Hole Transport Research Articles

High-performance optimization and Analysis of Cs₂CuSbCl₆-Based Lead-Free Double Perovskite Solar Cells with theoretical efficiency exceeding 27%

The primary challenges in photovoltaic solar energy include toxicity, stability, and the cost of solar cells. To address these issues, we propose the use of noble metal halide double perovskites, which are lead-free. CS2CuSbCl6 stands out as a popular absorber due to its huge bandgap, high absorption coefficient, and affordable price. Our research analyzes and simulates solar cells with Cs₂CuSbCl₆ as the absorber material, utilizing SCAPS-1D software. Along with AZnO for the electron transport layer (ETL), we assess the material's stability and suggest less expensive substitutes for hole transport materials (HTLs) such as Spiro-OMeTAD, MoO₃, NiO, Cu2O, and CuSCN. Our goal is to find the ideal values for important photovoltaic parameters to increase the efficiency of the suggested solar cells. This entails examining how the thickness, temperature, and doping level affect the properties of the solar cell. Furthermore, numerous feasible back electrodes are investigated and their impact on performance is assessed to replace the pricey gold (Au) electrode. We discovered that the optimal configuration for Cs2CuSbCl6 is C (metal back contact)/MoO3 (HTM)/Cs2CuSbCl6 (Absorber)/AZnO (ETM)/FTO, resulting in 300 K performance. PCE: 27.56%, Voc: 1.47 V, Jsc: 20.66 mA/cm2, and FF 89.83%.

Strategic design and evaluation of charge transport layers for high-efficiency lead-free BeSiP2-based perovskite solar cells: A careful examination into electron and hole transport layers

Strategic design and evaluation of charge transport layers for high-efficiency lead-free BeSiP2-based perovskite solar cells: A careful examination into electron and hole transport layers

Constructing n/n- Type Perovskite Homojunctions to Achieve High-Efficiency and Stable Printable Mesoscopic Perovskite Solar Cells.

In recent years, carbon-based printable mesoscopic perovskite solar cells (p-MPSCs) without hole transport layers have garnered considerable interest because of their outstanding benefits in terms of stability and cost. However, the use of carbon electrodes instead of hole transport materials and noble metal electrodes leads to energy level mismatch, which limits the power conversion efficiency (PCE) of p-MPSCs. In this work, a molecular doping strategy is proposed employing cyclopentylmethanamine to passivate surface and subsurface crystal defects in perovskite layers while inducing an energy shift toward the p-type in the perovskite region within carbon electrodes. This approach facilitates the formation of a perovskite homojunction at carbon micro-interfaces between carbon electrodes and perovskites. Results demonstrate that the formation of this homojunction optimizes the internal energy level alignment of devices, thereby increasing driving force for hole transfer to carbon electrodes. Ultimately, the devices optimized through this strategy increase the PCE from 17.50% to 19.50% while retaining over 92% of the initial PCE after over 150 days in air ambiance. This study provides a straightforward and effective approach for designing high-efficiency and stable p-MPSCs.

Microlithography of hole transport layers for high-resolution organic light-emitting diodes with reduced electrical crosstalk

Microlithography of hole transport layers for high-resolution organic light-emitting diodes with reduced electrical crosstalk

Over 19.2% Efficiency of Layer‐By‐Layer Organic Photovoltaics by Ameliorating Exciton Dissociation and Charge Transport

AbstractLayer‐by‐layer (LbL) organic photovoltaics (OPVs) are fabricated with polymer PM1 as donor and small molecule L8‐BO as acceptor by employing sequential spin‐coating technology. The small molecule BTP‐eC9 and polymer PTAA are deliberately selected for individually incorporating into PM1 layer and L8‐BO layer, resulting in the power conversion efficiency (PCE) increased from 18.22% to 19.23%. The improvement of performance is attributed to the synergistically increased short circuit current density (JSC) of 27.78 mA cm−2 and fill factor (FF) of 78.23%. The introduction of BTP‐eC9 into PM1 layer can promote the photogenerated exciton dissociation, especially for the excitons near the anode. Meanwhile, molecular crystallinity of PM1 is also enhanced by incorporating appropriate BTP‐eC9 into PM1 layer. The incorporation of PTAA into L8‐BO layer can provide hole transport channels to effectively improve the transport of holes generated by the self‐dissociation of L8‐BO, resulting in the enhanced FFs from 77.40% to 78.23%. The synergistic effects of BTP‐eC9 and PTAA incorporation in donor and acceptor layers result in a 19.23% PCE of the optimized LbL‐OPVs. This work demonstrates that there is great room to hierarchically optimize donor and acceptor layers for achieving highly efficient LbL‐OPVs.

Salutary impact of spontaneous oxidation in CH3NH3SnI3 on CZTS-based solar cell

From the time of discovery, CH3NH3SnI3 has been a promising candidate in photovoltaics due to its outstanding optoelectronic properties. However, stabilization was not easy to achieve in CH3NH3SnI3-based solar cells. Because CH3NH3SnI3 was used as an absorber, its naturally-occurring self-doping property spontaneously modified band alignment, which increased carrier recombination and decreased the efficiency of solar cell gradually. In this paper, for the first time, we have presented detailed study on use of CH3NH3SnI3 as a hole transport layer in prototype solar cell having configuration: CH3NH3SnI3/CZTS/CdS/ZnO/AZO, using SCAPS software. To understand the effect of spontaneous self-doping property of CH3NH3SnI3 on solar cell performance, the analysis of variation in solar cell performance parameters, band alignment conduction band, valance band, Fermi levels, charge density, current density, conductance, capacitance and recombination rate was performed as a function of increasing CH3NH3SnI3 carrier concentration. It was found that, when used as an hole transport layer, the inherent self-doping property of CH3NH3SnI3 became a helpful trait to increase hole extraction and spontaneously enhanced our device efficiency. Thus, the inherent self-doping property of CH3NH3SnI3 transformed from curse to boon when we leveraged CH3NH3SnI3 as an hole transport layer in our solar cell device.

Laminated Two-Terminal All-Perovskite Tandem Solar Cells with Transparent Conductive Adhesives.

Established sequential deposition of multilayer two-terminal (2T) all-perovskite tandem solar cells possesses challenges for fabrication and limits the choice of materials and device architecture. In response, this work represents a lamination process based on a transparent and conductive adhesive that interconnects the wide-bandgap (WBG) perovskite top solar cell and the narrow-bandgap (NBG) perovskite bottom solar cell in a monolithic 2T all-perovskite tandem solar cell. The transparent conductive adhesive (TCA) layer combines Ag-coated poly(methyl methacrylate) microspheres with an optical adhesive. The TCA is employed as a recombination junction, achieving self-encapsulation with high transparency and good conductivity. A high vertical electrical conductivity is realized by optimizing the distribution of microspheres using a novel solidification strategy that employs UV curing and drying at 85 °C at low pressure. In addition, uniform and dense bilayer hole transport layers are realized by vapor-phase evaporation, which facilitates the application of the TCA and achieves pinhole-free buried interfaces in both the WBG perovskite top solar cell and the NBG perovskite bottom solar cell. Using these two strategies, losses in fill factor (FF) and open-circuit voltage (VOC) of the 2T all-perovskite tandem solar cell are reduced, achieving a respectable power conversion efficiency up to 18.2% for the lamination of the all-perovskite tandem solar cell. The laminated tandem solar cell retains ∼93% of initial efficiency after exposure in ambient air (30-70 RH% and 20-35 °C) for ∼30 days.

Oligomeric Carbazole Phosphonic Acid as Hole‐Transporting Layer for Organic Solar Cells With Efficiency of 19.63%

AbstractA class of self‐assembly monolayers, distinguished by a carbazole‐conjugated backbone pendant with phosphonic acid (PA) side units, are widely used as hole‐transporting layers (HTL) in organic solar cells (OSCs). However, challenges such as pronounced aggregation tendency and low conductivity have hindered their widespread applications. This study addresses these limitations by introducing novel oligomeric PA designs to overcome the drawbacks associated with monolayer HTLs. The newly synthesized oligomer integrates carbazole backbones and PA side units through Suzuki polymerization, showing absorption characteristics similar to small molecules, but with reduced aggregation and improved hole transport properties. OSCs using such a HTL achieve an impressive efficiency of 19.63% with remarkable stability. These results highlight the potential of oligomeric HTLs as promising materials for realizing efficient OSCs.

2D/3D heterojunction engineering for hole transport layer-free carbon-based perovskite solar cells.

Hole transport layer (HTL)-free carbon-based perovskite solar cells (C-PSCs) own outstanding potential for commercial applications due to their attractive advantages of low cost and superior stability. However, the abundant defects and mismatched energy levels at the interface of the perovskite/carbon electrode severely limit the device efficiency and stability. Constructing a 2D layer on the surface of 3D perovskite films to form 2D/3D heterojunctions has been demonstrated to be an effective method of passivating surface defects and optimizing the energy level alignment in almost all kinds of PSCs. Due to the unique structure of HTL-free C-PSCs, 2D/3D heterojunctions play especially important roles. This review article summarizes the reports of 2D/3D perovskite heterojunctions in HTL-free C-PSCs. It describes the contributions of 2D/3D heterojunctions in terms of their roles in defect passivation, energy level optimization, and stability improvement. Finally, challenges and prospects of 2D/3D heterojunction for further development of HTL-free C-PSCs are highlighted.

InGaN multiquantum wells—problem of carrier injection

This study addresses the issue of effective carrier injection to quantum wells in laser diode structures. The nitride light emitting structures used in this study were fabricated by Metal-Organic Vapor Phase Epitaxy (MOVPE). We developed three distinct sets of samples, with varying quantum barrier thickness, different QWs indium composition and different position relative to the p- and n-sides of the structure. Electroluminescence (EL) and cathodoluminescence (CL) spectra, together with nextnano simulations, were analyzed to investigate the impact of these structural variations on device performance. Our findings revealed that the thickness of the quantum barriers significantly affects the carrier transport and recombination efficiency. Thicker barriers impede hole transport to the quantum wells (QWs). As a result, light emission is predominantly from the QWs located closer to the p-GaN layer. However, in a well-optimized active region the carrier distribution is uniform, leading to both QWs emitting similar amount of light. We also investigated how different indium compositions in the QWs affect the energy levels and recombination dynamics. Our study showed that in structures with two QWs of different indium content, a small (less than 2%) difference in indium concentration leads to uniform light emission across the wells, while a larger difference concentrates recombination in the deeper well.

Improved Conductivity of 2D Perovskite Capping Layer for Realizing High-Performance 3D/2D Heterostructured Hole Transport Layer-Free Perovskite Photovoltaics.

Perovskite solar cells (PSCs) have emerged as low-cost photovoltaic representatives. Constructing three-dimensional (3D)/two-dimensional (2D) perovskite heterostructures has been shown to effectively enhance the efficiency and stability of PSCs. However, further enhancement of device performance is still largely limited by inferior conductivity of the 2D perovskite capping layer and its mismatched energy level with the 3D perovskite layer. Here, we developed an effective surface modification strategy via synergically incorporating inorganic high valence-state niobium ion (Nb5+) metal dopants and organic ammonium halide salts to in situ construct a high-quality 2D perovskite capping layer on top of the underlying 3D perovskite layer. As a result, the conductivity of the 2D perovskite capping layer was effectively enhanced by 43%, the energy barrier between 3D and 2D perovskite layers was favorably reduced, and the built-in electric field of the 3D/2D heterostructured perovskite stacks has been enlarged. In addition, the 2D perovskite capping layer also effectively reduced the defect densities by up to 29%, as verified by the space-charge-limited-current (SCLC) tests. Benefiting from the facilitated charge extraction and suppressed non-radiative recombination, the blade-coated hole transport layer-free PSCs based on this optimized 3D/2D heterostructured perovskite film achieved an efficiency of 23.2%, ∼19% higher than that of the control device (19.5%), which represented one of the best-performing PSCs with simplified device architecture fabricated via a scalable fabrication technique. The modified 3D/2D perovskite-based device also exhibited improved operational stability.

A Review of Perovskite-Based Solar Cells over the Last Decade: The Evolution of the Hole Transport Layer and the Use of WO3 as an Electron Transport Layer

A Review of Perovskite-Based Solar Cells over the Last Decade: The Evolution of the Hole Transport Layer and the Use of WO3 as an Electron Transport Layer

Fluorene-Terminated π-Conjugated Spiro-Type Hole Transport Materials for Perovskite Solar Cells

Fluorene-Terminated π-Conjugated Spiro-Type Hole Transport Materials for Perovskite Solar Cells

Bipolar Solid-Solution Hosts for Efficient Crystalline Organic Light-Emitting Diodes.

Crystalline organic semiconductors, recognized for their highly ordered structures and high carrier mobility, have emerged as a focal point in the field of high-performance optoelectronic devices. Nevertheless, the intrinsic unipolar properties, characterized by imbalanced hole and electron transport capabilities, have continuously represented a significant challenge in the advancement of high-performance crystalline thin-film organic light-emitting diodes (C-OLEDs). Here, a bipolar solid-solution thin film with a maintained crystal structure has been fabricated using 2-(4-(9H-carbazol-9-yl)phenyl)-1(3,5-difluorophenyl)-1H-phenanthro [9,10-d]imidazole (2FPPICz) and 4-(1-(3,5-difluorophenyl)-1H-imidazo[4,5-f][1,10]phenanthrolin-2-yl)-N,N-diphenylaniline (2Fn) via a weak epitaxial growth (WEG) process, exhibiting nearly equivalent hole and electron mobilities (10-2-10-1 cm2 V-1 s-1). We have demonstrated a blue C-OLED that achieves high efficiency while maintaining low-efficiency roll-off, employing the bipolar solid-solution thin film as the crystalline host matrix and 4,4'-bis[2-(4-(N,N-diphenylamino)phenyl)vinyl]biphenyl (DPAVBi) as the doped emitter. This device achieves a maximum external quantum efficiency (EQE) of 4.6% with Commission Internationale de L'Eclairage (CIE) coordinates lying around (0.15, 0.22). Among crystalline light-emitting devices utilizing carrier-balanced transport, this EQE stands as one of the highest recorded values. Notable advancements include enhanced photon emission capabilities, optimized driving voltage (4.0 V @ 1000 cd m-2), and a lower series resistance Joule heat loss ratio (11.8% @ 1000 cd m-2). This research marks a significant stride in modulating the inherent electrical properties of crystalline host materials, offering a novel and efficacious strategy for the advancement of high-performance crystalline OLEDs.

Functionalized Interlayers in Self‐Powered Organic Photodiodes for Enhanced Near‐Infrared Sensing

AbstractThere is a growing interest in fabricated organic material‐based photodiodes (OPDs) since they are lightweight, flexible, and cost‐effective to manufacture. Notably, they exhibit near‐infrared photo‐sensing capabilities that are self‐powered, a feature attributed to the tunable optical properties of organic semiconductor (OSC) materials. Nonetheless, the application of OPDs in the semiconductor industry encounters challenges compared to their inorganic counterparts, such as low sensitivity and limited durability. In this study, a self‐powered OPD using a poly[4,8‐bis(5‐(2‐ethylhexyl)thiophen‐2‐yl)benzo [1,2‐b:4,5‐b′]dithiophene‐2,6‐diyl‐alt‐(4‐(2‐ethylhexyl)‐3‐fluorothieno[3,4‐b]thiophene‐)‐2‐carboxylate‐2‐6‐diyl)]:biaxial active layer of phenyl‐C70‐butyric acid methyl ester (PTB7‐Th:PC70BM) and an organic hole transport layer (HTL) composed of poly(3,4‐ethylenedioxythiophene) and poly(styrene sulfonate) (PPY:PSS) is developed. These results highlight the effectiveness of PPY:PSS as an HTL, demonstrating distinct improvements in efficiency, photosensitivity, photo‐detectivity, and operational stability of the OPD when the weight ratio between the PPY and PSS is 1:2.

Boosting Efficiency in Flexible Perovskite Solar Cells with Novel HTLs and ETLs: A drift‐diffusion numerical study of CBz‐PAI Interlayers and MXene Back Contacts

AbstractIn this study, the functioning of flexible perovskite solar cells (FPSCs) is examined using drift‐diffusion SCAPS‐1D simulations under ideal conditions. The focus is on the CBz‐PAI interlayer at the perovskite and hole transport layer (HTL) interface and the impact of innovative materials for HTLs, electrons transport layers (ETLs), and transparent conduction electrodes (TCOs), such as AZO and MXene, in the front and back contacts. Initially, 50 configurations of ETLs, including BaZrS3, SnS2, STO, WS2, and ZrS2, as well as HTLs such as ACZTSe, CuBiS3, CZGS, and D‐PBTTT‐14, are tested to identify optimal architecture for enhancing device efficiency. The incorporation of the CBz‐PAI interlayer effectively reduces interfacial charge recombination, minimizing VOC losses and boosting overall performance. After further optimization and the integration of MXene as a back contact, the final FPSC design (PET/ITO/AZO/ZrS2/(FAPbI3)0.77(MAPbBr3)0.14(CsPbI3)0.09/CBz‐PAI/CZGS/MXene‐V3C2F2) achieves an impressive PCE of 27.17%, setting a new benchmark for FPSC efficiency.

Blue Electroluminescent Carbon Dots Derived from Victorian Lignite.

Carbon dots (CDs) derived from natural products have attracted considerable interest as eco-friendly materials with a wide range of applications, such as bioimaging, sensors, catalysis, and solar energy harvesting. Among these applications, electroluminescence (EL) is particularly desirable for light-emitting devices in display and lighting technologies. Typically, EL devices incorporating CDs feature a layered structure, where CDs function as the central emissive layer, flanked by charge transport layers and electrodes. Under an applied external bias, electrons and holes are introduced into the active CD layer, resulting in EL through radiative recombination. However, achieving EL with natural product-derived CDs has remained elusive due to challenges such as production difficulties and quenching in the solid state. In this study, we present, for the first time, the successful realization of EL from natural product-derived CDs, synthesized using Victorian lignite through a straightforward single-step pyrolysis method. The CDs demonstrated excellent dispersibility in solvents, allowing them to serve as an emissive layer in light-emitting diodes (LEDs). This was achieved by spin-coating a concentrated CD solution between the organic hole and electron transport layers on a glass substrate coated with indium tin oxide. Remarkably, the CDs retained their dispersibility and emissive efficiency both in solution (toluene) and after film formation. Moreover, the resulting LED demonstrated blue EL, characterized by a peak emission at 460 nm and a maximum luminance of 100.4 cd/m2. This luminance is comparable to that achieved with CDs synthesized from conventional chemical carbon sources. These results highlight the promise of natural product-derived CDs as sustainable and eco-friendly materials for use in LED applications.

Photothermally Cross-Linkable Polymeric Hole Transport Material Functionalized with Azide for High-Performance Quantum Dot Light-Emitting Diodes.

Poly[(9,9-dioctylfluorenyl-2,7-diyl)-alt-(4,4'-(N-(4-butylphenyl)))] (TFB) is a widely used hole transport material (HTM) in quantum dot light-emitting diodes (QLEDs). However, TFB-based solution-processed QLEDs face several challenges, including interlayer erosion, low hole mobility, shallow energy level of the highest occupied molecular orbital, and current leakage, which compromise the device efficiency and stability. To overcome these challenges, bromine and azide-based photothermally cross-linkable TFB derivatives, i.e., TFB-Br and TFB-N3, were designed and synthesized. TFB-N3 photothermally cross-linked under 254 nm ultraviolet light at 140 °C exhibited excellent solvent resistance within 30 s. Furthermore, the photothermally cross-linked TFB-N3 formed a compact three-dimensional (3D) network in QLEDs, enhancing hole transport and reducing the leakage current. Moreover, the HOMO energy level in photothermally cross-linked TFB-N3 decreased to -5.39 eV from that in TFB (-5.30 eV), reducing the hole transport energy barrier. Thus, the charge balance in the quantum dot (QD) layer was enhanced, and the current leakage was reduced, improving the overall QLED performance. The photothermally cross-linked TFB-N3-based QLEDs achieved a maximum external quantum efficiency of 19.53%, i.e., 61% higher than that of devices using TFB. Moreover, the T90 lifetime of the photothermally cross-linked TFB-N3-based QLEDs was 4.49 times longer than that of TFB-based devices. The proposed strategy demonstrates that incorporating azide groups into polymeric HTMs can considerably enhance their hole transport and solvent resistance and reduce leakage current, improving QLED efficiency and stability.

Graphene quantum dots as hole transport material in lead free perovskite solar cell: a SCAPS-1D numerical study

Graphene quantum dots as hole transport material in lead free perovskite solar cell: a SCAPS-1D numerical study

Improvement of Lead-Free Bismuth Based Perovskite Solar Cell Efficiency with Graded Bandgap Structure

Lead (Pb) halide perovskite has been identified as a promising light-harvesting material for perovskite solar cells (PSCs) with power conversion efficiency (PCE) exceeding 26%. However, the toxicity of Pb-based materials and poisonous environment are the main hindrances that limit their reliable applications. Bismuth (Bi)-based perovskite has shown high potential to replace conventional Pb-based perovskite, but the PCE of Bi-based perovskite solar cells is far lower than Pb-based. Despite the early exploration of Bi-based materials, a fundamental understanding of the material properties and developing strategies, including device design to improve performance, are needed immediately. Here, we report the graded bandgap design for Bi-halide PSCs, which aims to enhance the output current and PCE by maximizing the solar spectrum through device architecture. Titanium dioxide (TiO2) was used as an electron transport layer (ETL), and Spiro-OMeTAD was used as a hole transport layer (HTL) due to its facile implementation and high performance in electronic devices. The variation of iodine concentration in bi-doped iodide sets up bandgap tuning and the conductivity type of the layer. This conFigureuration produces cells with desirable performance that effectively absorb the photons in almost all parts of the solar spectrum. Both open circuit voltage (Voc) (940 mV) and fill factors (~58%) for the best cells have shown drastic improvement over single active layer device, and the short current densities (Jsc) measured are in the range (20-30) mAcm-2. The effects of quasi-electric fields instigated by the graded bandgap structure in the active layers upon the illumination current density and open-circuit voltage of a solar cell will be discussed further.