Processing Of Perovskite Solar Cells Research Articles

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.

In the Quest of Low‐Frequency Impedance Spectra of Efficient Perovskite Solar Cells

Measurement and understanding of electrochemical impedance spectroscopy of perovskite solar cells (PSCs) are nontrivial, as perovskite absorbers are a mixed conductor exhibiting both ionic and electronic motion. Moreover, the interpretation of the low‐frequency spectra especially low‐frequency resistance (R LF) is ambiguous. Some reports suggest that R LF is related to ionic transport resistance, whereas others attribute it with the recombination processes. Herein, more light is put on the quest of low‐frequency impedance spectra of efficient PSCs. It is found that high‐ and low‐frequency resistances (R HF and R LF) follow a similar dependence on the applied bias and illumination with a comparable slope. These resistances are associated with the recombination processes in PSCs. The relation between low‐frequency spectra of PSCs and the physical parameters such as the role of the interface, grains’ sizes, and perovskite composition is studied. It is found that the low‐frequency spectra of PSCs mainly depend on the grains’ sizes and shift toward the high frequency, i.e., toward faster time constants with increasing the grain size. It is observed that these devices exhibit the lower recombination and higher open‐circuit voltage. A convenient way for the in‐depth analysis of PSCs, which will be crucial for designing better‐performing PSCs, is provided.

Lead-free tin perovskite solar cells

Summary The development of efficient and stable lead-free perovskite solar cells (PSCs) is crucial for addressing the concern of environmental pollution from the toxic element lead. In recent years, tin PSCs have emerged as a promising candidate for high-performance, eco-friendly photovoltaic technology with a high certified power conversion efficiency (PCE) of more than 11%, indicating a great potential for future applications. Here, we review the recent efficiency progress of tin PSCs based on the equivalent circuit model of solar cells. We then discuss approaches toward efficiency improvement from the device viewpoint, such as optimizing the band gap, increasing the light-harvesting efficiency and carrier diffusion length, surface passivation, and regulating the interface energy-level alignment. Finally, we point out the possibility of reaching 20% PCE for tin PSCs and issues regarding enlarging the cell size and realizing scalable production in the future. We expect that these perspectives will be helpful for accelerating the commercialization of tin PSCs.

Inverted planer perovskite solar cells fabricated by all vapor phase process

A simple vapor-based fabrication process for perovskite solar cells is developed and applied to the fabrication of inverted planar CH3NH3PbI3 (MAPbI3) perovskite solar cells. In this process, PbI2 film is deposited by vacuum evaporation on the hole transport layer (HTL), followed by converting it into the MAPbI3 phase by annealing in methylammonium iodide (MAI) vapor. Using the converted MAPbI3 films, we fabricated inverted planar perovskite solar cells by vapor phase-based process with a device structure of glass/TCO/HTL/MAPbI3/C60/BCP/Ag, in which PEDOT:PSS and copper phthalocyanine (CuPc) were used as an HTL. A power conversion efficiency as high as 16.1% was obtained for the solar cell using CuPc as an HTL by a fully vapor-based process. Furthermore, we observed the improvement of the stability of the solar cells when using CuPc instead of PEDOT:PSS as an HTL.

Vacuum deposited PbI2 film grown at elevated temperatures for improved efficiency of CH3NH3PbI3 based planar perovskite solar cells

Herein, we report on the elevated temperature vacuum deposition of PbI2 film and its conversion into high-quality CH3NH3PbI3 perovskite film using a two-step vapor-solution deposition process for perovskite solar cells. The CH3NH3PbI3 perovskite films made with PbI2 layer deposited at elevated temperature possess large grain size and pinhole-free morphology, and they exhibit very high absorption and low radiative recombination. We fabricated FTO/PEDOT:PSS/CH3NH3PbI3/PCBM/Al planar perovskite solar cells using PbI2 layers deposited at different substrate temperatures. Interestingly, we observed a major improvement (∼65 %) in the power conversion efficiency of the cell using the perovskite film grown with PbI2 film deposited at 150 °C as compared to the film grown at room temperature. These devices show enhanced ambient stability compared to the case of the PbI2 layer deposited at room temperature. The origin of highly improved performance and higher stability of the devices made with elevated temperature deposition is investigated in detail.

Identification of the dominant recombination process for perovskite solar cells based on machine learning

Over the past decade, perovskite solar cells have become one of the major research interests of the photovoltaic community, and they are now on the brink of catching up with the classical inorganic solar cells, with efficiency now reaching up to 25%. However, significant improvements are still achievable by reducing recombination losses. The aim of this work is to develop a fast and easy-to-use tool to pinpoint the main losses in perovskite solar cells. We use large-scale drift-diffusion simulations to get a better understanding of the light intensity dependence of the open-circuit voltage and how it correlates to the dominant recombination process. We introduce an automated identification tool using machine learning methods to pinpoint the dominant loss using the light intensity-dependent performances as an input. The machine learning was trained using >2 million simulations and gives an accuracy of the prediction up to 82%.

Real Impacts of Ligand-Capped Nanocrystals in Perovskite Solar Cells

Perovskite solar cells (PSCs) has been reached the certified power conversion efficiency (PCE) of 25.2 % in 2019. They are having received large attention because of their superior optoelectronic properties (such as high charge carrier mobility, tunable bandgap, high absorption coefficient) and even the cost-effective process.In the latest fabrication process for high-efficiency PSCs, surface-defect engineering of perovskite film has attracted tremendous attention. Because, the control of surface-defects can play a critical role in grain boundaries of perovskite, and interfaces between perovskite and charge transport layer, leading to PSCs with further improved photovoltaic (PV) performance and long-term stability. There are many exertion for reducing surface-defects state densities of perovskite film by applying an additional passivation layer, for instance cross-linked molecules and two-dimensional (2D) materials (2D-perovskite, graphene, and MoS2) at surface of perovskite film.Most recently, perovskite nanocrystals (NCs) are being investigated as an additional layer for high-efficiency PSCs owing to anticipation of their multifunctional properties including high light-harvesting properties, efficient charge transport by carrier cascade effect, and surface passivation effect. However, it seems to remain under question whether these functions are related to the light-harvesting, suitable band alignment, and surface passivation for PSCs, due to ligand capped NCs.In this study, we investigated that the functions of NCs layer in PSCs with various NCs capped same ligand. To confirm the effects of NC layer in PSCs, we fabricated n-i-p planar devices, which follow FTO/c-TiO2/Perovskite/NC layer/Spiro-OMeTAD/Au structure with three kinds of NCs (CsPbBr3, CsPbI3, and InP). All these NCs have different electrical and optical properties, but nevertheless the devices with each NC layer showed similarly improved PV performance.In analysis results of each function of the NC layer, there were no light-harvesting effects by all NCs layer due to high absorption coefficient and sufficient thickness of perovskite film. In addition, NC layer could not work as a carrier cascade layer at the interface between the perovskite film and hole transport layer due to poor electrical properties of capping ligand. Finally, the NC layer affected only on the surface passivation of perovskite film, and furthermore we found that Oleylamine (OLA) ligand of the NCs was a major cause of the surface passivation effect. We believe that the optimization of the surface passivation effect of fatty amine ligands can further improve the PV performance of PSCs.

Easy-to-process and high-performance colorful perovskite solar cells using a multilayer planar filter.

Color-rendering manipulation of solar cells is drawing increasing interest, since the integration of color displaying can promote various advanced applications. However, the dual functionality of high-performance operation and easy processing remain a challenge. Here we propose a colorful perovskite solar cell (PSC) based on purely planar layers. The photonic crystal (PC), which does not interfere with the PSC processing, enables the display of high-purity colors and maintaining the number of PC layers at 4-6. The fabricated PSC with a four-layer PC successfully displays red-green-blue (RGB) colors, with the power-conversion efficiency of 10.94%, 11.01%, and 13.70%, respectively. Further study indicates that by employing a six-layer PC the PSC can obtain excellent color-displaying effect with the color gamut up to 81.8% of the standard RGB. It also shows that the design has a good tolerance to the deviation of layer thickness.

Fabrication and degradation performance analysis of perovskite solar cells

Methyl–ammonium lead–halide perovskites are acknowledged as highly promising materials for photovoltaic applications.The popularity of these materials is due to the high efficiency of ready photovoltaic devices comparable to the efficiency of industrial silicon solar cells as well as the possibility of significant reduction in production cost. Perovskite materials have a straight and narrow bandgap, as a result of which they have a high light absorption efficiency comparable to silicon;  and to obtain solar cells requires a thin layer of a solution obtained from solutions, which significantly reduces the production of solar cells from perovskite. The fabrication process for perovskite solar cells is rather simple and does not require high temperatures. Also, the ease of manufacturing of laboratory samples gives an opportunity to develop this technology with low capital expenditures and to join to the global research and trends in this field. The paper describes the results of fabrication and study of degradation under the influence of external factors, the atmosphere of perovskite films and solar cells obtained at a temperature of 100° C by centrifugation, which makes it possible to apply uniform films with a thickness of several nanometers to several microns easy and quickly. Key words: alternative energy, photovoltaics, perovskite solar cells.

Photoluminescence kinetics for monitoring photoinduced processes in perovskite solar cells

The research on halide perovskites is in its peak activity at the moment due to the material’s potential application in photovoltaics. It is well known that slow processes, from seconds to minutes, are very significant in perovskite films and devices as compared to conventional photovoltaic materials. The kinetics of photoluminescence (PL) is informative data for studying such processes. In particular, tracing the change in PL intensity under continuous laser excitation provides information on charge carriers’ recombination and the efficiency of their extraction from the absorber layer. Although widely available, this method was applied mainly for the research on thin films. However, monitoring PL kinetics on complete solar cells as well as on incomplete device stacks at each fabrication and lifespan stage can provide an important information on the device optimization and determination of the layers and interfaces that limit device efficiency and stability. Here, we demonstrate the advantages of the method by tracing the evolution of PL kinetics at seconds-to-minutes timescale upon: (1) varying perovskite composition (MAPbI3, Cs0.15FA0.85PbI2.7Br0.3, Cs0.05(MA0.15FA0.85)0.95PbI2.55Br0.45); (2) layer-by-layer stack construction of Cs0.15FA0.85PbI2.7Br0.3-based solar cell and (3) the device on-shelf degradation. In this way, information on charge carrier recombination, diffusion and extraction is revealed purely by optical, contactless and non-destructive means.

Role of Water in Suppressing Recombination Pathways in CH3NH3PbI3 Perovskite Solar Cells

Moisture degradation of halide perovskites is the Achilles heel of perovskite solar cells. A surprising revelation in 2014 about the beneficial effects of controlled humidity in enhancing device efficiencies overthrew established paradigms on perovskite solar cell fabrication. Despite the extensive studies on water additives in perovskite solar cell processing that followed, detailed understanding of the role of water from the photophysical perspective remains lacking; specifically, the interplay between the induced morphological effects and the intrinsic recombination pathways. Through ultrafast optical spectroscopy, we show that both the monomolecular and bimolecular recombination rate constants decrease by approximately 1 order with the addition of an optimal 1% H2O by volume in CH3NH3PbI3 as compared to the reference (without the H2O additive). Correspondingly, the trap density reduces from 4.8 × 1017 cm-3 (reference) to 3.2 × 1017 cm-3 with 1% H2O. We obtained an efficiency of 12.3% for the champion inverted CH3NH3PbI3 perovskite solar cell (1% H2O additive) as compared to the 10% efficiency for the reference cell. Increasing the H2O content further is deleterious for the device. Trace amounts of H2O afford the benefits of surface trap passivation and suppression of trap-mediated recombination, whereas higher concentrations result in a preferential dissolution of methylammonium iodide during fabrication that increases the trap density (MA vacancies). Importantly, our study reveals the effects of trace H2O additives on the photophysical properties of CH3NH3PbI3 films.

Rapid processing of perovskite solar cells through pulsed photonic annealing: a review

The performance of materials in perovskite solar cells has garnered a fair amount of interest because they are solution processable and thus a prime target for roll-to-roll coating. The precursor materials are typically prepared in solutions and deposited using common evaporative techniques, some that can be adapted to roll-to-roll manufacturing. However, there are some existing challenges that should be overcome to allow for the films to be stable in ambient conditions such that they can be deposited more cost-effectively. In this work, we report on solution engineering that enables deposition of the perovskite materials in an ambient environment using roll-to-roll applicable technologies. These engineered chemistries were also designed to enable rapid post-processing steps to limit the web length within a conventional oven. Scanning electron microscopy and X-ray diffraction analysis showed that the films achieved consistent morphology and crystallinity, and performed well in solar cell devices. Results of several chemistries and processes will be presented.

Exploiting Two‐Step Processed Mixed 2D/3D Perovskites for Bright Green Light Emitting Diodes

AbstractMixed 2D/3D perovskite films with self‐assembled quantum wells have significantly improved the performance of perovskite light emitting diodes (PeLEDs). In this work, such films are fabricated through a two‐step interdiffusion method that is widely employed in processing of perovskite solar cells, however, remains rarely explored for PeLEDs. The effects of incorporating large‐cation ligand, i.e., butylammonium bromide (BABr) into formamidinium lead bromide (FAPbBr3) based perovskites, in terms of film composition, morphology, optoelectronic properties as well as device performance are thoroughly investigated in this method. By modulating BABr:PbBr2 ratio in the precursor solution, the optimal device shows a maximum external quantum efficiency (EQE) of 7.36% at 147.7 mA cm−2 and a brightness of 37 720 Cd m−2 at 5 V. The performance is remarkably higher than a reference device without BABr that shows a maximum EQE of 2.53% and a brightness of 6190 Cd m−2 at 5 V. The versatility of this method is further extended to another large‐cation ligand, 4‐fluoro‐benzylammonium bromide (F‐BZABr), which leads to maximum EQE of 8.55%. This work indicates two‐step processed mixed 2D/3D perovskites are promising for bright green PeLEDs.

Grain boundary regulation of flexible perovskite solar cells via a polymer alloy additive

Due to the rapid processes in perovskite solar cells (PCSs), the flexible PCSs have triggered more and more attention for distributed generation. The fragility of perovskite crystals and quality of perovskite films on flexible substrate are main challenges for the further improvement. Recently, some polymer additive, such as poly(methyl methacrylate) (PMMA) assistance method for crystal growth have been widely reported. However, the fragile PMMA could not provide a desirable mechanical endurance for flexible PSCs. Here, we demonstrate a polymer alloy, which can simultaneously benefit the crystal growth and improve the flexibility. With this approach, a fully covered and compact perovskite film is achieved with a smooth surface. As a result, an enhanced efficiency of 17.54% and 14.01% for rigid and flexible PSCs is demonstrated, respectively. More importantly, the polymer alloy dramatically improves the mechanical stability of the devices, which shows a great potential for future applications in wearable electronics.

High performance of low-temperature processed perovskite solar cells based on a polyelectrolyte interfacial layer of PEI

Abstract Perovskite solar cells (PSCs) have been paid more attention because of its high power conversion efficiency (PCE) and flexible applications. Low temperature process for PSCs is critical for high performance flexible devices and industrial applications. Herein, the photovoltaic properties of the PSCs based on a polyelectrolyte interfacial layer of polyethyleneimine (PEI) were studied in this work and the configuration of PSCs was indium tin oxide (ITO)/PEI/SnO2/perovskite/spiro-OMeTAD/Ag. Due to the spin-coated PEI on ITO substrates, smooth cathodes (ITO/PEI) with low work function were obtained and the champion PCE of 19.36% and 16.81% for the rigid and flexible devices respectively was achieved accordingly. Moreover, the PCE of the rigid and flexible PSCs with PEI (0.1 mg mL−1) remained ∼95% and ∼90% of the initial values respectively after 80 days in ambient conditions. Meanwhile, the PCE of the flexible PSCs based on PEI (0.1 mg mL−1) remained 85% of the initial value after 100 bending cycles and the bendability of the flexible PSCs was improved accordingly. All the experimental data implied that the fabrication of PEI onto ITO electrodes was an effective way to promote the photovoltaic properties of the low-temperature processed rigid and flexible PSCs.

Scalable Fabrication of Perovskite Solar Cells to Meet Climate Targets

Summary Cost modeling shows that high-throughput processing of perovskite solar cells is required not only to compete with incumbent technologies in terms of levelized cost of energy, but more importantly, it is the major enabling factor facilitating sustainable growth rates of solar cell manufacturing capacity commensurate with global climate targets. We performed rapid thermal annealing at blade-coating speed to quickly deposit and convert perovskite thin films for scalable manufacturing of perovskite solar cells. In situ X-ray diffraction during film deposition and thermal conversion gave insight into the formation of crystalline intermediates, essential for high-quality films. Parameters were optimized based on the in situ study, allowing perovskite films to be annealed within 3 s with a champion power conversion efficiency of 16.8%. This opens up a clear pathway toward industrial-scale high-throughput manufacturing, which is required to fulfill the projected photovoltaic installation rates needed to reach climate goals.

All electrospray printed perovskite solar cells

The power conversion efficiencies of perovskite solar cells (PSCs) have reached 23.3% recently, rivaling those of established photovoltaic technologies. For PSCs to be commercially competitive, one of the important challenges is to overcome the limitations of small area and excessive material waste from spin-coating. Electrospray printing is a scalable and roll-to-roll compatible method with high material utilization rate. Here, we report an all electrospray printing process for PSCs in ambient air below 150 °C. Strategies for successful electrospray printing of PSCs include formulating the precursor inks with solvents of low vapor pressures and judicial choice of droplet flight time, as well as tailoring the wetting property of the substrate to suppress coffee ring effects. Implementation of these strategies leads to pin-hole free, smooth and uniform perovskite layer, hole transport layer and electron transport layer. The power conversion efficiency of the all electrospray printed devices reaches up to 15.0%, which is the highest to date for fully printed PSCs using mainstream printing methods in air without significant material waste.

The performance enhancement of HTM-free ZnO nanowire-based perovskite solar cells via low-temperature TiCl4 treatment

Charge carrier transport layer made of aligned ZnO nanowires (NW) coated with TiO2 layer via low-temperature hydrolysis process for perovskite solar cells (PSC) applications. Aligned ZnO NWs were grown by solution approach onto transparent conducting oxide substrates and treated with 25 mM of titanium tetrachloride (TiCl4). TiO2 layered ZnO NWs were composed of single crystalline, uniformly covered with amorphous TiO2 nanoparticles was characterized by scanning and transmission electron microscopy. Such TiO2 layered ZnO NW architecture, with the unique combination of high surface-area and infiltration of perovskite more into the electrode and a maximum photocurrent density (JSC) of 14.30 mA cm−2 and a power conversion efficiency (η) of 7.05% are demonstrated, which is higher than the ZnO NWs. Dark current density is decreased for TiO2 layered ZnO NW-based PSCs, due to the good interface formation between the electrode/sensitizer and it has higher energy barrier to overcome required high onset potential. TiO2 layered ZnO NWs architecture opens up a novel configuration for high-performance optoelectronic devices.

Reducing Surface Recombination by a Poly(4-vinylpyridine) Interlayer in Perovskite Solar Cells with High Open-Circuit Voltage and Efficiency.

Identifying and reducing the dominant recombination processes in perovskite solar cells is one of the major challenges for further device optimization. Here, we show that introducing a thin interlayer of poly(4-vinylpyridine) (PVP) between the perovskite film and the hole transport layer reduces nonradiative recombination. Employing such a PVP interlayer, we reach an open-circuit voltage of 1.20 V for the best devices and a stabilized efficiency of 20.7%. The beneficial effect of the PVP interlayer is proven by statistical analysis of various samples, many of those showing an open-circuit voltage larger than 1.17 V, and a 30 mV increase in average compared to unmodified samples. The reduced nonradiative recombination is proven by enhanced photo- and electroluminescence yields.