Structure Perovskite Solar Cells Research Articles

Bottom-contact passivation for high-performance perovskite solar cells using TaCl5-doped SnO2 as electron-transporting layer

Abstract Organic-inorganic hybrid perovskite solar cells (PSCs) possess the promising potential to substitute photovoltaic technologies in the traditional model. The modified SnO2 as an electron-transporting layer (ETL) has been studied extensively because of its excellent properties. Herein, we implemented the TaCl5 doped SnO2 ETL in the n-i-p structure perovskite solar cells. The doped SnO2 solution was demonstrated the characterization of neutral power of value and hydrophobicity. The conduction band of changed ETLs shifted downward by 0.26 eV resulting in the efficient electron transfer. Furthermore, the doped SnO2 films affect the perovskite crystallite size with passivated traps and reduced nonradiative recombination loss. After employing TaCl5-doped SnO2 ETL, the open-circuit voltage enhances from 0.97 to 1.08 V and a united power conversion efficiency increases from 16.38% to 18.23% achieved when adopted 1.0 wt% doped TaCl5–SnO2 TEL. The developed doping method provides an effective method to passivate SnO2 for fabricating high-performance perovskite solar cells.

Stable and Highly Flexible Perovskite Solar Cells with Power Conversion Efficiency Approaching 20% by Elastic Grain Boundary Encapsulation

Here, we show that flexible perovskite solar cells (PSCs) with high operational stability and power conversion efficiency (PCE) approaching 20% were achieved by elastic grain boundary (GB) encapsul...

Numerical development of eco-friendly Cs2TiBr6 based perovskite solar cell with all-inorganic charge transport materials via SCAPS-1D

The commercial implementation of lead-based perovskite solar cell faces a major impediment due to the toxicity and stability issue. In such circumstances, Ti-based all-inorganic perovskite solar cells can be imperative in the commercialization of high-performance perovskite solar cells (PSC). Herein we propose a theoretical study of a lead-free, eco-friendly, and stable Cs2TiBr6 based all-inorganic n-i-p structured perovskite solar cell with the application of all-inorganic charge transport materials for higher stability. Analyzing factors like charge transport materials and their thickness, absorber thickness, absorber defect density, and interface defect density, we have proposed a high-performance PSC with efficiency as much as 11.49 % at ambient temperature. The elicited results suggest that Cs2TiBr6 can play a momentous role as an absorbing perovskite towards the highly efficient lead-free all-inorganic perovskite solar cell technology.

Highly stable perovskite solar cells based on perovskite/NiO-graphene composites and NiO interface with 25.9 mA/cm2 photocurrent density and 20.8% efficiency

Perovskite solar cells (PSCs) demonstrated a record-high power conversion efficiency, but they have instability issues attributed to the degradation of materials and device performance. To overcome the instability problem and performance degradation, various methods have been proposed, but still need a comprehensive solution. Here, we propose an innovative way of insuring device performance and long-term stability by utilizing functional composites of perovskite, nickle oxide and graphene into device structures. We fabricated the PSCs based on MAPbI 3−x Cl x /NiO-graphene photoactive composite and NiO interface layer. Compared to the pristine perovskite cells, the champion device based on the photoactive composites with NiO interface showed remarkably high photocurrent density of 25.9 mA/cm 2 (i.e., 95.2% of theoretical maximum) and power conversion efficiency of 20.8% without J-V hysteresis. More impressively, unencapsulated cells showed significant improvement of thermal- and photo- and long-term air-stability with retaining 97–100% of the initial values of performance parameters over 310 days under ambient conditions. Schematic illustration of a perovskite solar cell structure based on MAPbI 3−x Cl x /NiO-rGO composite photoactive layer and NiO interface formed on the SrTiO 3 /Al 2 O 3 -graphene electron transfer layer, exhibiting the mechanism of charge carrier separation and conduction through graphene and connected NiO nanoparticles and blocking moisture and oxygen infiltration. • Highly stable and efficient composites-based perovskite solar cells. • Perovskite/NiO-graphene photoactive composite and NiO interface layer. • Remarkably high photocurrent density and power conversion efficiency without J-V hysteresis. • Significant improvement of thermal- and photo- and air-stability with retaining 97–100% of device performance over 310 days.

Can the efficiencies of simplified perovskite solar cells go higher?

Simplified structures of perovskite solar cells can reduce the fabrication and materials cost while simultaneously achieving high efficiencies, which are highly attractive for practical industrial production.

Intermittent sulfurization—a method promoting Macro-Porous Cu-Poor Zn-Rich—kesterite CZTS as HTM for inverted perovskite solar cell application

Porous semiconductors have emerged as a lucrative apparatus for energy-harvesting applications with more exceptional ability as compared to their bulk counterpart. Exposure of a new porous formation strategy for the abundant semiconductor CZTS could initiate an extensive exploration for solar cell applications. Available porous formation strategies for the CZTS have neglected a significant factor of its compositional balance, which needs to be assisted carefully. In this work, intermittent sulfurization technique is used to promote macro-porous CZTS towards perovskite solar cell applications. This technique not only promotes the macro-porosity of CZTS but also successfully controls its compositional balance to fulfill the favorable Cu-poor Zn-rich condition. Every tuned step of this technique causes a different morphology and composition, which has been investigated by FESEM and EDX mapping. Meanwhile, characterization of phase, crystallinity, and optical bandgap have also been investigated by XRD, Raman spectroscopy, and UV–Vis spectroscopy, respectively, for the resulted in macro-porous Kesterite CZTS. Inverted (p-i-n)-structured perovskite solar cell with p-type macro-porous CZTS as hole transporter material delivered 3.33% power conversion efficiency. Synthesis of perovskite material and electron transporting material along with the fabrication of (p-i-n)-structured perovskite solar cells have also been detailed here.

Synergetic Effect of Plasmonic Gold Nanorods and MgO for Perovskite Solar Cells.

We report new structured perovskite solar cells (PSCs) using solution-processed TiO2/Au nanorods/MgO composite electron transport layers (ETLs). The proposed method is facile, convenient, and effective. Briefly, Au nanorods (NRs) were prepared and introduced into mesoporous TiO2 ETLs. Then, thin MgO overlayers were grown on the Au NRs modified ETLs by wet spinning and pyrolysis of the magnesium salt. By simultaneous use of Au NRs and MgO, the power conversion efficiency of the PSC device increases from 14.7% to 17.4%, displaying over 18.3% enhancement, compared with the reference device without modification. Due to longitudinal plasmon resonances (LPRs) of gold nanorods, the embedded Au NRs exhibit the ability to significantly enhance the near-field and far-field (plasmonic scattering), increase the optical path length of incident photons in the device, and as a consequence, notably improve external quantum efficiency (EQE) at wavelengths above 600 nm and power conversion efficiency (PCE) of PSC solar cells. Meanwhile, the thin MgO overlayer also contributes to enhanced performance by reducing charge recombination in the solar cell. Theoretical calculations were carried out to elucidate the PV performance enhancement mechanisms.

Optimizing the working mechanism of the CsPbBr3-based inorganic perovskite solar cells for enhanced efficiency

Recently, inorganic perovskite solar cells (PSCs) based on CsPbBr3 have triggered incredible interest due to the demonstrated excellent stability against thermal and high humidity environmental conditions. However, the power conversion efficiency (PCE) of the CsPbBr3-based PSCs is still lower than that of the organic-inorganic hybrid one, because of the large band gap and serious charge recombination at the interface or inside the device. Here, the working mechanism of the devices with normal n-i-p planar structure is modeled and investigated using SCAPS 1D simulation software. The simulation results state that the proper band structure of PSCs is crucial to carrier separation and transport. The high interface recombination, originated from the large band offsets of the electron transport material (ETM)/absorber and absorber/hole transport material (HTM) respectively, can be effectively diminished with the continuous gradient junction design of the absorber, and a PCE of 11.58% is obtained with a high open-circuit voltage (VOC) of 1.68 V. Moreover, by building a heterojunction bilayer absorption scenario of CsPbIBr2/CsPbBr3 and employing ZnOS and Cu2ZnSnS4 films as the ETM and HTM respectively, the PCE of PSCs is further increased to 15.89%, caused mainly by the enhancement in short-current density (JSC). Moreover, reducing the interface defect density is also very important to improve the performance of PSCs. These results will provide theoretical guidance for improving the performance of the CsPbBr3-based PSCs.

Low-temperature processed, stable n-i-p perovskite solar cells with indene-C60-bisadduct as electron transport material

Organo-metallic halide perovskites (OMHP) have proven to be promising light absorbers with superb optoelectronic properties for developing the next generation of low-cost solar cells. Over the past years, the extensive research efforts on perovskite solar cells (PSCs) have led to an impressive improvement in the photovoltaic performance on many fronts and have their main field of applications in low-temperature and low power consumption photo-electronic devices, However, a wide range of highly performing PSCs structures involves the use of metal oxide electron transport materials (ETMs) such as TiO2 which requires high processing temperature that could result in a higher manufacturing energy input and cost. This also could hinder the development of low-cost and low-temperature scalable processes for device fabrication on rigid or flexible substrates. Here, we develop a low-temperature procedure (below 100 °C) that make use of Indene-C60 Bisadduct (ICBA) as an alternative ETM in the planar n-i-p-structured PSCs. After modifying the ICBA layer, we not only improved the optimum performance and stability of the device, but also study its influence on the device operation using impedance spectroscopy, and finally achieved a stabilized power conversion efficiency of 13.5%. Thereby, this study will establish low-temperature ETM as an outstanding candidate for future high stability PSCs production due to its high performance, low process temperature and easy fabrication.

Surface Modification of NiO Nanoparticles for Highly Stable Perovskite Solar Cells Based on All-Inorganic Charge Transfer Layers

In the conventional n-i-p structure of perovskite solar cell (PSC), spiro-OMeTAD is used as the hole transport layer. However, some additives in spiro-OMeTAD, such as LiTFSI and TBP, can bring risks for perovskite degradation. Nickel oxide (NiO), a wide-band gap (3.6–4.0 eV) p-type semiconductor material with excellent electrical and optical properties, is widely applied in the PSCs and other fields. Given the suitable valence and conduction bands, NiO can effectively block electrons and transport holes, which are generated in the perovskite film after illumination. However, depositing a compact and thin NiO layer on the perovskite film is difficult because of the heat and solvent sensitivity of organic–inorganic hybrid perovskite. Here, we propose a facile method to prepare well-dissolved NiO nanoparticles in chlorobenzene, and the NiO film on perovskite is further modified by oxygen plasma or hexanethiol treatment to enhance the hole conductivity. Finally, we obtain a n-i-p structured PSC on the basis of all-inorganic charge transport layer with an efficiency of 4.21% using the prepared NiO film, and the value is further improved to 6.10% after oxygen plasma post-treatment. Moreover, the working stability is enhanced remarkably as the spiro-OMeTAD is replaced by NiO film, which is important for the application of PSCs.

A novel leaves and needles like TiO2 (LNT) electron transfer layer (ETL) as an alternative to meso-porous TiO2 electron transfer layer (ETL) in perovskite solar cell

Abstract Two perovskite solar cells one with leaves and needles like TiO2 (LNT) and other with meso-porous TiO2 as electron transfer layer (ETL) were fabricated. The perovskite solar cell structure FTO/Compact-TiO2/LNT/CH3NH3PbBr3/Spiro-OMeTAD/Ag with leaves and needles like TiO2 electron collector, exhibit high efficiency up to 9% being supported by high open-circuit voltage and fill factor up to 0.8 V and 0.89, respectively. The second perovskite solar cell structure FTO/Compact-TiO2/Meso-porous TiO2/CH3NH3PbBr3/Spiro-OMeTAD/Ag with meso-porous TiO2 electron collector, efficiency is 6.2% with open-circuit voltage and fill factor up to 0.77 V and 0.71 respectively. As compared to meso-porous TiO2 electron collector layer, leaves and needles like TiO2 has better electron band alignment with compact TiO2 as hole blocking layer and hence, results in higher efficiency.

Mixed Fullerene Electron Transport Layers with Fluorocarbon Chains Assembling on the Surface: A Moisture-Resistant Coverage for Perovskite Solar Cells.

In p-i-n structure perovskite solar cells (PSCs), the most prevalent electron transport layer (ETL), [6, 6]-phenyl-C61-butyric acid methyl ester (PC61BM), acts as both electron extractor and protective coverage to the underlayer perovskite. Notably, multifunctional mixed fullerene ETLs show great potential in further improving both the power conversion efficiency (PCE) and stability of PSCs compared to the single PC61BM ETL. In this work, we reported the mixed fullerene ETLs comprising of PC61BM and its two analogs with different length of fluorocarbon chains, [6, 6]-phenyl-C61-buryric acid 1H,1H-trifluoro-1-ethyl ester (abbreviated, CF3-PC61BM) and [6, 6]-phenyl-C61-buryric acid 1H, 1H-tridecafluoro-1-heptyl ester (abbreviated, C6F13-PC61BM). We obtained excellent PCEs of 18.37% and 17.71% for 1 wt % CF3-PC61BM- and C6F13-PC61BM-based PSCs (1 wt % addition of PC61BM) with CH3NH3PbI3 (MAPbI3) perovskites, respectively. Moreover, champion PCEs of ∼19% were obtained based on the CsFAMAPbIBr perovskites. Subsequent experiments demonstrated that the fluorocarbon chains of CF3-PC61BM and C6F13-PC61BM assembled at the surfaces of ETLs with the formation of thin-layer moisture-resistant protective coverage above perovskite. Results show that it significantly retarded water penetrating down to perovskite layers and led to optimal humidity stability under ambient atmosphere.

Numerical modeling and simulation for augmenting the photovoltaic response of HTL free perovskite solar cells

Organo-metal halide perovskites have drawn a lot of appeal from the research community in recent years because of its application as an absorber in thin-film solar cells. However, the fabrication of multi-layered defect-free planar perovskite solar cell (PSC) structures is a very challenging task. This is because the interface between charge transport layer/perovskite materials promotes hysteresis and recombination leading to poor long term stability. Along with the mechanism of charge transport, the dependence of performance on the material parameters in hole transport layer (HTL)-free PSCs is unclear. Removal of the HTL layer from the standard configuration in PSC degrades the device performance. In this paper, a novel HTL-free PSC employing glass/FTO/TiO2/CH3NH3Pb(I1-xBrx)3/Au contact structure has been investigated using a one-dimensional modeling program AMPS-1D. It was demonstrated that to achieve better photovoltaic performance, the thickness of the absorber should be increased; the acceptor doping concentration should be of the order of ∼ 1017 and the bandgap should be modified to 1.7 eV. Under moderate simulation conditions, if the above factors are satisfied, efficiencies over 17% can be attained.

Acetamidinium Cation to Confer Ion Immobilization and Structure Stabilization of Organometal Halide Perovskite Toward Long Life and High‐Efficiency p‐i‐n Planar Solar Cell via Air‐Processable Method

Ion migration in organometal halide perovskite solar cell (OHPSC) and crystal structure evolution of organometal halide perovskites (OHPVSKs) in air are considered as one of the critical factors for unstable performance and of the urgent issues for the reliability of OHPSCs. Herein, a novel cation of acetamidinium (Aa+) with stronger coordinated bond with I− than methylammonium is induced into OHPVSK to stabilize its crystal structure. By incorporating Aa+ ions into OHPVSKs, the power conversion efficiency (PCE) of OHPSC without an encapsulation can maintain higher than 75% of its initial PCE after a 200 h humidity (60–80% relative humidity (RH) in air) or a 24 h thermal stress test (85 °C in dry N2). The Aa–MAPbI3 device exhibits an outstanding efficiency of 20.68%, and over 80% of initial PCE is maintained after a 1300 h damp heat as encapsulated. This novel cation can be easily incorporated into OHPVSK via a hot casting process in air with a high environmental tolerance as compared with that from the conventional coating process, which suffers from sophisticated crystallization steps and a strict processing atmosphere. It extends processing windows for OHPVSK fabrication and provides a promising path toward mass production and further commercialization.

Numerical analysis of high-efficiency lead-free perovskite solar cell with NiO as hole transport material and PCBM as electron transport material

In this work a lead free perovskite solar cell structure is proposed with NiO as the hole transport material (HTM), CH3NH3SnI3 as the perovskite absorber material and PCBM (phenyl C61 butyric acid methyl ester) as the electron transport material (ETM). Numerical analysis of the designed solar cell is performed using Solar Cell Capacitance Simulator (SCAPS-1D) program. The power conversion efficiency (PCE) of the optimized device stack is found to be above 29% with Voc = 0.98 V, Jsc = 34.86 mA/cm2, FF = 85.64%. The lead free perovskite solar cell with different HTM and ETM may be investigated for high PCE.

Hysteresis-less and stable perovskite solar cells with a self-assembled monolayer

Organic–inorganic halide perovskites are promising for use in solar cells because of their efficient solar power conversion. Current–voltage hysteresis and degradation under illumination are still issues that need to be solved for their future commercialization. However, why hysteresis and degradation occur in typical perovskite solar cell structures, with an electron transport layer of metal oxide such as SnO2, has not been well understood. Here we show that one reason for the hysteresis and degradation is because of the localization of positive ions caused by hydroxyl groups existing at the SnO2 surface. We deactivate these hydroxyl groups by treating the SnO2 surface with a self-assembled monolayer. With this surface treatment method, we demonstrate hysteresis-less and highly stable perovskite solar cells, with no degradation after 1000 h of continuous illumination.

Interfacial Modification of Mesoporous TiO2 Films with PbI2-Ethanolamine-Dimethyl Sulfoxide Solution for CsPbIBr2 Perovskite Solar Cells.

As one of the most frequently-used electron-transporting materials, the mesoporous titanium dioxide (m-TiO2) film used in mesoporous structured perovskite solar cells (PSCs) can be employed for the scaffold of the perovskite film and as a pathway for electron transport, and the contact area between the perovskite and m-TiO2 directly determines the comprehensive performance of the PSCs. Because of the substandard interface combining quality between the all-inorganic perovskite CsPbIBr2 and m-TiO2, the development of the mesoporous structured CsPbIBr2 PSCs synthesized by the one-step method is severely limited. Here, we used a solution containing PbI2, monoethanolamine (EA) and dimethyl sulfoxide (DMSO) (PED) as the interfacial modifier to enhance the contact area and modify the m-TiO2/CsPbIBr2 contact characteristics. Comparatively, the performance of the solar device based on the PED-modified m-TiO2 layer has improved considerably, and its power conversion efficiency is up to 6.39%.

Validated Analysis of Component Distribution Inside Perovskite Solar Cells and Its Utility in Unveiling Factors of Device Performance and Degradation.

Time-of-flight secondary-ion mass spectrometry (ToF-SIMS) has been used for gaining insights into perovskite solar cells (PSCs). However, the importance of selecting ion beam parameters to eliminate artifacts in the resulting depth profile is often overlooked. In this work, significant artifacts were identified with commonly applied sputter sources, i.e., an O2+ beam and an Ar-gas cluster ion beam (Ar-GCIB), which could lead to misinterpretation of the PSC structure. On the other hand, polyatomic C60+ and Ar+ ion beams were found to be able to produce depth profiles that properly reflect the distribution of the components. On the basis of this validated method, differences in component distribution, depending on the fabrication processes, were identified and discussed. The solvent-engineering process yielded a homogeneous film with higher device performance, but sequential deposition led to a perovskite layer sandwiched by methylammonium-deficient layers that impeded the performance. For device degradation, it was found that most components remained intact at their original position except for iodide. This result unambiguously indicated that iodide diffusion was one of the key factors governing the device lifetime. With the validated parameters provided, ToF-SIMS was demonstrated as a powerful tool to unveil the structure variation amid device performance and during degradation, which are crucial for the future development of PSCs.

Pressure-Assisted Fabrication of Perovskite Solar Cells

This paper presents the results of a combined experimental and analytical/computational study of the effects of pressure on photoconversion efficiencies of perovskite solar cells (PSCs). First, an analytical model is used to predict the effects of pressure on interfacial contact in the multilayered structures of PSCs. The PSCs are then fabricated before applying a range of pressures to the devices to improve their interfacial surface contacts. The results show that the photoconversion efficiencies of PSCs increase by ~40%, for applied pressures between 0 and ~7 MPa. However, the photoconversion efficiencies decrease with increasing pressure beyond ~7 MPa. The implications of the results are discussed for the fabrication of efficient PSCs.

Fabrication and TCAD validation of ambient air-processed ZnO NRs/CH3NH3PbI3/spiro-OMeTAD solar cells

This paper reports the fabrication, characterization and simulation of hybrid perovskite solar cells (PSCs) in ambient condition. The proposed PSC structures use a CH 3 NH 3 PbI 3 hybrid perovskite based active layer sandwiched between a ZnO nanorods (NRs) electron transport layer (ETL) and a spiro-OMeTAD (undoped and doped) hole transport layer (HTL). The ZnO NRs are grown using low-cost solvothermal process at relatively low temperature. The performance of fabricated PSCs are analyzed for both the undoped and doped (with TBP and LiTFSI) spiro-OMeTAD based HTLs. All the solar parameters namely, short circuit current density ( J SC ), open circuit voltage ( V OC ), fill factor ( FF ), power conversion efficiency ( PCE ) and external quantum efficiency ( EQE ) are calculated from experimentally measured current density versus voltage ( J-V ) and wavelength transient characteristics in ambient condition. The maximum PCE of 10.18% is obtained for the doped HTL whereas 9.51% for undoped HTL. The improved performance due to HTL doping is attributed to the enhanced charge transportation of the HTL. The experimental results obtained from the fabricated PSCs are also compared with the SetFos™ TCAD simulation data using drift-diffusion model. The simulated results are observed to be well matched to the experimental data. • PSCs with 10.18% PCE fabricated under ambient-air atmosphere. • PSCs for undoped and doped HTL validated using SetFos™ TCAD simulation. • ZnO NRs grown by solvothermal process upon ZnO QDs sheet layer coated on FTO.