Hole Transport Layer Material Research Articles

Graphene oxide-titanium oxide-polyaniline hybrid materials for high-performance dye-sensitized solar cells

A new solar cell that comprises a graphene oxide and titanium oxide nanoparticle (NP) composite with graphitized polyaniline (PANI) has been tested in polymer solar cells (PSCs). In this study, a series of conjugated polymers were synthesized and evaluated as the absorber and hole-transport layer materials in organic solar cells, demonstrating the significant impact of the chemical structure of the polymers on solar cell performance. The incorporation of graphene oxide (GOX) and titanium oxide TiO2 NP in conjugated polymers, particularly when graphitized within the PANI layer, led to improved open-circuit voltages compared to structurally similar polymers without NP. The morphology of the composite films was analyzed and related to the photovoltaic performance of polymers synthesized with polyaniline PANI-base and PANI-salt. Optimal NP addition in PANI-salt, PANI-base, PANI-base-TiO2, and PANI-base-GOX resulted in open-circuit voltages and efficiencies of 433 mV and 3.67%, 250 mV and 0.595%, 310 mV and 1.358%, and 520 mV and 2.366%, respectively. This study underscores the importance of polymer film uniformity in the performance of PSCs, with the highest efficiency obtained using a conjugated polymer with the best PANI-salt and PANI-base-GOX films. The research sheds light on the relationship between polymer structure and device photovoltaic performance, which is crucial for the design of new polymeric materials for efficient use and stable OSCs and PSCs.

Design and optimization of high-performance eco-friendly perovskite solar cells: Utilizing FAMASnGeI3 and CsGeI3 as absorbers and tuning HTL and interface parameters

In this work, several designs of lead-based and lead-free perovskite solar cells (PSCs) have been developed and investigated. For the proposed designs, CH3NH3PbI3 (lead-based), FAMASnGeI3, and CsGeI3 (lead-free) are used as absorber materials, [Formula: see text] and NiO have been used as Hole Transport Layer (HTL) materials and TiO2 as Electron Transport Layer (ETL) materials. ETL materials, in general, have more concern with stability issues and HTL materials have more issues with efficiency improvements. The effect of changing thickness, doping density and defect density of the absorber layer, as well as HTL, defect density of absorber/HTL interface and work functions of front and back contacts on the performance of the proposed devices, are investigated. To enhance the device performance, optimization of the device parameters is performed. After optimization of different parameters, it is observed that the lead-based device structure TiO2/CH3NH3PbI3/NiO has a maximum efficiency of 29.94%. Even the corresponding lead-free device structure TiO2/CsGeI3/NiO exhibits a maximum efficiency of 29.19%. Additionally, this study delved into the influence of altering series and shunt resistances, as well as temperature on the operational characteristics of the lead-free optimized device. Such eco-friendly and cost-effective alternatives as lead-free perovskite cells can be very promising for future work.

Physically‐Deposited Hole Transporters in Perovskite PV: NiOx Improved with Li/Mg Doping

AbstractNickel oxide (NiOx) has received a lot of attention as an inorganic hole transport material (HTM) in perovskite solar cells (PSCs) during the last decade, owing to its high hole mobility, chemical stability, good optical transparency, and suitable energy levels that align with the valance band of the perovskite absorber methylammonium lead iodide (MAPbI3). This study explores Li and Mg co‐doped NiOx thin films physically‐deposited from developed sputtering targets obtained through cold isostatic pressing and sintering. After sputtering, the structural, elemental, morphological, optical, and electrical properties of the layers are investigated by XRD, XPS, SEM, AFM, UV–vis spectrophotometer, and Hall‐effect; revealing that crystalline, homogeneous, and smooth films are obtained. In particular, improvements in mobility and conductivity values are observed with Li and Mg doping, which contribute to enhanced PSC performance when used as an HTM layer in the glass‐indium tin oxide (ITO)/NiOx‐based HTM/MAPbI3/phenyl butryic acid methyl ester (PCBM)/bathocuproine (BCP)/Ag architecture. The champion solar cell achieves PCE of 15.52%. In addition, the average values of all samples are boosted, JSC (from 13.21 to 15.60 mA cm−2) and FF (from 59.32% to 67.7%), relative to pristine HTM, resulting in a pronounced PCE increment of up to 30% with the HTM film sputtered by a single target of co‐doped material.

Counterion Engineering toward High-Performance and pH-Neutral Polyoxometalates-Based Hole-Transporting Materials for Efficient Organic Optoelectronic Devices.

Although protonated polyoxometalates (POMs) are promising hole-transporting layer (HTL) materials for optoelectronic devices owing to their excellent hole collection/injection property, pH neutrality, and noncorrosiveness, POMs are seldom used as high-performance HTL materials. Herein, we designed and synthesized a series of mixed-additive POMs with pH-neutral counterions (NH4+, K+, and Na+) as HTL materials. X-ray photoelectron spectroscopy and single-crystal X-ray analyses indicated that the use of the lacunary heteropolyanion [P2W15O56]12- as an intermediate ensured successful incorporation of the counterions into the mixed-addenda POMs without causing deterioration of the POM frameworks. The hole-transporting layer performance of POM-NH4, which was characterized by a high work function and good conductivity and could be prepared using a low-cost method surpassed those of its protonated counterpart POM-4 and many classic HTL materials. An organic solar cell (OSC) modified with POM-NH4 delivered a power conversion efficiency of 18.0%, which was the highest photovoltaic efficiency achieved by POM-based OSCs to date. Moreover, an HTL material based on POM-NH4 reduced the turn-on voltage of an organic light-emitting diode from 4.2 to 3.2 V. The results of this study suggest that POMs are promising alternatives to the classic HTL materials owing to their excellent hole-collection ability, low costs, neutral nature, and high-chemical stability.

Reducing the Depletion Region Width at the Anode Interface via a Highly Doped Conjugated Polyelectrolyte Composite for Efficient Organic Solar Cells.

In the realm of organic solar cells (OSCs), the width of the depletion region at the anode interface is a critical factor that adversely impacts the open-circuit voltage (Voc) and the power conversion efficiency (PCE). To address this challenge, a novel approach involving a conjugated polyelectrolyte (CPE)-based composite, PCP-2F-Li:POM, has been developed. This composite serves as a solution-processed hole transport layer (HTL), effectively minimizing the depletion region width in high-performance OSCs. The innovative aspect of PCP-2F-Li:POM lies in its "mutual doping" mechanism. Polyoxometalate (POM) is utilized as a dopant, facilitating the formation of p-doped CPE and n-doped POM within the composite. This results in a substantial increase in doping density, nearly 2 orders of magnitude higher than that observed in unmodified CPE. Consequently, the width of depletion region is markedly reduced, shrinking from 76.4 to 6.0 nm. This reduction plays a pivotal role in enhancing hole transport via the tunneling effect. The practical impact of this development is notable. It leads to an increase in Voc from 0.84 to 0.86 V, thereby contributing significantly to an impressive PCE of 18.04% in OSCs. Moreover, the compatibility of PCP-2F-Li:POM with large-area processing techniques underscores its potential as a viable HTL material for future practical applications. Additionally, its contribution to the enhanced long-term stability of OSCs further bolsters its suitability for practical applications.

2D Polymers with Lead Anchoring Groups Enable Perovskite Solar Cells with Over 24% Efficiency

The hygroscopic dopants used in Spiro‐OMeTAD hole‐transport materials (HTMs) in n–i–p perovskite solar cells (PSCs) inevitably cause device degradation. Herein, two polymer interface materials based on lead anchoring groups are developed. It is found that 2D polymers 2DP‐BT and 2DP‐Por can form dense films and exhibit excellent hydrophobicity. Importantly, 2DP‐Por can passivate the surface defects through noncovalent interactions, reducing nonradiative recombination loss. After introducing these polymer interface materials between the perovskite layer and the HTM layer, the optimized devices using 2DP‐Por and 2DP‐BT achieve champion power conversion efficiency of 24.12% and 23.29%, respectively, and the stability is significantly improved. These results indicate that developing polymer interface materials containing lead anchoring groups can improve PSC efficiency and stability and elucidate critical molecular design rules for interface materials.

Numerical simulation and performance optimization of a lead-free inorganic perovskite solar cell using SCAPS-1D

The perovskite solar cells, founded on lead halides, have garnered significant attention from the photovoltaic industry owing to their superior efficiency, ease of production, lightweight characteristics, and affordability. However, due to the hazardous nature of lead-based compounds, these solar cells are currently unsuitable for commercial production. In this context, a lead-free perovskite, cesium-bismuth iodide (Cs3Bi2I9) is considered as a potential alternative to the lead halide-based cell due to their non-toxicity and stability, but this perovskite cannot be matched with random hole transport layer (HTL) and electron transport layer (ETL) materials compared to lead halide-based perovskite because of their crystal structure and band gap. Therefore, in this study, performance comparison of different ideal HTL and ETL materials for Cs3Bi2I9 perovskite layer were studied using SCAPS-1D device simulation on the basis of open circuit voltage, short circuit current, power conversion efficiency (PCE) and fill factor (FF) as well as several novel PSC configuration models were designed that can direct for further experimental research for PSC device commercialization. Results from this investigation reveals that the maximum efficiency of 20.96 % is obtained for the configuration ITO/WS2/Cs3Bi2I9/NiO/Au with optimized parameters such as thickness 400 nm, band gap 2.1eV, absorber layer defect density 1012 cm−3, donor density of ETL 1018 cm−3 and the acceptor density of HTL 1020 cm−3.

Device modelling of tin based perovskite solar cell with distinct hole transport layer material

Device modelling of tin based perovskite solar cell with distinct hole transport layer material

Impact of hole-transport layer materials on the field-induced degradation of p-i-n perovskite solar cells

The choice of hole-transport materials (HTMs) has a strong impact on electric field-induced degradation of perovskite solar cells (PSCs). Rational design of HTMs is necessary to make PSCs sufficiently stable for the targeted practical applications.

Design and performance evaluation of eco-friendly FASnI3/CsSn0.5Ge0.5I3 based perovskite solar cell with distinct charge transport layer: A computational modeling

This article provides a comprehensive analysis and exploration of a novel design approach for Perovskite Solar cells (PVKSC) that incorporates two absorber layers, with a specific focus on their potential applications in energy generation. This research employs a computational modeling approach to conduct a thorough examination of PVKSCs based on FASnI3/CsSn0.5Ge0.5I3. The primary objective of this study is to examine and choose the appropriate materials for the hole transport layer material (HTLM) and the electron transport layer material (ETLM). Additionally, the research aims to identify the optimal parameters for the active thickness layer, trap concentration, energy bandgap, interface trap concentration, and acceptor concentration for PVKSC. Through the optimization of the device's parameters, notable improvements are observed. The power conversion efficiency (PCE) is enhanced to 33.16 %, while the current density (Jsc) experiences an increase to 31.218 mA/cm2. Additionally, the open circuit voltage rises to 1.185 V, and the fill factor demonstrates improvement, reaching 89.58 %. These advancements are achieved by employing Zn3P2 as the HTLM and SnS2 as the ETLM in the design. This research emphasizes the optimistic prospects of lead-free PVKSC and presents novel opportunities for their advancement and utilization in diverse solar contexts.

Improved Light Extraction in Organic Light‐Emitting Diodes via Semiconductor Dilution

AbstractIncreasing the internal light extraction efficiency of organic light‐emitting diodes (OLEDs) is key to improving their performance for solid‐state lighting applications; however, it is challenging to do this in a way that is compatible with high volume manufacturing. Here, it is shown that the outcoupling efficiency of OLEDs can be improved by diluting their hole transport layer (HTL) with the low refractive index material trifluoropropyl oligomeric silsesquioxane (F‐POSS). Specifically, co‐evaporating 40 vol.% F‐POSS in the HTL of single and multi‐stack phosphorescent OLEDs decreases its refractive index by Δn ≈ 0.2, which in turn yields a ≈12% increase in their outcoupling efficiency with no impact on electrical performance or operational lifetime. This result is significant because F‐POSS is a small molecule that sublimes cleanly, does not aggregate, and is compatible with state‐of‐the‐art HTL materials, making it a realistic path to increase light extraction in commercial OLEDs manufactured on existing production lines.

An Alternative to Chlorobenzene as a Hole Transport Materials Solvent for High-Performance Perovskite Solar Cells

Spiro-OMeTAD is a widely used hole-transporting layer (HTL) material, characterized by high hole mobility and good film-forming properties, in perovskite solar cells (PSCs). However, this material has high synthesis costs, low solubility, dependence on hygroscopic dopants, and a low commercial potential. Recently, we investigated alternative materials with good solubility, simple synthetic methods, and good electrical characteristics for use as hole transport materials (HTM) in triple-cation PSCs. Herein, (E,E,E,E)-4,4′,4″,4′″-[Benzene-1,2,4,5-tetrayltetrakis(ethene-2,1-diyl)]tetrakis[N,N-bis(4-methoxyphenyl)aniline], which has a small molecular weight and similar properties to Spiro-OMeTAD, was assessed for use as a HTM via a pre-test of device performance, including its electrical properties, surface morphology, and coating process method, with PSC efficiencies routinely surpassing 20%. A remarkable open-circuit voltage of 1.111, along with a photovoltaic efficiency of 20.18% was obtained in PSCs using this HTM with dichloromethane (DCM) instead of chlorobenzene, indicative of its potential for the fabrication of resistance components with improved surface uniformity. These results provide insights into DCM as an efficient solvent for small molecule-based HTM.

Side-Chain Engineering in Small-Molecule Hole Transport Layer Materials for High-Performance QD-LEDs

Side-Chain Engineering in Small-Molecule Hole Transport Layer Materials for High-Performance QD-LEDs

Red Fluorescent Carbon Dots with Alkyl Chain Achieving Stable Electroluminescence via an In Situ Electric Excitation

AbstractThe energy barrier between the highest occupied molecular orbital (HOMO) of the emission layer (EML) and the hole transport layer material (HTL) restricts the development of carbon dots (CDs) based light‐emitting diodes (LEDs). Here, the fabrication of red fluorescent CDs (RCDs) by a one‐step solvothermal method is reported. These RCDs have a photoluminescence quantum yield (PLQY) of 47.97% and a full width at half maximum (FWHM) of 26 nm. This study also shows the RCDs‐based LEDs fabrication with Poly(9,9‐dioctylfluorene‐co‐N‐(4‐butylphenyl) diphenylamine (TFB) as HTL. In normal case, these devices are not able to work due to the large interfacial energy barrier between RCDs and TFB. While, the RCDs‐LEDs can overcome through interfacial energy barriers and achieve stable carrier injecting by a simple in situ electric excitation at the current of 50 mA cm−2. This work provides a new strategy to overcome the obstacle of mismatch of interfacial energy levels in the LEDs by an in situ electric excitation.

Enhanced efficiency and long-term stability of all inorganic CsPbBr3 perovskite solar cells via regulation of charge separation and extraction by band engineered-Co3O4 nanocrystals as a hole transport material layer

Insertion of an inorganic HTM intermediate at the CsPbBr3/Carbon interface can significantly improve photo-generated holes extraction efficiency without sacrificing advantages in device stability. Herein, low-cost and eco-friendly Co3O4 nanocrystals were synthesized by precipitation method and utilized as efficient inorganic HTM for CsPbBr3 PSCs. By regulating the hole quasi-fermi level (Ef, HTL) of the perovskite film with Co3O4 nanocrystals possessing a lower conduction band (CB), the built-in electric field (BEF) inside the CsPbBr3 can be reinforced, for which the Co3O4-induced energy level reconstruction facilitates fast charge separation and extraction because of the intensified driving force. In addition, the charge recombination behavior can be effectively inhibited. Finally, all inorganic CsPbBr3 PSCs with an architecture of FTO/c-TiO2/m-TiO2/CsPbBr3/Co3O4/carbon PSC realizes efficiency of 8.92% with an open-circuit voltage (Voc) of 1.531 V. Furthermore, the unencapsulated Co3O4-based PSC exhibits excellent stability in ambient air, keeping 98% of its initial efficiency after 90 days in 80% high humidity condition, and 97% of initial efficiency after 40 days in a high-temperature atmosphere of ∼80 °C.

Inhibiting hysteresis and optimizing the performance of perovskite solar cells

We developed a comprehensive Poisson and drift-diffusion solver coupled with a time-dependent ion migration model in the COMSOL simulation software to analyze hysteresis effects and efficiency in perovskite solar cells (PSCs). Initial simulations on PSCs with the structure ITO/SnO2/CH3NH3PbI3/Spiro-OMeTAD/Au revealed suboptimal efficiency of 10.31% due to hysteresis loops near the open-circuit voltage (Voc) caused by interface recombination. Next, we explored the influence of the transport layer's dielectric constant on PSCs performance and hysteresis. The modeling results emphasized the vital role of the transport layer's dielectric constant in determining PSCs hysteresis and power conversion efficiency (PCE). To investigate further, we replaced the hole transport layer (HTL) material with NiO, CuSCN, and CuI. Studied four different transport layer combinations for n-i-p PSCs: SnO2-Spiro-OMeTAD, SnO2–NiO, SnO2–CuSCN, and SnO2–CuI. Notably, the SnO2–CuSCN combination achieved an impressive efficiency of 21.30%. The p-i-n PSCs with a matched dielectric constant PCBM-PTAA transport layer combination achieves higher PCE. It attains a reverse-scan PCE of up to 21.22% with a fill factor (FF) of 85.04%. Our findings underscore the importance of dielectric constant matching in both electron transport layer (ETL) and HTL, highlighting the potential of SnO2–CuSCN and PCBM-PTAA as transport layer materials for achieving high efficiency and minimizing hysteresis in PSCs.

Designing next-generation kesterite solar cells: A systematic numerical investigation of innovative structures and design variants for enhanced photovoltaic performance

This paper presents a thorough numerical investigation of copper zinc tin sulfide (CZTS)-based solar cells utilizing the SCAPS-1D simulation tool. In light of the scarcity of indium and gallium, CZTS is explored as a promising alternative absorber material. The study encompasses an extensive array of 280 device simulations, including a systematic optimization process targeting enhanced power conversion efficiency (PCE). Notably, this iterative optimization procedure results in a notable PCE increase from 11.01% to 14.24%. By delving into the realm of electron transport layer (ETL) materials, the integration of a CdO layer culminates in a significant PCE milestone of 15.71%, and a new structure was extrapolated from this step Back contact/CZTS/CdO/ZnO. Furthermore, an exploration involving 172 diverse configurations incorporating various hole transport layer (HTL) materials unveils a remarkable peak PCE of 21.14% (Back contact/SnS/CZTS/CdSe/ZnO). These findings provide valuable insights and directives for the advancement and optimization of CZTS-based solar cells.

Incorporation of carbon quantum dots with PEDOT:PSS for high-performance inverted organic solar cells

Inverted organic solar cells (iOSCs) have attracted considerable attention because of their ease of fabrication and suitability for roll-to-roll processing. Poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS), with multiple favorable properties, is the most actively studied hole-transporting layer (HTL) material. However, the pristine state of PEDOT:PSS is limited by its inefficient, poor, and inhomogeneous conductivity. Herein, we demonstrate strategies to enhance the performance of iOSC devices by introducing carbon quantum dots (CQDs), which have controllable conductivity and band edges, into the PEDOT:PSS HTL. This is considered to be an efficient route for modifying the intrinsic properties and electrical conductivity of PEDOT:PSS. The CQDs were first synthesized through a microwave-assisted process by employing eco-friendly and low-cost material sources. By optimizing the ratio of CQDs incorporated into PEDOT:PSS (PH-G0.05), an iOSC with a remarkable enhancement of 3.90% in power conversion efficiency, was obtained. Using PH-G0.05 HTL helped to improve the contact quality and assisted the hole extraction/transport ability at the photoactive/top Ag anode interface with high electrical conductivity (2.80 S cm–1), good surface morphology (RMS = 7.34 nm), and suitable work function (4.78 eV). Our efforts to develop a solution process for CQDs-incorporated PEDOT:PSS HTLs shows considerable promise for the potential replacement of vacuum-based methods in iOSC applications.

Comparative Simulation Study of the Performance of Conventional and Inverted Hybrid Tin-Based Perovskite Solar Cells

A hybrid tin-based (GA0.2FA0.78SnI3-1% EDAI2) perovskite solar cell (PSC) with a p-i-n inverted structure has been reported to pass all the rigorous standard tests successfully and achieve a certified power conversion efficiency (PCE) of 8.3%. Our previous numerical study showed that this PCE could be considerably increased to 24.1% by engineering and controlling the interfaces of the cell. The aim of the current study is to compare the performance of a conventional n-i-p structure with its inverted p-i-n analog quantitatively, and demonstrate that, by improving the conventional structure, it can achieve a PCE score approximately equal to the inverted p-i-n structure. To that end, the absorber layer was chosen to be GA0.2FA0.78SnI3-1% EDAI2, while four ETL (electron transport layer) materials (TiO2, WS2, SnO2, and ZnOS), and four HTL (hole transport layer) materials (PEDOT:PSS, Cu2O, CuSCN, and CuI) were considered. Most used ETL/HTL combinations have been rigorously investigated with the aim of finding the ultimate configuration, providing the highest photovoltaic properties. Additionally, the effect of the layers’ thicknesses and their doping concentrations were inspected, and their impact on the photovoltaic properties of the PSC was investigated. The optimized structure with CuI (copper iodide) as the HTL and ZnOS (zinc oxysulphide) as the ETL scored a PCE of 24.1%, which is comparable to the value found with the inverted structure (26%). The current numerical simulation on GA0.2FA0.78SnI3-1% EDAI2 could be considered as a milestone in its chances for commercial development.

Two-Dimensional Graphitic Carbon Nitride for Improving the Performance of Organic Solar Cells.

Organic solar cells (OSCs) have attracted lots of attention owing to their low cost, lightweight, and flexibility properties. Nowadays, the performance of OSCs is continuously improving with the development of active layer materials. However, the traditional hole transport layer (HTL) material Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) presents insufficient conductivity and rapid degradation, which decreases the efficiency and stability of OSCs. To conquer the challenge, the two-dimensional (2D) graphitic carbon nitride (g-C3N4) nanomaterials incorporated into the PEDOT:PSS as hybrid HTL are reported. The addition of g-C3N4 into PEDOT:PSS enables the thickness of the HTL to decrease for enhancing the transmittance of the film and increase the conductivity of PEDOT:PSS. Thus, the device exhibts improved charge transport and suppressed carrier recombination, leading to the increase in short-circuit current density and power conversion efficiency of the devices. This work demonstrates that the incorporation of 2D g-C3N4 into PEDOT:PSS for D18:Y6 and PM6:L8-BO-based OSCs can significantly improve the device efficiency to 17.48% and 18.47% with the enhancement of 7.04% and 8.46%, respectively.