Inorganic Hole Transport Layer Research Articles

Numerical Investigation of Electron/Hole Transport Layer for Enhancement of Ecofriendly Tin-Ge Based Perovskite Solar Cell

ABSTRACT The current study examines the influence of different hole transport layers (HTL) and electron transport layers (ETL) on an environmentally friendly CsSn0.5Ge0.5I3 based perovskite solar cell. The numerical analysis of a novel heterojunction structure of FTO/WS2/CsSn0.5Ge0.5I3/Zn3P2/Pt was done using SCAPS software. Initially, a suitable HTL (i.e. Zn3P2) and ETL (WS2) were chosen after analyzing various inorganic HTL and ETL materials. The optimized thickness values of the perovskite film and HTL layer were also measured. Different physical parameters of layers were also measured, such as defect concentration, radiative recombination, energy bandgap of the absorber layer, interface defect concentration, and series and shunt resistances. These analyses revealed that optimizing these parameters improves the electrical rendition of the Tin-Ge-based perovskite solar cell. The photovoltaic cell’s energy conversion efficiency (ECE) value increased to 26.22%, current density (Jsc) to 27.182 mA/cm2, and open-circuit voltage (Voc) to 1.116 V, and fill factor (FF) to 86.40%.

Optimization of tin-based inverted perovskite solar cell with MoS2 interlayer by one-dimensional simulation

Organic–inorganic perovskite solar cells (PSCs) have received extensive attention due to their excellent performances, but most of the absorber layers of such solar cells contain the toxic lead element. Replacing lead with environmentally friendly elements is one of the most essential tasks in the PSCs research field. Tin-based PSCs have emerged owing to their excellent light absorption characteristics. In this work, an Sn-based PSCs inverted structure with molybdenum disulfide (MoS2) as the interfacial layer is proposed, and the performance is studied by the numerical simulation program SCAPS-1D. The influence of the main parameters of the MoS2 layer and absorber layer and the interfacial defect state on the solar cell performance parameters is studied. This study shows that the 20 nm MoS2 layer can improve power conversion efficiency (PCE) by up to 20%. The optimized results from the structure give a PCE of 18.13%, which is comparable to popular solar cells. This work provides a new idea for developing PSCs with a combination of the inorganic hole transport layer and molybdenum disulfide in the future.

Numerical Simulation of Nitrogen-Doped Titanium Dioxide as an Inorganic Hole Transport Layer in Mixed Halide Perovskite Structures Using SCAPS 1-D

Perovskite solar cells (PSCs) stand out as superior third-generation (III-gen) thin-film energy harvesting structures with high efficiency, optical properties and light transmission ability. However, the need to develop cost-effective, stable and sustainable PSCs is allied to the influence of the absorber layer and charge selective transport layers when achieving semi-transparent (ST) structures. Using SCAPS simulation software that can envisage the conceptuality in devising ST PSCs, this work explores and reports the electrical performance of different methylammonium (MA)-based perovskite structures (FTO/TiO2/PCBM/SnO2/MAPbI3/TiO2:N/PTAA/Spiro-OMeTAD/PEDOT: PSS/Ag). The influence of absorber thickness and defect density is analyzed with optimal parameters. This research reports a novel idea that replaces the polymeric hole transport layer (HTL), such as Spiro-OMeTAD, PEDOT: PSS and PTAA with an air-stable inorganic metal oxide, viz., nitrogen-doped titanium dioxide (TiO2:N). The simulation results depict an attainable power conversion efficiency of 9.92%, 10.11% and 11.54% for the proposed structures with the novel HTL that are on par with polymeric HTLs. Furthermore, the maximum allowable absorber thickness was 600 nm with a threshold defect density of 1 × 1015 cm−3. The optimized electrical parameters can be implemented to develop thin-film light transmission perovskite cells with rational power conversion efficiencies.

Recent Advances in Organic and Inorganic Hole and Electron Transport Layers for Organic Solar Cells: Basic Concept and Device Performance

The emergence of nonfullerene small-molecule acceptors (NFSMA) with the advantages of synthetic versatility, high absorption coefficient in wide wavelength range, and high thermal stability has attained the power conversion efficiency (PCE) exceeding 19% for resulted organic solar cells (OSCs) with the optimization of interface engineering and active layer morphology. Interfacial layers including both hole transporting layer (HTL) and electron transporting layer (ETL) are equally important in the OSCs for facilitating electron and hole extraction from the bulk heterojunction (BHJ) photoactive layer by the respective electrodes. In this Review, we summarize the recent progress in the materials used as HTL and ETL in conventional and inverted OSCs on the basis of their effect on the PCE. Finally, the prospects of HTL and ETL materials for NFSMA-OSCs will be provided.

Routes to increase performance for antimony selenide solar cells using inorganic hole transport layers

Simple compound antimony selenide (Sb2Se3) is a promising emergent light absorber for photovoltaic applications benefiting from its outstanding photoelectric properties. Antimony selenide thin film solar cells however, are limited by low open circuit voltage due to carrier recombination at the metallic back contact interface. In this work, solar cell capacitance simulator (SCAPS) is used to interpret the effect of hole transport layers (HTL), i.e., transition metal oxides NiO and MoO x thin films on Sb2Se3 device characteristics. This reveals the critical role of NiO and MoO x in altering the energy band alignment and increasing device performance by the introduction of a high energy barrier to electrons at the rear absorber/metal interface. Close-space sublimation (CSS) and thermal evaporation (TE) techniques are applied to deposit Sb2Se3 layers in both substrate and superstrate thin film solar cells with NiO and MoO x HTLs incorporated into the device structure. The effect of the HTLs on Sb2Se3 crystallinity and solar cell performance is comprehensively studied. In superstrate device configuration, CSS-based Sb2Se3 solar cells with NiO HTL showed average improvements in open circuit voltage, short circuit current density and power conversion efficiency of 12%, 41%, and 42%, respectively, over the standard devices. Similarly, using a NiO HTL in TE-based Sb2Se3 devices improved open circuit voltage, short circuit current density and power conversion efficiency by 39%, 68%, and 92%, respectively.

Suppressing Nickel Oxide/Perovskite Interface Redox Reaction and Defects for Highly Performed and Stable Inverted Perovskite Solar Cells.

The inorganic hole transport layer of nickel oxide (NiOx ) has shown highly efficient, low-cost, and scalable in perovskite photovoltaics. However, redox reactions at the interface between NiOx and perovskites limit their commercialization. In this study, ABABr (4-(2-Aminoethyl) benzoic acid bromide) between the NiOx and different perovskite layers to address the issues has been introduced. How the ABABr interacts with NiOx and perovskites is experimentally and theoretically investigated. These results show that the ABABr molecule chemically reacts with the NiOx via electrostatic attraction on one side, whereas on the other side, it forms a strong hydrogen bond via the NH3 + group with perovskites layers, thus directly diminishing the redox reaction between the NiOx and perovskites layers and passivating the layer surfaces. Additionally, the ABABr interface modification leads to significant improvements in perovskite film morphology, crystallization, and band alignment. The perovskites solar cells (PSCs) based on an ABABr interface modification show power conversion efficiency (PCE) improvement by over 13% and maintain over 90% of its PCE after continuous operation at maximum power point for over 500 h. The work not only contributes to the development of novel interlayers for stable PSCs but also to the understanding of how to prevent interface redox reactions.

Adaption of MAPbI3 perovskite with copper phthalocyanine inorganic hole transport layer via nitrosonium tetrafluoroborate additive to enhance performance and stability of perovskite solar cells

Due to their high resistance to real operational conditions, perovskite-based solar cells (PSCs) with dopant-free inorganic hole transport materials are good candidates for PSC commercialization. It should be noted that these types of PSCs have recorded lower power conversion efficiency (PCE) compared to Spiro-OMeTAD-based PSCs, with a recent PCE record of 25.8%. Here, we introduced nitrosonium tetrafluoroborate (NOBF4) into the perovskite precursor to improve hole carriers' transport between the perovskite layer and copper phthalocyanine (CuPc) layer. Electrochemical impedance spectroscopy (EIS) showed that NOBF4 additive reduces series resistance in PSC devices, which may be due to a band alignment between the valance band of perovskite and CuPc. In addition, due to a partial BF4− substitution with I− ions during the fabrication process, the crystallinity properties of the perovskite layer are tailored, leading to the formation of a film with larger grains. By employing NOBF4 material, in the obtained perovskite layer, a small unreacted lead iodide (PbI2) amount remained. In total, the NOBF4 additive brings a maximum efficiency of 16.77% for the target solar cell group, higher than the 14.42% for control devices. The target PSCs, compared with the control PSCs, showed improved air stability results from the suppressed PbI2 with enlarged perovskite grains.

Roles of Inorganic Oxide Based HTMs towards Highly Efficient and Long-Term Stable PSC-A Review.

In just a few years, the efficiency of perovskite-based solar cells (PSCs) has risen to 25.8%, making them competitive with current commercial technology. Due to the inherent advantage of perovskite thin films that can be fabricated using simple solution techniques at low temperatures, PSCs are regarded as one of the most important low-cost and mass-production prospects. The lack of stability, on the other hand, is one of the major barriers to PSC commercialization. The goal of this review is to highlight the most important aspects of recent improvements in PSCs, such as structural modification and fabrication procedures, which have resulted in increased device stability. The role of different types of hole transport layers (HTL) and the evolution of inorganic HTL including their fabrication techniques have been reviewed in detail in this review. We eloquently emphasized the variables that are critical for the successful commercialization of perovskite devices in the final section. To enhance perovskite solar cell commercialization, we also aimed to obtain insight into the operational stability of PSCs, as well as practical information on how to increase their stability through rational materials and device fabrication.

Spray Pyrolysis Deposition of CuCrO2 Films as Promising Inorganic Hole Transport Layers for Highly Efficient Perovskite Solar Cells

Recently, CuCrO2 films have been successfully introduced as effective hole‐transporting materials in perovskite solar cells (PSCs). However, the long reaction time (≈50–60 h) at the high temperature of hydrothermal synthesis and the complexity of conversion from nanoparticles to uniform films hinder the application of CuCrO2 nanoparticles in PSCs. Herein, a simple, low‐cost, and highly reproducible method for the spray pyrolysis deposition (SPD) of Cu‐deficient CuCrO2 films is reported. The resulting CuCrO2 films exhibit advantages in terms of transparency, roughness, and electrical properties compared to their extensively studied NiO x counterparts. Meanwhile, the deep‐lying valence‐band‐maximum of CuCrO2 films matches very well with that of perovskite materials, minimizing the charge‐extraction barrier. As a result, the excellent electrical properties and energetically favorable energy‐level alignment of the CuCrO2 film allow efficient charge transport from the perovskite layer to the hole transport layer (HTL). Consequently, the optimized CuCrO2‐based device delivers an outstanding power conversion efficiency of 18.86% versus 16.80% for NiO x ‐based devices. This work demonstrates the validity of a CuCrO2 film derived from the SPD method as an HTL for highly efficient PSCs.

85°C/85%-Stable n-i-p Perovskite Photovoltaics with NiOx Hole Transport Layers Promoted By Perovskite Quantum Dots.

Power conversion efficiency (PCE) and long‐term stability are two vital issues for perovskite solar cells (PSCs). However, there is still a lack of suitable hole transport layers (HTLs) to endow PSCs with both high efficiency and stability. Here, NiO x nanoparticles are promoted as an efficient and 85 °C/85%‐stable inorganic HTL for high‐performance n‐i‐p PSCs, with the introduction of perovskite quantum dots (QDs) between perovskite and NiO x as systematic interfacial engineering. The QD intercalation enhances film morphology and assembly regulation of NiO x HTLs . Due to structure–function correlations, hole mobility within NiO x HTL is improved. And the hole extraction from perovskite to NiO x is also facilitated, resulting from reduced trap states and optimized energy level alignments. Hence, the promoted NiO x ‐based n‐i‐p PSCs exhibit high PCE (21.59%) and excellent stability (sustaining 85 °C aging in air without encapsulation). Furthermore, encapsulated solar modules with QDs‐promoted NiO x HTLs show impressive stability during 85 °C/85% aging test for 1000 hours. With high transparency, QDs‐promoted NiO x is also demonstrated to be an advanced HTL for semitransparent PSCs. This work develops promising NiO x inorganic HTL in n‐i‐p PSCs for manufacturing next‐generation photovoltaic devices.

Construction of multilevel network structured carbon nanofiber counter electrode and back interface engineering in all inorganic HTL–free perovskite solar cells

Carbon materials are potential counter electrodes for all−inorganic hole transport layer (HTL)−free perovskite solar cells (PSCs), whereas the defects of the perovskite/carbon back interface are the dominant reason for the low power conversion efficiency (PCE) of this kind of device. To resolve this problem, carbon nanofiber (CNF) was first synthesized using electrospinning technique to construct a carbon counter electrode with porous network architecture by self−supporting nature of CNF. The CsPbBr3 based all−inorganic HTL−free PSCs using the porous CNF counter electrode shows a PCE of 5.01%. To further modify the CsPbBr3/carbon back interface and energy level alignment, mesoporous CNF (m−CNF) and B doped m−CNF (m−BCNF) are synthesized, which can improve the conductivity of the carbon counter electrodes as well as decline the trap state densities and accelerate the carrier extraction and transport properties of the back interface. Accordingly, the all inorganic HTL−free PSCs using m−CNF and m−BCNF counter electrodes generate high PCE of 7.48% and 8.38%, with outstanding long−tern stability. The enhanced PCE improvements can be ascribe to strategies of construction of multilevel network and B doping which can modify the CsPbBr3/carbon back interface, optimize the energy level alignment of the device, and enhance the conductivity of the carbon counter electrode. This research is expected to provide meaningful support for development of new counter electrode materials and back interface engineering for high-performance all inorganic HTL−free PSCs.

Compatibility of Al-doped ZnO electron transport layer with various HTLs and absorbers in perovskite solar cells.

Perovskite solar cells (PSCs) have shown a significant improvement in cell performance in photovoltaics technology. The commonly used light absorbing material of halide-based perovskite in PSCs has produced high efficiency cells with low cost and a simple fabrication process. However, it contains the harmful substance of Pb, which affects the environment, and the cell still suffers from instability in the long run. Therefore, this work presents a theoretical study of the Pb-free absorber layer of CH3NH3SnI3 that is paired for compatibility with various types of hole transport layers (HTLs). Several key parameters of the absorbent layer and HTL have been optimized to produce the highest power conversion efficiency (PCE) using 1D-SCAPS software under AM 1.5 illumination. It was found that the combination of Cu2O and CH3NH3SnI3 used as the HTL and absorbent layer, respectively, has resulted in great PCE as high as 27.72%. These findings prove that the use of inorganic HTLs and Pb-free perovskite layers is promising for use in PSCs.

Improving water-resistance of inverted flexible perovskite solar cells via tailoring the top electron-selective layers

Inverted flexible perovskite solar cells (FPSCs) offer a promising route towards commercialization by using undoped inorganic hole transport layers and thermally-stable electron transport layers (ETLs), which deliver good environmental stability such as water resistance. But the power-conversion-efficiencies (PCEs) of inverted flexible perovskite cells are still far below those of FPSCs in regular configuration so far. One main challenge for achieving high-performance FPSCs lies in optimizing the ETLs and their adjacent buffering layers. Herein, we modify the fullerene derivatives (Phenyl-C61-butyric acid methyl ester, PCBM) ETLs by adding 3-aminopropyl triethoxysilane (APTS) molecules into the PCBM solutions. The addition of APTS results in smoother and denser PCBM layers via a physically steric-hindrance effect mechanism, which could benefit the electron collection between the PCBM layer and the perovskite layer. More importantly, APTS can offer nucleating sites, such as amine groups or hydroxy groups by partially hydrolyzing, to grow conformal tin oxide (SnO x ) layers by atomic layer deposition (ALD), which acts as robust buffer layers to replace traditional bathocuproine (BCP) layer. Finally, high-performance inverted FPSCs based on the optimized PCBM/SnO x electron-selective layers are fabricated, delivering a best PCE of 18.62%. The unencapsulated FPSC showed a slow decay and remained above 90% of its initial PCE after being stored for more than 600 h in a damp environment with a humidity of more than 85% R.H. The strategy is demonstrated to be applicable in the future large-scale production of stable FPSCs. • A flatter PCBM layer can reduce contact resistance and improve electron collection in inverted perovskite solar cells. • Modifying the PCBM layer with silane agents is helpful for the subsequent ALD growth of the inorganic buffer layer. • An optimized PCBM/SnO x electron selective layer endows flexible perovskite solar cells with outstanding water resistance.

Low-Cost Inorganic Strontium Ferrite a Novel Hole Transporting Material for Efficient Perovskite Solar Cells.

Perovskite solar cells attract significant interest due to their high-power conversion efficiencies. The replacement of charge-transporting layers using inorganic materials is an effective approach for improving stability and performance, as these materials are low-cost, highly durable, and environmentally friendly. This work focuses on the inorganic hole and electron transport layers (HTL and ETL), strontium ferrite (SrFe2O4), and zinc oxide (ZnO), respectively, to enhance the efficiency of perovskite solar cells. Favorable band alignment and high charge-collection capability make these materials promising. Experimental and computational studies revealed that the power conversion efficiency of the fabricated device is 7.80% and 8.83%, respectively. Investigating electronic properties and interface charge transfer through density functional theory calculations further corroborated that SrFe2O4 is a good HTL candidate. Our numerical device modeling reveals the importance of optimizing the thickness (100 nm and 300 nm) of the HTL and perovskite layers and defect density (1016 cm−3) of the absorber to achieve better solar cell performance.

Oxidized Nickel to Prepare an Inorganic Hole Transport Layer for High-Efficiency and Stability of CH3NH3PbI3 Perovskite Solar Cells

In this study, we report a perovskite solar cell (PSC) can be benefited from the high quality of inorganic nickel oxide (NiOx) as a hole transport layer (HTL) film fabricated from the physical vapor deposition (PVD) process. The power conversion efficiency (PCE) of PSC is found to depend on the thickness of NiOx HTL. The NiOx thickness is optimized via quantitative investigation of the structure, optical and electrical properties. With an active area of 11.25 cm2, a PSC module (25 cm2) with a PCE of 15.1% is demonstrated, while statistically averaged PCE = 18.30% with an open voltage (Voc) 1.05 V, short-circuit current density (Jsc) 23.89 mA/cm2, and fill factor (FF) 72.87% can be achieved from 36 devices with smaller active areas of 0.16 cm2. After the stability test at 40% relative humidity (RH) and 25 °C for 1200 h, the highest performance NiOx-based PSC is shown to be about 1.2–1.8 times superior to PEDOT:PSS organic HTL based PSC at the same environment.

Efficient and Stable Perovskite Solar Cells Based on Inorganic Hole Transport Materials.

Although power conversion efficiencies of organic-inorganic lead halide perovskite solar cells (PSCs) are approaching those of single-crystal silicon solar cells, the working device stability due to internal and external factors, such as light, temperature, and moisture, is still a key issue to address. The current world-record efficiency of PSCs is based on organic hole transport materials, which are usually susceptible to degradation from heat and diffusion of dopants. A simple solution would be to replace the generally used organic hole transport layers (HTLs) with a more stable inorganic material. This review article summarizes recent contributions of inorganic hole transport materials to PSC development, focusing on aspects of device performance and long-term stability. Future research directions of inorganic HTLs in the progress of PSC research and challenges still remaining will also be discussed.

Performance Comparison of Different Hole Transport Layer Configurations in a Perovskite-based Solar Cell using SCAPS-1D Simulation

Due to the solar cell industry, environmentally friendly and low-cost electricity generation processes, the use of non-renewable energy sources, especially fossil fuels, is developing day by day. Among the different solar cells under use, perovskite solar cells have recently experienced rapid growth in research due to their high performance and low production costs at the same time. Perovskite solar cells typically consist of some main layers such as absorbent, carrier layers and electrodes. The hole transport layer (HTL) is very important in the perovskite solar cell structure due to its important role in cell performance. The light absorbed by the perovskite layer leads to the formation of electrons and holes. These load carriers are then transported to the electrodes by the electron and hole transport layers. There are several types of HTL, such as small molecules in the cell structure, polymeric and inorganic HTLs. In addition, these different options can be in various configurations such as tandem, composite and single structures. In this study, three common HTL types, Spiro-OMeTAD, P3HT and Cu2O, were studied and their effects on cell performance in different composite, tandem and single forms were investigated and their results were compared. These comparisons were made in the simulation environment in SCAPS-1D software. The final results showed approximately the best 27% efficiency of the use of tandem structure in the HTL configuration with Spiro-OMeTAD and P3HT in the special perovskite solar cell created in this study.

Device modeling of non-fullerene organic solar cell by incorporating CuSCN as a hole transport layer using SCAPS

Heterojunction organic solar cells with a non-fullerene acceptor (NFA-BHJ-OSC) with inorganic hole transport layer (HTL) have drawn a lot of cognizance due to their greater efficiency compared with traditional Fullerene acceptor solar cells. The most often adopted HTL, PEDOT:PSS, degrades the device, due to the hygroscopic and acidic nature of PSS. Therefore, an alternate hole transport material is necessary to optimize the output of OSCs. A simulation on the performance of NFA-BHJ-OSC with an active layer of PBDB-T/ITIC incorporated with Copper (I) thiocyanate (CuSCN) as an HTL, is performed in the present paper using the software SCAPS 1-D. CuSCN is a p-type semiconductor having wider energy band gap in comparison to other inorganic hole transport materials. In the present simulation based work, NFA-OSC having CuSCN as the hole transport layer shows the optimized PCE of 20.36%, Fill Factor (FF) of 66.88%, JSC of 33.09 mA/cm2 and VOC of 1.0341 V by varying physical parameters such as active layer thickness, temperature, and properties of HTL and ETL. These values are promising to develop NFA-OSCs incorporating CuSCN as a HTL in the near prospect.

Steering Interface Dipoles for Bright and Efficient All-Inorganic Quantum Dot Based Light-Emitting Diodes.

The state-of-the-art quantum dot (QD) based light-emitting diodes (QD-LEDs) reach near-unity internal quantum efficiency thanks to organic materials used for efficient hole transportation within the devices. However, toward high-current-density LEDs, such as augmented reality, virtual reality, and head-up display, thermal vulnerability of organic components often results in device instability or breakdown. The adoption of a thermally robust inorganic hole transport layer (HTL), such as NiO, becomes a promising alternative, but the large energy offset between the NiO HTL and the QD emissive layer impedes the efficient operation of QD-LEDs. Here, we demonstrate bright and stable all-inorganic QD-LEDs by steering the orientation of molecular dipoles at the surfaces of both the NiO HTL and QDs. We show that the molecular dipoles not only induce the vacuum level shift that helps alleviate the energy offset between the NiO HTL and QDs but also passivate the surface trap states of the NiO HTL that act as nonradiative recombination centers. With the facilitated hole injection into QDs and suppressed electron leakage toward trap sites in the NiO HTL, we achieve all-inorganic QD-LEDs with high external quantum efficiency (6.5% at peak) and brightness (peak luminance exceeding 77 000 cd/m2) along with prolonged operational stability. The approaches and results in the present study provide the design principles for high-performance all-inorganic QD-LEDs suited for next-generation light sources.

Ultra-stable all-inorganic silver bismuth sulfide colloidal nanocrystal photovoltaics using pin type architecture

Silver bismuth sulfide (AgBiS2) colloidal nanocrystals (NCs) have emerged as an environmentally friendly light absorber for next-generation photovoltaics. Classical AgBiS2 NC photovoltaics with nip-architecture have been mandated to use a combination of polymer and molybdenum oxide as a hole transport layer (HTL), which are vulnerable to oxygen, heat and water. In this work, we develop all-inorganic AgBiS2 NC photovoltaics with pin-architecture, serving a nickel oxide (NiO) as HTL. We also employ a cascade-energy-level alignment by introducing 3-mercaptopropionic acid-treated AgBiS2 NC layer, enabling enhanced hole collection with minimized interfacial recombination. As a result, the pin type AgBiS2 NC photovoltaics demonstrate a power conversion efficiency of 5.59% as well as excellent stability even under extreme conditions such as heat and water exposures, attributed to superior chemical robustness of the inorganic HTL. This work is the first report on AgBiS2 NC device with all-inorganic components and achieves the highest device efficiency in pin type AgBiS2 NC photovoltaics.