Composite Hole Transport Layer Research Articles

Enhanced performance of perovskite light-emitting diodes with PEDOT:PSS/CsBr composite hole transport layer

Perovskite light-emitting diodes (PeLEDs) are widely used in optoelectronics due to their excellent performance. The hole transport layer (HTL) plays a crucial role in the performance of the device. In this paper, we prepared quasi-two-dimensional perovskite light-emitting diodes with doping CsBr into PEDOT:PSS as a composite HTL, and investigated the optoelectronic properties of the devices. The maximum luminance of the CsBr-doped device was 6652 cd/m2 and the maximum current efficiency (CE) was 7.55 cd/A, which were increased by 112 % and 80 % compared with the undoped device, respectively. This is primarily due to the PEDOT:PSS/CsBr composite HTL optimizes the morphology of the perovskite film, passivates the defects of the perovskite film, and suppresses the exciton quenching at the HTL/perovskite emission layer (EML) interface. Meanwhile, CsBr doping helps to enhance the hole transport ability of HTL and thus increase the exciton recombination efficiency, which improves the device performance. The results in this paper can provide experimental support for the development of PeLEDs.

Suppressing Trap‐Assisted Nonradiative Recombination via Interface Modification for Achieving Efficient Organic Solar Cells

AbstractTrap states in organic solar cells (OSCs) can capture free charges, leading to a reduction in current density and significant energy loss. Since charge collection is primarily dependent on the interface layer, minimizing trap states at interfaces can effectively suppress energy losses, a topic that has been rarely explored. Herein, an interface strategy is proposed by combining Me‐4PACz and PEDOT:PSS to mitigate the trap‐assisted nonradiative recombination at the hole transport layer (HTL). OSCs based on the Me‐4PACz/PEDOT:PSS exhibit reduced trap densities and low energy losses compared to devices fabricated with a single‐layer HTL. This reduction can be attributed to a lower nonradiative recombination rate during hole transport at the interface. Changes in the work function of the two interlayers due to contact result in the existence of a built‐in potential inside the composite interlayer, promoting charge collection and reducing energy loss from charge recombination. Furthermore, the composite HTL interface induces vertical phase separation of active layer, leading to significant improvements of the fill factor for OSCs. As a result, high power conversion efficiencies (PCEs) of 18.70% and 19.02% are achieved for binary all‐polymer solar cells and polymer donor/small molecule acceptor solar cells, respectively.

Chemisorption-Induced Robust and Homogeneous Tungsten Disulfide Interlayer Enables Stable PEDOT-Free Organic Solar Cells with Over 19% Efficiency.

Construction of a high-quality charge transport layer (CTL) with intimate contact with the substrate via tailored interface engineering is crucial to increase the overall charge transfer kinetics and stability for a bulk-heterojunction (BHJ) organic solar cell (OSC). Here, we demonstrate a surface chemistry strategy to achieve a homogeneous composite hole transport layer (C-HTL) with robust substrate contact by self-assembling two-dimensional tungsten disulfide (WS2) nanosheets on a thin molybdenum oxide (MoO3) film-evaporated indium tin oxide (ITO) substrate. It is found that over such a well-defined C-HTL, WS2 is homogeneously tethered on the ITO/MoO3 substrate stemming from the strong electronic coupling interaction between the building blocks, which enables a favorable interfacial configuration in terms of uniformity. As a result, the D18:L8-BO-based OSC with C-HTL exhibits a power conversion efficiency (PCE) of 19.23%, an 11% improvement over the WS2-based control device, and the highest efficiency among single-junction PEDOT-free binary BHJ OSCs.

A regulation strategy of self-assembly molecules for achieving efficient inverted perovskite solar cells.

Self-assembled monolayers (SAMs) have been successfully employed to enhance the efficiency of inverted perovskite solar cells (PSCs) and perovskite/silicon tandem solar cells due to their facile low-temperature processing and superior device performance. Nevertheless, depositing uniform and dense SAMs with high surface coverage on metal oxide substrates remains a critical challenge. In this work, we propose a holistic strategy to construct composite hole transport layers (HTLs) by co-adsorbing mixed SAMs (MeO-2PACz and 2PACz) onto the surface of the H2O2-modified NiOx layer. The results demonstrate that the conductivity of the NiOx bulk phase is enhanced due to the H2O2 modification, thereby facilitating carrier transport. Furthermore, the hydroxyl-rich NiOx surface promotes uniform and dense adsorption of mixed SAM molecules while enhancing their anchoring stability. In addition, the energy level alignment at the interface is improved due to the utilization of mixed SAMs in an optimized ratio. Furthermore, the perovskite film crystal growth is facilitated by the uniform and dense composite HTLs. As a result, the power conversion efficiency of PSCs based on composite HTLs is boosted from 22.26% to 23.16%, along with enhanced operational stability. This work highlights the importance of designing and constructing NiOx/SAM composite HTLs as an effective strategy for enhancing both the performance and stability of inverted PSCs.

Ti3C2Tx MXene‐Assisted CuBO2 Hole Transport Layer for High‐Performance Ultraviolet Photodetectors

AbstractThe efficient separation and extraction of holes can be attributed to the favorable properties possessed by the hole transport layer (HTL). Herein, a novel solution‐processable hybrid HTL based on CuBO2 and Ti3C2Tx MXene (CuBO2@MXene) is developed to enhance the performance of ultraviolet photodetectors (UV PDs). By optimizing the ratio of Ti3C2Tx MXene to CuBO2, the optimized responsivity and detectivity of the UV PDs based on the composite HTL have achieved 184 mA W−1 and 2.88 × 1013 cm Hz1/2 W−1 in self‐powered mode, respectively, and even up to 3.25 × 104 mA W−1 at −1.5 V. This significant improvement in device performance can be attributed to the interlaced architecture of CuBO2@MXene, which ameliorates hole mobility and charge extraction capability while reducing the trap state density of the HTL. The built‐in electric field of the TiO2/CuBO2 heterojunction is strengthened by the incorporation of Ti3C2Tx MXene, thereby significantly reinforcing the photovoltaic effect. Moreover, the lower thermal conductivity of CuBO2@MXene suppresses its pyroelectric effect, weakening the blocking effect of the thermoelectric potential on hole transport and ultimately leading to a remarkable boost in the output current. These results indicate the promising potential of the hybrid CuBO2@MXene HTL for constructing high‐performance optoelectronic devices.

PEDOT:PSS doping strategy of improving both interface energy level matching and photocarrier transport in FASnI3 perovskite solar cells

Tin-based perovskite solar cells (PSCs) have been the focus of substantial research globally as a promising choice for lead-free PSCs. Sn-based PSCs performance, however, the performance of PSCs is still significantly inferior to that of lead-based PSCs. The disparity between the energy band levels of the perovskite absorber and charge transport layers, as well as the chemical instability of Sn halide perovskite crystals, are the primary constraints in this regard. Herein, potassium chloride (KCl) was added to polymer poly (3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) to improve the ability to transport holes and match energy levels. The formamidinium tin triiodide based PSCs constructed on KCl-doped PEDOT:PSS has a 5.9 % power conversion efficacy with a low hysteresis, which is comparatively higher than of the control devices (4.3 %). The improvement in photovoltaic performance has been predominantly attributed to two effects, specifically; PEDOT: PSS conductivity and hole extraction, both of which improved following KCl doping. More intriguingly, the modified device exhibit increased open-circuit voltage due to the downshift of PEDOT:PSS energy level by KCl doping. The composite hole transport layer strategy described in this paper provides a means for energy level adjustment and charge transport to enhance the performance of Sn-based PSCs.

Construction of perovskite solar cells and X-ray detectors using the indium selenide-carbon nanotube hybrids tuned hole transporting layer

Recently, two-dimensional (2D) materials have fascinated consideration in optoelectronic outcomes because of their remarkable electronic configurations. Herein, ultrasonic reduction process was employed to prepare the indium selenide@carbon nanotube (In2Se3@CNT) hybrid with different amounts (10, 20 and 30%) of CNT particles. The morphological and structural properties authorized the formation of In2Se3 and their CNT hybrid. Further, spin casting was engaged to form the In2Se3@CNT/PEDOT:PSS hybrid film as an anode interfacial layer for the perovskite based solar cell and X-ray detecting devices. The consequences showed the maximum power conversion efficiency (PCE) of 13.36% by introducing the In2Se3@CNT (20%)/PEDOT:PSS composite hole transport layer into the solar cell. On the other hand, the fabricated X-ray photodetector with In2Se3@CNT (20%)/PEDOT:PSS hole interfacing layer attained a superior sensitivity of 4.48 mA/Gy·cm2. The improved device function credited to the increase of conductivity of In2Se3@CNT (20%)/PEDOT:PSS interfacing with perovskite thereby increased the collection efficiency, charge extraction and hole mobilities of the device.

Photovoltaics literature survey (No. 181)

Photovoltaics literature survey (No. 181)

Nonfullerene Organic Solar Cells with 18.17% Efficiency Obtained Using a V2C/PEDOT:PSS Composite Hole-Transport Layer

More efficient promotion of charge collection and transport is an essential factor to achieve high efficiency of the devices; however, the matching of energy level between the PEDOT:PSS hole-transport layer (HTL) and indium tin oxide (ITO) is not perfect, which limits the efficiency of exciton utilization. Herein, the composite HTL of V2C/PEDOT:PSS is formed using two-dimensional (2D) conducting material V2C and PEDOT:PSS, which shows a lower work function (WF) and higher conductivity than the pure PEDOT:PSS films and shows advantages to improve the Ohmic contact between the active layer and electrode. The efficiency of the devices prepared with the V2C (0.075 mg/mL)/PEDOT:PSS composite HTL based on the nonfullerene PM6:BTP-eC9 system reaches 18.17%. The enhancement in performance can be ascribed to the interaction between the functional groups of V2C and PEDOT:PSS, as well as the increase in the overall hole-transport layer conductivity. The method proposed in this study to prepare this V2C/PEDOT:PSS composite HTL improves the efficiency of organic solar cells.

Building one-dimensional hole transport channels in cross-linked polymers to enable efficient deep blue QLED

Quantum dot light-emitting diodes (QLEDs) emerged as very competitive candidates for next generation display and lighting applications. Cross-linked hole transport materials (HTMs) permit the flourish of solution-processed QLEDs. Whereas, unbalanced charge injection and energy level mismatch happened to cross-linked HTMs severely suppress the efficiency of blue QLEDs, which limits the full-color display application. Here, discoid molecules with self-assembly behavior were firstly proposed to construct one-dimensional transport channels in cross-linked hole transport layer (HTL) to advance the carrier transport property of the target composite HTL (CHTL). Compared with CHTLs prepared from amorphous and disordered crystalline discoid molecules, the carrier mobility of CHTL (T5DP36: V-CBP) with one-dimensional transport channels was signally boosted by two orders of magnitude from 6.6 × 10−5 to 2.16 × 10−3 cm2 V−1 s−1. The relevant blue QLED was qualified with notably enhanced external quantum efficiency of 18.16 %, deep blue emission with Commission International de I’Eclaiiage of (0.14, 0.04) and extended T50 lifetime from 177 to 417 h under 100 cd m−2. This is at a cutting edge of deep blue light and eligible for high-end display applications.

Constructing Effective Hole Transport Channels in Cross-Linked Hole Transport Layer by Stacking Discotic Molecules for High Performance Deep Blue QLEDs.

The inadequate hole injection limits the efficiency and lifetime of the blue quantum dot light‐emitting diodes (QLEDs), which severely hampers their commercial applications. Here a new discotic molecule of 3,6,10,11‐tetrakis(pentyloxy)triphenylene‐2,7‐diyl bis(2,2‐dimethylpropanoate) (T5DP‐2,7) is introduced, in which the hole transport channels with superior hole mobility (2.6 × 10–2 cm2 V–1 s–1) is formed by stacking. The composite hole transport material (HTM) is prepared by blending T5DP‐2,7 with the cross‐linked 4,4′‐ bis(3‐vinyl‐9H‐carbazol‐9‐yl)‐1,1′biphenyl (CBP‐V) which shows the deep highest occupied molecular orbital energy level. The increased hole mobility of the target composite HTM from 10–4 to 10–3 cm2 V–1 s–1 as well as the stepwise energy levels facilitates the hole transport, which would be beneficial for more balanced carrier injection. This composite hole transport layer (HTL) has improved the deep‐blue‐emission performances of Commission International de I'Eclairage of (0.14, 0.04), luminance of 44080 cd m−2, and external quantum efficiency of 18.59%. Furthermore, when L0 is 100 cd m−2, the device lifetime T50 is extended from 139 to 502 h. The state‐of‐the‐art performance shows the successful promotion of the high‐efficiency for deep blue QLEDs, and indicates that the optimizing HTL by discotic molecule stacking can serve as an excellent alternative for the development of HTL in the future.

Effect of PVK mixed TAPC as hole transport layers on device performance of red quantum-dot light-emitting diodes

A series of red quantum-dot light-emitting diodes (QLEDs) are developed using poly(9-vinlycarbazole) (PVK) mixed 4,4′-Cyclohexylidenebis [N, N-bis(4-methylphenyl) benzenamine] (TAPC) as hole transport layer (HTL) by all-solution processing. The current density-voltage characteristics of carrier-only devices with emissive layer (EML) shows that the PVK: TAPC composite HTL exhibits the increase of current density at the same voltage with increasing the mixing concentration of TAPC. And the hole and electron currents are almost identical as the mixing concentration of TAPC is equal to 20%. The corresponding red QLED achieves the highest performance with a maximum luminance of 289 490 cd/m2, a maximum CE of 26.8 cd/A, a maximum EQE of 17.9% and a narrow full width at half-maximum (FWHM, 26 nm). The T50 lifetime is up to 65 min, which is more than 8 times longer than that of QLED with PVK as HTL at an initial luminance of 100 000 cd/m2. Furthermore, the efficiency roll-off is significantly reduced in the developed QLEDs. For instance, even at a very high brightness over 50 000 cd/m2, the QLEDs can still maintain a high CE of 26.6 cd/A and an EQE of 17.4%. The results show that the PVK: TAPC composite HTL builds energy level cascade to some degree and improve the hole transport capacity, leading to better charge carrier transfer balance. Consequently, the device performance is promoted.

Inkjet printing of composite hole transport layers and bulk heterojunction structure for organic solar cells

Thin solid films and inkjet printing technology have been investigated over a decade as being utilized for fabrication of an organic solar cell based on various nanomaterials such as carbon nanotube, graphene, fullerene, and macromolecules. Recent progress has shown its great potential to optimize the photovoltaic performances by means of inkjet printing. This paper presents the inkjet printing scheme to comprehensively fabricate the composite films and bulk heterojunction structures by varying solid concentration, droplet volume, and droplet spacing. As a result, it yielded a hole transport layer and a photoactive layer for the solar devices. The cell performances such as short-circuit current, open-circuit voltage, power conversion efficiency, series resistance, shunt resistance, fill factor, light dependence and stability were modelled, analyzed and evaluated in the study. A variety of composite films and materials fabricated by the scheme and nanomaterials could be applied in functional structures such as interfacial layers and electrodes for flexible solar cells in the future.

Interfacial Engineering of PTAA/Perovskites for Improved Crystallinity and Hole Extraction in Inverted Perovskite Solar Cells.

Inverted perovskite solar cells (PSCs) have gained rapid progress and increasing research interest in recent years. The poly (triarylamine) (PTAA) is the most frequently used semiconductor in the hole-transporting layer (HTL) in inverted PSCs for its favorable highest occupied molecular orbital energy level (-5.2 eV), excellent carrier mobility, and low-temperature solution processability. However, its intrinsic hydrophobic property hinders the growth of high-quality perovskite on the PTAA film, which is one of the main obstacles that limits the further development of inverted PSCs. Herein, a donor-acceptor-donor type organic molecule, 4,4',4″-(1-hexyl-1H-dithieno [3',2':3,4; 2″,3″:5,6] benzo[1,2-d] imidazole-2,5,8-triyl) tris (N,N-bis(4-methoxyphenyl) aniline) (denoted as M2), is employed to modify the surface of PTAA. The PTAA/M2 composite hole transport layer facilitates the growth of perovskite films due to ameliorated hydrophobic property of PTAA. PTAA/M2 also exhibits enhanced hole mobility and conductivity than pristine PTAA. With enhanced crystallinity and hole extraction ability, using PTAA/M2 instead of pure PTAA as HTL, the power-conversion efficiency of inverted PSC increases from 18.67% to 20.23%. Furthermore, its operational stability is also enhanced. Our methodology carves out a novel path for addressing the hydrophobic issue of PTAA and improving the efficiency and photostability of inverted PSCs.

Simultaneous improvement of efficiency and stability of inverted organic solar cellviacomposite hole transport layer

A novel composite hole transport layer is developed by combining 2PACz with MoO3. Inverted OSCs with the highest efficiency of 18.49% were achieved, which was much higher than that of the control device based on a MoO3HTL (17.46%).

Organic-inorganic hybrid hole transport layers with SnS doping boost the performance of perovskite solar cells

Perovskite solar cells (PSCs) have demonstrated excellent photovoltaic performance which currently rival the long-standing silicon solar cells’ efficiency. However, the relatively poor device operational stability of PSCs still limits their future commercialization. Binary sulfide is a category of materials with promising optoelectrical properties, which shows the potential to improve both the efficiency and stability of PSCs. Here we demonstrate that the inorganic tin monosulfide (SnS) can be an efficient dopant in 2,2′,7,7′-tetrakis(N,N-di-p-methoxy-phenylamine)-9,9′-spirobifluorene (spiro-OMeTAD) to form a composite hole transport layer (HTL) for PSCs. SnS nanoparticles (NPs) synthesized through a simple chemical precipitation method exhibit good crystallization and suitable band matching with the perovskites. The introduction of SnS NPs in Spiro-OMTAD HTLs enhanced charge extraction, reduced trap state density, and shallowed trap state energy level of the devices based on the composite HTLs. Therefore, the resulting solar cells employing SnS-doped spiro-OMeTAD HTLs delivered an improved stabilized power output efficiency of 21.75% as well as enhanced long-term stability and operational stability. Our results provide a simple method to modify the conventional spiro-OMeTAD and obtain PSCs with both high efficiency and good stability.

Efficient Planar Perovskite Solar Cells with Carbon Quantum Dot-Modified spiro-MeOTAD as a Composite Hole Transport Layer

In perovskite solar cells (PSCs), the hole-transport layer (HTL) plays an essential role in effective charge transport and extraction from the photoexcited perovskite, thus being significant for overall power conversion efficiency (PCE) and operational stability. So far, spiro-MeOTAD has been the most widely used HTL despite its inherent drawbacks, such as highly hygroscopic nature, poor conductivity, and mismatched energy-level alignment with the perovskite active layer. Here, a spiro-MeOTAD-based composite HTL modified by microwave method-synthesized carbon quantum dots (CQDs) was proposed and demonstrated as a promising HTL candidate for high-performance PSCs. The results demonstrated that the CQDs/spiro-MeOTAD composite HTL possesses several appealing characteristics for PSC applications, such as suitable energy levels for hole extraction, passivated interfacial trap states, and reduced recombination losses. Consequently, as compared to the control one using an unmodified spiro-MeOTAD HTL, (FAPbI3)0.95(MAPbBr3)0.05-based planar PSCs with composite HTL exhibit notably enhanced PCE and operational stability. Remarkably, an encouraging PCE of 20.41% was achieved for the champion device, and much improved operational stability was also demonstrated under continuous AM1.5 illumination with maximum power point (MPP) tracking conditions.

Polyaniline/Reduced Graphene Oxide Composites for Hole Transporting Layer of High-Performance Inverted Perovskite Solar Cells

We herein address the optoelectronic properties of polyaniline composite films with graphene oxide and reduced graphene oxide as a hole transport layer in inverted perovskite solar cells. The composite films exhibited enhanced electrical conductivity and suitable energy level matching with CH3NH3PbI3 for efficient hole extraction/transport than the pristine polyaniline film, which thus can deliver improved photovoltaic properties of device. The composite film-based devices exhibited maximum efficiency of 16.61%, which is enhanced by 21.6% from the device with the pristine polyaniline hole transport layer (efficiency = 13.66%). The reduced graphene oxide-based composite film also achieved improved long-term operative stability as compared to the pristine polyaniline-based device, demonstrating a great potential of reduced graphene oxide/polyaniline composite hole transport layer for high performance perovskite solar cells.

A Hybrid Hole Transport Layer for Perovskite-Based Solar Cells

This paper presents the effect of a composite poly(3,4-ethylenedioxythiophene) polystyrene sulfonate PEDOT:PSS and copper-doped nickel oxide (Cu:NiOx) hole transport layer (HTL) on the performance of perovskite solar cells (PSCs). Thin films of Cu:NiOx were spin-coated onto fluorine-doped tin oxide (FTO) glass substrates using a blend of nickel acetate tetrahydrate, 2-methoxyethanol and monoethanolamine (MEA) and copper acetate monohydrate. The prepared solution was stirred at 65 °C for 4 h and spin-coated onto the FTO substrates at 3000 rpm for 30 s in a nitrogen glovebox. The Cu:NiOx/FTO/glass structure was then annealed in air at 400 °C for 30 min. A mixture of PEDOT:PSS and isopropyl alcohol (IPA) (in 1:0.05 wt%) was spun onto the Cu:NiOx/FTO/glass substrate at 4000 rpm for 60 s. The multilayer structure was annealed at 130 °C for 15 min. Subsequently, the perovskite precursor (0.95 M) of methylammonium iodide (MAI) to lead acetate trihydrate (Pb(OAc)2·3H2O) was spin-coated at 4000 rpm for 200 s and thermally annealed at 80 °C for 12 min. The inverted planar perovskite solar cells were then fabricated by the deposition of a photoactive layer (CH3NH3PbI3), [6,6]-phenyl C61-butyric acid methyl ester (PCBM), and a Ag electrode. The mechanical behavior of the device during the fabrication of the Cu:NiOx HTL was modeled with finite element simulations using Abaqus/Complete Abaqus Environment CAE. The results show that incorporating Cu:NiOx into the PSC device improves its density–voltage (J–V) behavior, giving an enhanced photoconversion efficiency (PCE) of ~12.8% from ~9.8% and ~11.5% when PEDOT:PSS-only and Cu:NiOx-only are fabricated, respectively. The short circuit current density Jsc for the 0.1 M Cu:NiOx and 0.2 M Cu:NiOx-based devices increased by 18% and 9%, respectively, due to the increase in the electrical conductivity of the Cu:NiOx which provides room for more charges to be extracted out of the absorber layer. The increases in the PCEs were due to the copper-doped nickel oxide blend with the PEDOT:PSS which enhanced the exciton density and charge transport efficiency leading to higher electrical conductivity. The results indicate that the devices with the copper-doped nickel oxide hole transport layer (HTL) are slower to degrade compared with the PEDOT:PSS-only-based HTL. The finite element analyses show that the Cu:NiOx layer would not extensively deform the device, leading to improved stability and enhanced performance. The implications of the results are discussed for the design of low-temperature solution-processed PSCs with copper-doped nickel oxide composite HTLs.

Enhanced organic photovoltaic performance through promoting crystallinity of photoactive layer and conductivity of hole-transporting layer by V2O5 doped PEDOT:PSS hole-transporting layers

The fill factor (FF) as an important photovoltaic parameter is related to the property of transport layers and active layers for organic solar cells (OSCs). Herein, we propose a simple method to improve FF by using inorganic-organic composite hole transport layer (HTL) in OSCs. Through incorporating inorganic metal oxide, vanadium pentoxide (V2O5) nanoparticles into PEDOT:PSS, the morphology and conductivity of the composite HTL are improved, due to V2O5 nanoparticles can fill the pinholes in PEDOT:PSS and expose more PEDOT chains to the surface core–shell structure. The PTB7-Th:PC71BM-based OSCs with different HTLs were prepared. The power conversion efficiency and FF of the OSCs for the composite HTL can be greatly improved compared with the traditional HTL, which can reach up to 9.44% and 70.14%, respectively. The results of water contact angle and grazing incidence wide-angle X-ray scattering show that the hydrophobicity of the composite HTL is improved, which can not only improve the physical contact but also greatly affect the subsequent active layer formation, thus increasing the crystallinity of PTB7-Th:PC71BM. These results demonstrate that V2O5:PEDOT:PSS has good application prospects as a HTL to realize high-efficient OSCs.