Single-junction Perovskite Solar Cells Research Articles

Research progress of wide bandgap perovskite materials and solar cells

Organic-inorganic metal halide perovskites are a new type of photovoltaic material, they have attracted wide attention and made excellent progress in recent years. The power conversion efficiency of a single-junction perovskite solar cell has been increased to 25.2% just within a decade. Meanwhile, crystalline silicon solar cells account for nearly 90% of industrialized solar cells and have a maximum efficiency of 26.7%, approaching to their theoretical limit. It is more difficult to further improve the efficiency of single junction solar cells. It has been shown that multi-junction tandem solar cells prepared by stacking absorption layers with different bandgaps can better use sunlight, which is one of the most promising strategies to break the efficiency limitation of single-junction solar cells. Due to the bandgap tunability and low-temperature solution processability, perovskites stand out among many other materials for manufacturing multi-junction tandem solar cells. Wide bandgap perovskites with a bandgap of 1.63 eV or above have been combined with narrow band gap inorganic absorption layers such as silicon, copper indium gallium selenide, cadmium telluride or narrow bandgap perovskite to produce high efficiency tandem solar cells. In addition to the promoting of the efficiency improvement of solar cells, the wide bandgap perovskites have broad applications in photovoltaic building integration and photocatalytic fields. Therefore, it is very important to explore and develop high quality wide bandgap perovskite materials and solar cells. Unfortunately, the wide bandgap perovskites have several intrinsic weaknesses, including being more vulnerable to the migration of halogen ions under being illuminated, more defects, and greater possibility of energy level mismatching with the charge transport layers than the narrow bandgap counterparts, which limits the further development of the wide bandgap perovskite solar cells. In this review, the development status of wide bandgap perovskite solar cells is summarized and corresponding strategies for improving their performance are put forward. Furthermore, some personal views on the future development of wide bandgap perovskite solar cells are also presented here in this paper.

Two‐terminal Perovskite silicon tandem solar cells with a high‐Bandgap Perovskite absorber enabling voltages over 1.8 V

AbstractPerovskite silicon tandem solar cells are a promising technology to overcome the efficiency limit of silicon solar cells. Although highest tandem efficiencies have been reported for the inverted p‐i‐n structure, high‐efficiency single junction perovskite solar cells are mostly fabricated in the regular n‐i‐p architecture. In this work, regular n‐i‐p perovskite solar cells with a high‐bandgap mixed cation mixed halide absorber suitable for tandem solar cells are investigated by compositional engineering and the open‐circuit voltage is improved to over 1.12 V using a passivating electron contact. The optimized perovskite solar cell is used as a top cell in a monolithic perovskite silicon tandem device with a silicon heterojunction bottom cell allowing for voltages up to 0.725 V. The tandem solar cells with an active area of 0.25 cm2 achieve record open‐circuit voltages of up to 1.85 V and have efficiencies over 20%. Analyzing the perovskite absorber by spatially resolved photoluminescence measurements shows a homogenous and stable emission at ~ 1.7 eV which is an optimal value for tandem applications with silicon. The tandem solar cells are mainly limited due to a low current. A spectrometric characterization reveals that the perovskite solar cell is current limiting which could be improved by a thicker perovskite absorber.

High Short-Circuit Current Density via Integrating the Perovskite and Ternary Organic Bulk Heterojunction

We demonstrate a record short-circuit current density (28.06 mA/cm2) in a single-junction perovskite solar cell with a 1.6 eV bandgap absorber. We achieve this by integrating a ternary organic bulk heterojunction structure into a perovskite top layer to extend the photoresponse to the near-infrared region.

The Role of Surface Passivation Layer Preparation on Crystallization and Optoelectronic Performance of Hybrid Evaporated-Spincoated Perovskite Solar Cells

The main advantages of the organic–inorganic halide perovskite solar cell technology are high efficiencies achieved after short development time in combination with rather simple solution-based processing. In this paper, we address remaining challenges by presenting a low-temperature two-step hybrid evaporation-spincoating method that combines high reproducibility with easy fabrication and high stabilized efficiencies, which is compatible with the processing of pervoskite silicon tandem solar cells and avoids using hazardous solvents such as dimethylformamide and dimethylsulfoxide. Lead iodide (PbI2) is thermally evaporated and subsequently converted into a compact crystalline perovskite layer by methylammonium iodide spincoating. Moreover, the role of the interface passivation between perovskite absorber and electron transport layer on crystallization and optoelectronic properties of the perovskite absorber is investigated within a systematic thickness and concentration variation of [6, 6]-phenyl-C61-butyric acid methyl ester passivation layer and by analyzing charge extraction with spatial and time resolved photoluminescence measurements. With an optimized charge extraction, 18.2% stabilized efficiency under one sun illumination is achieved. This is the highest value reported so far for the single junction perovskite solar cells made by a two-step hybrid evaporation-spincoating method.

Back-Contact Perovskite Solar Cells

Interdigitated back-contact (IBC) architectures are the best performing technology in crystalline Si (c-Si) photovoltaics (PV). Although single junction perovskite solar cells have now surpassed 23% efficiency, most of the research has mainly focussed on planar and mesostructured architectures. The number of studies involving IBC devices is still limited and the proposed architectures are unfeasible for large scale manufacturing. Here we discuss the importance of IBC solar cells as a powerful tool for investigating the fundamental working mechanisms of perovskite materials. We show a detailed fabrication protocol for IBC perovskite devices that does not involve photolithography and metal evaporation. The interview is available at https://youtu.be/nvuNC29TvOY.

Inorganic Materials as Hole Selective Contacts and Intermediate Tunnel Junction Layer for Monolithic Perovskite‐CIGSe Tandem Solar Cells

AbstractIn order to surpass the theoretical limitation defined by the Shockley–Queisser equation for photovoltaic solar cells, multijunction devices are needed. Monolithic perovskite‐Cu(In, Ga)(Se, S)2 (CIGSe) tandem solar cells have recently become a hot research topic in photovoltaics because of the emergence of perovskite solar cells with high power conversion efficiency and the development of thin film chalcopyrite CIGSe solar cells with tunable bandgap and low cost manufacturing processes. In this review, some p‐type wide bandgap semiconductors are investigated as intermediate inorganic hole transport materials (IIHTM) and components of a tunnel junction in monolithic perovskite‐CIGSe tandem solar cells, which meet the requirements of band alignment and low‐temperature deposition process. The authors focus on designing a tandem configuration including band alignment, current matching, and optical management, describing some potential candidates of IIHTM owing to their successful implementation in single junction perovskite solar cells and the possibility of application in intermediate layers for tandem devices. Recent progress in the development of inorganic hole conductors is highlighted, and also some of the authors' work on IIHTM and their applications are presented. Finally, future research directions for IIHTM layers and monolithic perovskite‐CIGSe tandem solar cells are presented, with an aim to achieve higher photovoltaic performance than current devices.

Cost Analysis of Perovskite Tandem Photovoltaics

Summary Recently, metal halide perovskite photovoltaics (PV) are marching toward commercialization. The possibility for perovskite absorbers to be incorporated into multi-junction solar cells is also being discussed, which suggests alternative market entry. Although intensive investigations are being made on their technical feasibility, serious analysis on the cost of perovskite-based tandem modules is lacking. The levelized cost of electricity (LCOE) of solar modules is often used to evaluate technoeconomic competitiveness. Here, we performed a detailed cost analysis on two perovskite-based tandem modules (the perovskite/c-silicon and the perovskite/perovskite tandem module) compared with standard multi-crystalline silicon and single-junction perovskite solar cells. We found that perovskite PVs (both single junction and multi-junction) are competitive in the context of LCOE if the module lifetime is comparable with that of c-silicon solar cells. This encourages further efforts to push perovskite tandem modules onto the market in the future.

Quality management of high-efficiency planar heterojunction organic-inorganic hybrid perovskite solar cells

The energy extracted from solar radiation is the most abundant and accessible source of renewable energy, which will become progressively more important as time goes on. Solar cells are regarded as one of the most promising candidates for generating renewable clean energy. Recently, a new class of semiconducting material called organic-inorganic halide perovskite has received great attention of academia, and the record power conversion efficiency (PCE) of perovskite solar cell (PSC) rapidly increased from 3.8% in 2009 to 22.7% in late 2017 through intensive research due to some advantages as follows. 1) Excellent optoelectronic property. Perovskite materials exhibit excellent properties, including long diffusion length, high carrier mobility, and high absorption coefficient. 2) Low cost. The ingredients of perovskite materials are cheap, and PSCs can be manufactured by a solution process. 3) Tunable bandgap. Perovskite materials have highly tunable bandgap (1.2-2.2 eV), contributing to the further improvement in PCE of single junction PSCs by realizing the ideal bandgap (1.3-1.4 eV) as demonstrated by the Shockley-Queisser detailed balanced calculation. The basic architectures of PSCs are divided mainly into mesoscopic and planar heterojunction structures. Compared with the former configuration, the later configuration combined with low-temperature processable interlayers provides a method of fabricating flexible PSCs and tandem PSCs. Furthermore, the nonuse of the mesoscopic structure simplifies the structure of PSCs and reduces the cost and time of fabrication. The key requirement to achieve an efficient and reproducible planar heterojunction PSCs is that the perovskite layer should be uniform, continuous, and pinhole free to minimize shunting pathways. So, significant research effort is being devoted to the quality management of perovskite films with the goal of achieving the controllable preparation, including the optimization of their morphology (uniformity, coverage, roughness) and microstructure (grain size/distribution, texture), and the elimination of defects (voids, pinholes, grain boundaries), which influence the PSC performance directly. Especially for the one-step solution coating method, the film quality of perovskite on different planar substrates under varied deposition conditions exhibits a large difference, due to the complex crystallization process and the heightened sensitivity to environmental conditions. In this paper, the characteristics of perovskite materials, the nucleation-growth mechanism of films in the one-step solution method, and the evolution of cell structures are described briefly. The latest quality control methods of high-quality perovskite films prepared by solution method are then discussed emphatically. Finally, to provide references for the future research, the development and existing problems of PSCs are addressed and prospected.

Control of Electrical Potential Distribution for High-Performance Perovskite Solar Cells

Summary The electrical potential distribution within photovoltaic devices plays critical roles in governing charge carrier dynamics and the device performance. Here we present the electrical potential distribution within highly efficient perovskite solar cells (PSCs) in working status. We found the major potential drop existing at the perovskite/mesoporous TiO 2 interface, indicating one diode junction in mesoporous PSCs. In contrast, the major potential drop was found on both sides of the perovskite layer in planar PSCs, exhibiting two diode junctions where the charge carriers could be recombined more easily than single-junction PSCs. We further controlled the position of diode junctions in planar PSCs by changing the dopant concentration. The undesirable charge recombination was largely suppressed, which enabled a better ideality factor and a higher efficiency 20.12% for planar PSCs with the increase of donor concentration. The present study will be helpful for understanding the fundamental mechanism within PSCs and achieving high device efficiency.

High performance of mixed halide perovskite solar cells: Role of halogen atom and plasmonic nanoparticles on the ideal current density of cell

To be able to increase the efficiency of perovskite solar cells which is one of the most substantial challenges ahead in photovoltaic industry, the structural and optical properties of perovskite CH3NH3PbI3-xBrx for values x=1-3 have been studied employing density functional theory (DFT). Using the optical constants extracted from DFT calculations, the amount of light reflectance and ideal current density of a simulated single-junction perovskite solar cell have been investigated. The results of DFT calculations indicate that adding halogen bromide to CH3NH3PbI3 compound causes the relocation of energy bands in band structure which its consequence is increasing the bandgap. In addition, the effect of increasing Br in this structure can be seen as a reduction in lattice constant, refractive index, extinction and absorption coefficient. As well, results of the simulation suggest a significant current density enhancement as much as 22% can be achieved by an optimized array of Platinum nanoparticles that is remarkable. This plan is able to be a prelude for accomplishment of solar cells with higher energy conversion efficiency.

Ideal Bandgap Organic-Inorganic Hybrid Perovskite Solar Cells.

Extremely high power conversion efficiencies (PCEs) of ≈20-22% are realized through intensive research and development of 1.5-1.6 eV bandgap perovskite absorbers. However, development of ideal bandgap (1.3-1.4 eV) absorbers is pivotal to further improve PCE of single junction perovskite solar cells (PVSCs) because of a better balance between absorption loss of sub-bandgap photons and thermalization loss of above-bandgap photons as demonstrated by the Shockley-Queisser detailed balanced calculation. Ideal bandgap PVSCs are currently hindered by the poor optoelectronic quality of perovskite absorbers and their PCEs have stagnated at <15%. In this work, through systematic photoluminescence and photovoltaic analysis, a new ideal bandgap (1.35 eV) absorber composition (MAPb0.5 Sn0.5 (I0.8 Br0.2 )3 ) is rationally designed and developed, which possesses lower nonradiative recombination states, band edge disorder, and Urbach energy coupled with a higher absorption coefficient, which yields a reduced Voc,loss (0.45 V) and improved PCE (as high as 17.63%) for the derived PVSCs. This work provides a promising platform for unleashing the complete potential of ideal bandgap PVSCs and prospects for further improvement.

DFT analysis and FDTD simulation of CH3NH3PbI3−xClx mixed halide perovskite solar cells: role of halide mixing and light trapping technique

Since perovskite solar cells have attracted a great deal of attention over the past few years, the enhancement of their optical absorption and current density are among the basic upcoming challenges. For this reason, first, we have studied the structural and optical properties of organic–inorganic hybrid halide perovskite CH3NH3PbI3 and the compounds doped by chlorine halogen CH3NH3PbI3−xClx in the cubic phase by using a density functional theory (DFT). Then, we model a single-junction perovskite solar cell based on a full solution to Maxwell’s equations, using a finite difference time domain (FDTD) technique, which helps us to investigate the light absorption efficiency and optical current density of the cell with CH3NH3PbI3−xClx (x = 0, 1, 2, 3) as the active layer. The results suggest that increasing the amount of chlorine in CH3NH3PbI3−xClx compound leads to an increase in the bandgap energy, as well as a decrease in the lattice constants and optical properties, like the refractive index and extinction coefficient of the structure. Also, the results obtained by the simulation express that by taking advantage of the light trapping techniques of SiO2, a remarkable increase of light absorption will be achieved to the magnitude of 83.13%, which is noticeable.

Low temperature perovskite solar cells with an evaporated TiO2 compact layer for perovskite silicon tandem solar cells

Abstract Silicon-based tandem solar cells can overcome the efficiency limit of single junction silicon solar cells. Perovskite solar cells are particularly promising as a top cell in monolithic tandem devices due to their rapid development towards high efficiencies, a tunable band gap with a sharp optical absorption edge and a simple production process. In monolithic tandem devices, the perovskite solar cell is deposited directly on the silicon cell, requiring low-temperature processes ( 2 ) scaffold - a structure yielding the highest efficiencies for single-junction perovskite solar cells. We show that evaporation of the compact TiO 2 hole blocking layer and ultra-violet (UV) curing for the mesoporous TiO 2 layer allows for good performance, comparable to high-temperature (> 500°C) processes. With both manufacturing routes, we obtain short-circuit current densities (J SC ) of about 20 mA/cm², open-circuit voltages (V OC ) over 1 V, fill factors (FF) between 0.7 and 0.8 and efficiencies (η) of more than 15%. We further show that the evaporated TiO 2 layer is suitable for the application in tandem devices. The series resistance of the layer itself and the contact resistance to an indium doped tin oxide (ITO) interconnection layer between the two sub-cells are low. In addition, the low parasitic absorption for wavelengths above the perovskite band gap allow a higher absorption in the silicon bottom solar cell, which is essential to achieve high tandem efficiencies.

Overcoming the Challenges of Large-Area High-Efficiency Perovskite Solar Cells

For the first time, we report large-area (16 cm2) independently certified efficient single perovskite solar cells (PSCs) by overcoming two challenges associated with large-area perovskite solar cells. The first challenge of realizing a homogeneous and densely packed perovskite film over a large area is overcome by using an antisolvent spraying process. The second challenge of removing the series resistance limitation of transparent conductor is overcome by incorporating a metal grid designed using a semidistributed diode model. A 16 cm2 perovskite solar device at the cell level rather than at the module level is demonstrated using the modified solution process in conjunction with the use of a metal grid. The cell is independently certified to be 12.1% efficient. This work paves the way toward highly efficient and large perovskite cells without single-junction perovskite solar cells and silicon–perovskite tandems.

Hierarchical WO3 nanoflakes architecture with enhanced photoelectrochemical activity

Abstract In the present work, we report on a facile and effective approach to significantly enhance the photoelectrochemical activity of WO3. WO3 nanoflakes with hierarchical architecture prepared with a two-step hydrothermal method exhibits a significant enhancement of photocurrent density by a factor of 1.3 as compared with the pristine counterpart. The improved photoelectrochemical activity could be attributed to the enhanced light-harvesting capability induced by multiple light scattering and better interfacial charge transfer properties by facilitating the exposure of active sites benefited from the hierarchical architecture. An integration of the hierarchical WO3 electrode with a single-junction perovskite solar cell gives a solar energy conversion efficiency of 1.30% without external bias.

Light-Induced Phase Segregation in Halide-Perovskite Absorbers

In the few short years since the inception of single-junction perovskite solar cells, their efficiencies have skyrocketed. Perovskite absorbers have at least as much to offer tandem solar cells as they do for single-junction cells due in large part to their tunable band gaps. However, modifying the perovskite band structure via halide substitution, the method that has been most effective at tuning band gaps, leads to instabilities in the material for some compositions. Here, we discuss the thermodynamic origin and consequences of light-induced phase segregation observed in mixed-halide perovskites. We propose that, as the phase segregation is rooted in halide migration and possibly affected by lattice strain, modifying the perovskite composition and lattice structure, increasing compositional uniformity, and reducing defect concentrations could significantly improve stability.

Comparison of TiO2 and SnO2 Electron Transport Layers in Planar Perovskite Solar Cells

Over the past few years single junction perovskite solar cells have been extensively studied with reported power conversion efficiencies approaching 20% [1-3]. Despite such advances, high efficiency combined with low fabrication cost, parasitic absorptions and long term stability have remained issues. One approach to curtail some of these obstacles has been the investigation of planar architectures where the mesoporous TiO2/Al2O3 is removed from the cell and the electron transport layer (ETL) is reduced to a nanometre scale compact charge blocking layer [4]. Typically this layer has been TiO2 but more recently band gap engineering studies have shown that SnO2 has significant potential in removing TiO2 hysteresis effects whilst maintaining efficiencies [5] In this study we examined planar stacks comprising glass/FTO/ETL/perovskite/spiro MeOTAD hole transport layer/contacts with an aim to further optimize the metal oxide ETL. The metal oxides studied in this work were atomic layer deposition grown SnO2, nominally undoped TiO2 and doped TiO2, all grown at temperatures below 180°C to align with the requirements of silicon-perovskite heterojunction cells [6]. The influence of the ALD growth parameters and composition of the ETL on the subsequent perovskite deposition, as well as the resultant cell performance are highlighted and discussed in terms of efficiency and hysteresis. W.S. Yang et al., Science, 348, 1234-1237 (2015).N.J. Jeon et al., Nature, 517, 476- 480, (2015).S.D. Stranks et al., Science 342, 341-344, (2013)M. Liu et al., Nature, 501, 395- 398, (2013).J.P. Correa Baena, Energy and Environment Science, DOI:10.1039/c5ee02608c, (2015).J.P. Mailoa et al., Applied Physics Letters, 106, 121105 (2015).