1 mA/cm2, FF of 0.825, and PCE that reached 11.12%. This project contributes to future research on materials for the ETL and HTL of lead-free, tin and germanium based APTSCs.

On performance of thin-film meso-structured perovskite solar cell through experimental analysis and device simulation

In the last few years, there has been an unprecedented progress in the increase of the power conversion efficiency of perovskite solar cells. Evidently, further advances in the efficiency of these devices will depend on the constraints imposed by the optical and electronic properties of their constituents. Quite apparently during the manufacturing process of a solar cell, there is an inevitable variation in the thicknesses of various functional layers, which affects the optoelectronic characteristics of the final sample. In this work, a possible strategy of the analysis of the solar cell performance is suggested, based on statistically averaging procedure of experimental data. We present a case study, in which the optoelectronic properties of the meso-structured perovskite solar cell (with a mesoporous TiO2 layer) are analyzed within the method providing a deeper understanding of the device operation. This method enables an assessment of the overall quality of the device, pointing pathways towards the maximum efficiency design of a perovskite solar cell by material properties tuning.

Tungsten dopant incorporation for bandgap and type engineering of perovskite crystals

Organic–inorganic hybrid halide perovskites have shown to be viable semiconductor materials, as the absorber layer of solar cells. Unfortunately, the polycrystalline qualities of perovskite films result in nonuniform coverage or a high recombination rate, which weakens the photoelectric capabilities of thin films. Here, the pure and tungsten (W)-doped methylammonium lead bromide (CH3NH3PbBr3 or MAPbBr3) films are deposited to FTO-glass substrates using the sol–gel spin coating method. The W-doping causes the nucleation and crystallization processes, which then have an impact on the film’s characteristics. It is discovered that the introduction of tungsten metal significantly enhances the quality of the perovskite film, resulting in larger grain sizes, lower band gap energy, and shorter recombination lifetimes, increasing the power conversion efficiency of perovskite thin film solar cells.

Screen-Printing Technology for Scale Manufacturing of Perovskite Solar Cells.

As a key contender in the field of photovoltaics, third-generation thin-film perovskite solar cells (PSCs) have gained significant research and investment interest due to their superior power conversion efficiency (PCE) and great potential for large-scale production. For commercialization consideration, low-cost and scalable fabrication is of primary importance for PSCs, and the development of the applicable film-forming techniques that meet the above requirements plays a key role. Currently, large-area perovskite films are mainly produced by printing techniques, such as slot-die coating, inkjet printing, blade coating, and screen-printing. Among these techniques, screen printing offers a high degree of functional layer compatibility, pattern design flexibility, and large-scale ability, showing great promise. In this work, the advanced progress on applying screen-printing technology in fabricating PSCs from technique fundamentals to practical applications is presented. The fundamentals of screen-printing technique are introduced and the state-of-the-art studies on screen-printing different functional layers in PSCs and the control strategies to realize fully screen-printed PSCs are summarized. Moreover, the current challenges and opportunities faced by screen-printed perovskite devices are discussed. This work highlights the critical significance of high throughput screen-printing technology in accelerating the commercialization course of PSCs products.

Methods for improving the stability of perovskite materials and their conversion efficiency

he research on perovskite thin film solar cells has made great progress in recent years and is believed to be a material with enormous potential for development. However, problems like relatively poor stability, environmental unfriendliness and low large-area photoelectric conversion efficiency remain to solve. Its large-scale production is still a long way off. This study introduces the recent progress of the perovskite materials for perovskite solar cells and reviews the three ways of improving the stability and photoelectric conversion efficiency of perovskite materials for solar cells, including dye sensitization, doping and graphene oxidation. Diverse dyes for sensitization of perovskite materials are listed, and their mechanics are briefly introduced. The principles of how doping and graphene oxidation improve the stability and photoelectric conversion efficiency of perovskite materials are also described in this manuscript. Finally, based on those methods, suggestions for the future development of perovskite materials for solar cells are provided.

Device simulation of CH3NH3PbI3-xClx based mixed halide perovskite thin film solar cells

Perovskite solar cells are an emerging area of study in photovoltaics research due to their low cost fabrication and high efficiency. In this paper, the numerical simulation of FTO/CdS/CH3NH3PbI3-xClx/CuI/Au device performance was investigated using solar cell capacitance simulator (SCAPS-1D). Here, mixed halide perovskite, Chloride (Cl) doped methyl ammonium lead iodide (CH3NH3PbI3-xClx), is used as perovskite light absorber layer due to good thermal stability, film quality and tunable bandgap property. In this present solar cell configuration CdS is used as buffer layer and CuI as hole transport layer (HTL). The effect of absorber layer thickness, operating temperature and different HTL’s were also analyzed on device performance. By varying the thickness of the absorber layer from 0.1 to 1.0 µm,the optimum thickness was found at 0.7 µm. In addition to this different HTL’s CuI, Spiro-OMeTAD and Cu2O were used in simulation and CuI gives best results compared to others. With optimized parameters, the proposed device achieves a PCE of 27.19%, FF of 87.88%, JSC of 23.86 mA/cm2 and VOC of 1.29 V. These optimized results will be used for the fabrication of an CH3NH3PbI3-xClx perovskite thin film solar cell.

Towards High-Efficiency Photon Trapping in Thin-Film Perovskite Solar Cells Using Etched Fractal Metadevices.

Reflective loss is one of the main factors contributing to power conversion efficiency limitation in thin-film perovskite solar cells. This issue has been tackled through several approaches, such as anti-reflective coatings, surface texturing, or superficial light-trapping metastructures. We report detailed simulation-based investigations on the photon trapping capabilities of a standard Methylammonium Lead Iodide (MAPbI3) solar cell, with its top layer conveniently designed as a fractal metadevice, to reach a reflection value R<0.1 in the visible domain. Our results show that, under certain architecture configurations, reflection values below 0.1 are obtained throughout the visible domain. This represents a net improvement when compared to the 0.25 reflection yielded by a reference MAPbI3 having a plane surface, under identical simulation conditions. We also present the minimum architectural requirements of the metadevice by comparing it to simpler structures of the same family and performing a comparative study. Furthermore, the designed metadevice presents low power dissipation and exhibits approximately similar behavior regardless of the incident polarization angle. As a result, the proposed system is a viable candidate for being a standard requirement in obtaining high-efficiency perovskite solar cells.

The surface chemistry of ionic liquid-treated CsPbBr3 quantum dots.

The power conversion efficiencies of lead halide perovskite thin film solar cells have surged in the short time since their inception. Compounds, such as ionic liquids (ILs), have been explored as chemical additives and interface modifiers in perovskite solar cells, contributing to the rapid increase in cell efficiencies. However, due to the small surface area-to-volume ratio of the large grained polycrystalline halide perovskite films, an atomistic understanding of the interaction between ILs and perovskite surfaces is limited. Here, we use quantum dots (QDs) to study the coordinative surface interaction between phosphonium-based ILs and CsPbBr3. When native oleylammonium oleate ligands are exchanged off the QD surface with the phosphonium cation as well as the IL anion, a threefold increase in photoluminescent quantum yield of as-synthesized QDs is observed. The CsPbBr3 QD structure, shape, and size remain unchanged after ligand exchange, indicating only a surface ligand interaction at approximately equimolar additions of the IL. Increased concentrations of the IL lead to a disadvantageous phase change and a concomitant decrease in photoluminescent quantum yields. Valuable information regarding the coordinative interaction between certain ILs and lead halide perovskites has been elucidated and can be used for informed pairing of beneficial combinations of IL cations and anions.

Improved Optical Efficiencies of Perovskite Thin Film Solar Cells by Randomly Distributed Ag Nanoparticles

Improved Optical Efficiencies of Perovskite Thin Film Solar Cells by Randomly Distributed Ag Nanoparticles

Multilayer conformal structural perovskite solar cells design for light trapping enhancement

Thin film perovskite solar cells (PSCs) have insufficient light utilization due to thickness limitation. Structural design of thin film PSCs can effectively enhance the property of light trapping and thereby improve the photocurrent density. In this work, both the thickness of perovskite layer and front Indium Tin Oxides (ITO) layer for classical PSCs was firstly optimized. 22.4% of light absorption enhancement can be achieved. Then, we proposed four different types of multilayer conformal structures PSCs consisting of hemisphere, cylinder, inverted pyramid and cone structures. Compared with the planner PSCs, the optimized hemispherical multilayer conformal structure (HMCS) PSCs can further enhance the light absorption by 12.3% and obtain the highest photocurrent density of 23.82 mA/cm−2. The photonic interaction between the structure and incident wavelength is examined and discussed. The presented method and multilayer conformal structures can be used to design the light absorption enhancement for a variety of PSCs.

Efficient thin-film perovskite solar cells from a two-step sintering of nanocrystals.

Creating semiconductor thin films from sintering of colloidal nanocrystals (NCs) represents a very important technology for high throughput and low cost thin-film photovoltaics. Here we report the creation of all-inorganic cesium lead bromide (CsPbBr3) polycrystalline films with grain size exceeding 1 μm from the bottom up by sintering of CsPbBr3 NCs terminated with short and low-boiling-point alky ligands that are ideal for use in sintered photovoltaics. The grain growth behavior during the sintering process was carefully investigated and correlated to the solar cell performance. To achieve precise control over the microstructural development we propose a facile two-step sintering process involving the grain growth via coarsening at a relative low temperature followed by densification at a high temperature. Compared with the one-step sintering, the two-step process yields a more uniform CsPbBr3 bulk film with larger grain size, higher density and lower trap density. Consequently, the photovoltaic device based on the two-step sintering process demonstrates a significant enhancement of efficiency with reduced hysteresis that approaches the best reported CsPbBr3 solar cells using a similar configuration. Our study specifies a rarely addressed perspective concerning the sintering mechanism of perovskite NCs and should contribute to the development of high-performance bulk perovskite devices based on the building blocks of perovskite NCs.

Impact of humidity in triple cation perovskite solar cells: Surface analysis

Perovskite (PVSK) is widely used in the absorber layer of solar cells due to its excellent conversion efficiency; however, these devices are highly susceptible to humidity. Furthermore, the mechanism underlying the moisture-induced performance degradation in triple cation PVSK has yet to be elucidated. In the current study, we used the anti-solvent method to prepare triple cation PVSK films in order to study the growth mechanism and influence of moisture on conversion performance. We determined that an appropriate quantity of moisture in PVSK films can improve grain growth of PVSK and increase the difference in potential energy between grain and grain boundary, thereby facilitating the transport and collection of carriers across grain boundaries. Excess moisture entering PVSK thin films leads to degradation of the PVSK absorber layer, resulting in the formation of PbI2, PbBr2, HI, FAI, and MABr, while leaving holes in the surface, which can compromise the stability of the crystals and efficiency of the solar cell. In the current study, the efficiency of PVSK thin film solar cells was 19.14% under an optimal humidity level 25%, which resulted in photoelectric characteristics and device efficiency on par with the results obtained under a pure nitrogen environment.

Study of Lead-Free Perovskite Photoelectric Devices with TiO2 as a Buffer Layer

In this work, a titanium oxide buffer layer was explored as a possible buffer electron transporting layer (ETL) with iodine-tin-based perovskite material for enhancement of a thin-film lead-free perovskite solar cell. The open-circuit voltage of the device was used as an indicator for the interface energy barrier’s change with the thickness of the TiO2. The buffer and photoabsorbing layers were deposited by vacuum reactive sputtering and a low-temperature ion-assisted process from a confocal sintered source, respectively, allowing precise tuning of the film properties and reproducibility of the solar cell behavior. The surface roughness of the buffer layers was investigated by atomic force microscopy and together with the measured absorbance spectra conclusions about the optical losses in the device were made. It was found that the highest voltage was generated from the structure with 75 nm-thick ETL. The electrical behavior of the cell with this buffer layer was additionally studied by impedance measurements. Small interface capacitance and contact resistance were obtained and considered suitable for photodetector fabrication. The practical applicability of the structure with a dual function of self-powered photodetection was demonstrated by the measurement of the response time.

Probing Charge Generation Efficiency in Thin-Film Solar Cells by Integral-Mode Transient Charge Extraction.

The photogeneration of free charges in light-harvesting devices is a multistep process, which can be challenging to probe due to the complexity of contributing energetic states and the competitive character of different driving mechanisms. In this contribution, we advance a technique, integral-mode transient charge extraction (ITCE), to probe these processes in thin-film solar cells. ITCE combines capacitance measurements with the integral-mode time-of-flight method in the low intensity regime of sandwich-type thin-film devices and allows for the sensitive determination of photogenerated charge-carrier densities. We verify the theoretical framework of our method by drift-diffusion simulations and demonstrate the applicability of ITCE to organic and perovskite semiconductor-based thin-film solar cells. Furthermore, we examine the field dependence of charge generation efficiency and find our ITCE results to be in excellent agreement with those obtained via time-delayed collection field measurements conducted on the same devices.

How do gold nanoparticles boost the performance of perovskite solar cells?

To achieve large-scale commercialization of perovskite thin-film solar cells in the near future, improving perovskite thin-films quality and properties is becoming more and more critical. We focus here on the effect of introducing gold nanoparticles (Au_NPs) in MAPbI3 layers for solar cells. Experimentally, we show a 12% improvement of the stabilized efficiency by introducing an optimized amount of Au_NPs. The nanoparticles action has been addressed through a combination of experiments and optical simulations. First, we have calculated Mie absorption coefficients, done numerical FDTD simulations and transfer-matrix simulations to model the localized surface plasmon resonance (LSPR) and light scattering efficiency of Au_NPs. They have allowed us to state that, to reach a significant beneficial effect, the nanoparticle volume ratio must be above 1%, which is far above the content in our optimized perovskite solar cells layers. Only a negligible enhancement of light absorption can be attributed to the Au_NPs. Secondly, by combining several analysis techniques, especially by using glow discharge-optical emission spectroscopy (GD-OES), we reveal the mechanism of how Au_NPs improve the quality of perovskite films. The gold nanoparticles lead to the formation of monolithic grains with few defects and reduced grain boundaries which are the targeted properties for high efficiency. Therefore, in our devices, the effect of Au_NPs on the improvement of the quality of the perovskite layer is far more significant than that of the increase in light-harvesting. Finally, further performance and stability increases have been achieved by introducing the treatment of Au_NPs/MAPbI3 film surface by n-propylammonium iodide (PAI). It resulted in a power conversion efficiency of over 20%.

Laminated high-performance semi-transparent perovsktie solar cells: Enabled by sticky polyethyleminine as glue

Electric glue plays a key role in laminating top electrodes for organic and perovskite thin-film solar cells. However, there has been seldom reported for chemically reactive low–work function electrode yet. In this paper, polyethyleneimine (PEI) was developed as transparent top electrode adhesive, surface modifier for air-stable low–work function, and barrier to suppress the chemical corrosion of metal electrode in perovskite solar cells. The lamination was finished under room temperature with a pressure as low as 8 MPa, which is a very mild condition for device fabrication. The solar cells with transparent top electrode laminated for 10min had the best performances, in which the average value of PEI thickness between silver nanowires and the adjacent layer was found to play a key role in adjusting the performance of solar cells.