Inorganic Hole Transport Layer Research Articles

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.

Graphdiyne oxide modified nano CuO as inorganic hole transport layer for efficient and stable organic solar cells

With the rapid development of organic solar cells (OSCs), the stability of devices has gradually attracted researcher’s attention. The characteristics of hole transport layer (HTL) have a crucial influence on the stability and performance of OSCs. Inorganic semiconductor CuO nanomaterials with high transmittance, good stability, low cost and rich raw materials were chosen as hole transport materials for the fabrication of high-efficiency OSCs. In this work, graphdiyne oxide (GDYO) as an interface modifier was introduced into CuO nanofilm to improve its conductivity and reduce the contact resistance between HTL and the active layer. As a result, the PM6:Y6 based OSCs with CuO (GDYO) as HTL exhibit a high power conversion efficiency (PCE) of 16.61% with simultaneous improvements on short-circuit current density and fill factor compared with the unmodified devices. The performance improvement of the device is mainly attributed to the increased hole mobility and reduced charge recombination by adding an appropriate amount of GDYO. To prove its universality, a PCE of 16.74% (PM6:Y6-BO-4Cl) and a PCE of 9.19% (PTB7-Th:PC71BM) of OSCs were obtained based on CuO (GDYO) as HTL. CuO (GDYO) based OSCs have obtained the highest efficiency among inorganic HTLs when using same active layer materials, and are also better than the reported poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) based devices. In addition, the stability of all CuO (GDYO) based OSCs can still be maintained above 65% after 30 h in air without any encapsulation. The results suggest that GDYO modified CuO as HTL has great potential in fabrication of high efficient and stable OSCs.

Simulated development and optimized performance of narrow-bandgap CsSnI3-based all-inorganic perovskite solar cells

As perovskite solar cell (PSC) technology is about to be commercialized, the use of toxic and organic material is still a problem. At the same time, CsSnI3 has received widespread attention because of its narrow bandgap and non-toxicity. In this study, we use the wxAMPS tool to investigate the limitations of Sn-based all-inorganic PSCs, using CsSnI3 perovskite as the absorption layer and Au as the back electrode to create non-toxic all-inorganic PSCs. CsSnI3 is a narrow-band material; the absorption range can be extended to the near-infrared spectral region, and it has a very high hole mobility. Therefore, this article first compares several potential inorganic electron and hole transport layers (ETLs and HTLs), and the results show that C60 ETL and MoOx HTL are the most suitable materials. Moreover, the device performance is further improved by optimizing the absorber thickness as well as the doping density. Under optimized conditions, a conversion efficiency of 19.25% is obtained for the FTO/C60/CsSnI3/MoOx/Au PSCs, indicating that there is much room for further performance enhancement. The photovoltaic performance parameters achieve their optimum value at an absorber thickness is better among the range of 100–1300 nm and doping density of 1019 cm−3. This shows that the proposed non-toxic all-inorganic PSCs have broad prospects in future photovoltaic and optoelectronics applications, and provide theoretical guidance for the manufacture of a non-toxic and inorganic PSCs.

Computational analysis of chalcogenides as an inorganic hole transport layer in perovskite solar cells

Fill factor (FF) deficit and stability is a primary concern and challenge with the perovskite solar cell. The band alignment and resistance at the junction interface further decreases the fill factor and thus limits the performance of the device. Moreover, degradation of the intrinsic properties of the upcoming perovskite material such as methylammonium lead halide on exposure to ambience or moisture creates instability and decreases the shelf life of the device. To overcome all these challenges, we have engineered the device structure and introduces an earth-abundant material in the primitive perovskite structure by introducing an inorganic hole transport layer (HTL). It was observed from the calculation that the FF is sensitive to the band offset values. Moreover, the band alignment/band offset role and effect at the Perovskite/HTL junction were investigated. It is evident from the calculation that the inorganic material replacing Spiro-MeOTAD can enhance the stability of the device by providing insulation from ambient. The efficiency of SnS and spiro-MeOTAD were found to be comparable in the present work and thus the shelf life and moisture sensitivity challenge of the perovskite solar cell is addressed. Moreover, this work paves the way for earth-abundant p-type chalcogenides tin selenide (SnS) as a HTL layer in the perovskite solar cell.

Alloyed (Cu2SnS3)x(ZnS)1−x quantum dots as a hole-transporting layer for efficient and stable perovskite solar cells

In the present study, alloyed (Cu2SnS3)x(ZnS)1−x quantum dots (QDs) were prepared by combining Cu2SnS3 and ZnS. The alloyed (Cu2SnS3)x(ZnS)1−x was applied to perovskite solar cells (PSCs) as an inorganic hole transport layer. The power conversion efficiency (PCE) of the solar cells based on (Cu2SnS3)x(ZnS)1−x was optimized by tuning the content of ZnS. A high PCE of 17.02% was obtained for the solar cells based on the optimized (Cu2SnS3)0.7(ZnS)0.3 quantum dots, while that of the solar cells based on Cu2SnS3 was 15.96%. The experimental data demonstrate that the enhancement of PCE could be due to the high conductivity of the alloyed (Cu2SnS3)0.7(ZnS)0.3 QDs and suitable energy level alignment between the corresponding QDs and perovskite layer. In addition, the PSCs based on the alloyed (Cu2SnS3)0.7(ZnS)0.3 possess superior stability compared with that of the Cu2SnS3 based devices. This work displays that (Cu2SnS3)0.7(ZnS)0.3 QDs can be used as a novel inorganic hole transport material to PSCs.

Dual Role of Cu‐Chalcogenide as Hole‐Transporting Layer and Interface Passivator for p–i–n Architecture Perovskite Solar Cell

AbstractInorganic hole‐transport layers (HTLs) are widely investigated in perovskite solar cells (PSCs) due to their superior stability compared to the organic HTLs. However, in p–i–n architecture when these inorganic HTLs are deposited before the perovskite, it forms a suboptimal interface quality for the crystallization of perovskite, which reduces device stability, causes recombination, and limits the power conversion efficiency of the device. The incorporation of an appropriate functional group such as sulfur‐terminated surface on the HTL can enhance the interface quality due to its interaction with perovskite during the crystallization process. In this work, a bifunctional Al‐doped CuS film is wet‐deposited as HTL in p–i–n architecture PSC, which besides acting as an HTL also improves the crystallization of perovskite at the interface. Urbach energy and light intensity versus open‐circuit voltage characterization suggest the formation of a better‐quality interface in the sulfide HTL–perovskite heterojunction. The degradation behavior of the sulfide‐HTL‐based perovskite devices is studied, where it can be observed that after 2 weeks of storage in a controlled environment, the devices retain close to 95% of their initial efficiency.

Vacuum-Assisted Drying Process for Screen-Printable Carbon Electrodes of Perovskite Solar Cells with Enhanced Performance Based on Cuprous Thiocyanate as a Hole Transporting Layer.

Carbon-based perovskite solar cells without a hole transport layer (HTL) are considered to be highly stable and of low cost. However, the deficient interface contact and inferior hole extraction capability restrict the further improvement of the device efficiency. Introducing a hole transporting layer, such as cuprous thiocyanate (CuSCN), can enhance the hole extraction ability and improve the interface contact. However, our further studies indicated that-at a certain temperature-for carbon-based solar cells, in the CuSCN layer, the diffusion of SCN- into the perovskite film would produce more interfacial defects and aggravate nonradiative recombination, thus hindering the carrier transport. We further disclosed the reasons for performance attenuation during the thermal treatment of carbon electrodes, proposed a vacuum-assisted drying process for carbon electrodes to suppress the destructive effect, and finally, achieved an enhanced efficiency for perovskite solar cells with a CuSCN inorganic HTL and screen-printable carbon electrode. Also, the unencapsulated perovskite solar cell demonstrated over 80% efficiency retention after being stored in an ambient atmosphere (45-70% relative humidity (RH)) for over 1000 h and maintained over 85% efficiency retention for 309 h of 1-sun irradiation under a continuous nitrogen flow under open-circuit conditions.

Improving the hole extraction by hexadecylbenzene modification for efficient perovskite solar cells

In highly efficient halide perovskite solar cells (PSCs), nickel oxide (NiOx) have been widely used as an inorganic hole transport layer (HTL). However, the solution-processed NiOx films always have pinholes, along with inferior contact with perovskite layer. Herein, a surfactant of hexadecylbenzene (HAB) was applied to improve the hole extraction from perovskite to NiOx HTL. With the modification of HAB, a high quality perovskite layer was obtained. Due to the enhanced hole extraction, the HAB modified device showed a higher short-circuit current density (JSc ) and a power conversion efficiency of 17.11%. Therefore, this work offers a novel strategy in interfacial engineering for high-efficiency PSCs.

Simulation and optimization studies on CsPbI3 based inorganic perovskite solar cells

Cesium lead iodide (CsPbI3) based perovskite solar cell (PSC) with inorganic electron and hole transport layers is simulated using SCAPS 1D to find optimum performance conditions for an all-inorganic PSC with maximum stability and efficiency. In this study, the absorption spectrum and bandgap of CsPbI3 absorber layer are computed with the help of density functional theory and the resulting spectrum is used as an input for device simulation. Further improvement of device performance is done by optimizing the work function of back electrode, absorber thickness, doping density as well as defect density. Under optimized conditions, a conversion efficiency of 11.99% is obtained with gold (Au) as back contact metal. The efficiency is enhanced to 15.6% for the FTO/ZnO/CsPbI3/CuSbS2/Se configuration, which uses Se instead of Au as back contact metal, indicating the possibility of replacing the expensive Au with Se as back contact metal in PSCs. The photovoltaic performance parameters achieve their maximum value at an absorber thickness of 547 nm and defect and dopant density of 2.07 × 1014 cm−3 and 1 × 1015 cm−3 respectively. The study shows that the PCE of inorganic CsPbI3 based PSCs can be improved significantly by introducing a low cost back contact metal Se and using inorganic transport materials, ZnO and CuSbS2.

Device Modeling and Design of Inverted Solar Cell Based on Comparative Experimental Analysis between Effect of Organic and Inorganic Hole Transport Layer on Morphology and Photo-Physical Property of Perovskite Thin Film.

It is crucial to find a good material as a hole transport layer (HTL) to improve the performance of perovskite solar cells (PSCs), devices with an inverted structure. Polyethylene dioxythiophene-poly (styrene sulfonate) (PEDOT:PSS) and inorganic nickel oxide (NiOx) have become hotspots in the study of hole transport materials in PSCs on account of their excellent properties. In our research, NiOx and PEDOT: PSS, two kinds of hole transport materials, were prepared and compared to study the impact of the bottom layer on the light absorption and morphology of perovskite layer. By the way, some experimental parameters are simulated by wx Analysis of Microelectronic and Photonic Structures (wxAMPS). In addition, thin interfacial layers with deep capture levels and high capture cross sections were inserted to simulate the degradation of the interface between light absorption layer and PEDOT:PSS. This work realizes the combination of experiment and simulation. Exploring the mechanism of the influence of functional layer parameters plays a vital part in the performance of devices by establishing the system design. It can be found that the perovskite film growing on NiOx has a stronger light absorption capacity, which makes the best open-circuit voltage of 0.98 V, short-circuit current density of 24.55 mA/cm2, and power conversion efficiency of 20.01%.

All-Inorganic Quantum Dot Light-Emitting Diodes with Suppressed Luminance Quenching Enabled by Chloride Passivated Tungsten Phosphate Hole Transport Layers.

Although excellent performance such as high efficiency and stability have been achieved in quantum dot (QD)-based light-emitting diodes (QLEDs) possessing an organic/inorganic hybrid device structure, the highly expected all-inorganic QLEDs remain at the bottleneck stage in recent years, resulting from the luminance quenching of QDs caused by inorganic hole transport layer (HTL) and unbalanced charge injection due to large energy barrier for injecting holes from HTL to QDs. Here, it is reported that the solution-processed inorganic environmentally friendly chloride (Cl)-passivated tungsten phosphate (Cl@TPA) films serve as HTL. The incorporation of Clin TPA effectively passivates the oxygen vacancies, which not only avoids the luminescence quenching of QDs by reducing carrier concentration but also facilitates the hole injection from HTL to QDs with a favorable electronic band alignment, thus achieving the record external quantum efficiency of ≈9.27%, among all previous reports about all-inorganic QLEDs. Most importantly, the resulting all-inorganic QLEDs with Cl@TPA exhibit a substantial improvement in the operational lifetime (T50 >105 h under an initial luminance of 100cdm-2 ), which is almost 30-fold higher than the devices with TPA HTL. This work furnishes a promising strategy for highly efficient and stable QLEDs based on inorganic device structure.

Stable and efficient Sb2Se3 solar cells with solution-processed NiOx hole-transport layer

Sb2Se3 is a promising absorber material for thin-film solar cells owing to its earth-abundant and non-toxic constituents, superior optoelectronic properties, and unique one-dimensional crystal structure. To further increase the power conversion efficiency of the Sb2Se3, we fabricated an n-i-p structure by integrating a solution-processed NiOx hole-transport layer (HTL) into Sb2Se3 solar cells to enhance the carrier collection. In this study, we systematically screen the thickness of NiOx HTL and demonstrate an improved average power conversion efficiency from 6.12% to 7.15% with a 50 nm NiOx HTL. The mechanism associated with the improved device performance was characterized through the microstructure of the material, device physics, and interface electronic behaviors. It is also shown that the low-cost and scalable solution-processed NiOx HTL can improve device stability under an accelerated stress test. Thus, this work paves a way to further improve the performance of antimony chalcogenides-based solar cells via tailoring the inorganic HTL.