Solution-processed Hole Transport Layer Research Articles

Molecular Orientation Regulation of Hole Transport Semicrystalline-Polymer Enables High-Performance Carbon-Electrode Perovskite Solar Cells.

Carbon-based perovskite solar cells (PSCs) coupled with solution-processed hole transport layers (HTLs) have shown potential owing to their combination of low cost and high performance. However, the commonly used poly(3-hexylthiophene) (P3HT) semicrystalline-polymer HTL dominantly shows edge-on molecular orientation, in which the alkyl side chains directly contact the perovskite layer, resulting in an electronically poor contact at the perovskite/P3HT interface. The study adopts a synergetic strategy comprising of additive and solvent engineering to transfer the edge-on molecular orientation of P3HT HTL into 3D molecular orientation. The target P3HT HTL possesses improved charge transport as well as enhanced moisture-repelling capability. Moreover, energy level alignment between target P3HT HTL and perovskite layer is realized. As a result, the champion devices with small (0.04 cm2) and larger areas (1 cm2) deliver notable efficiencies of 20.55% and 18.32%, respectively, which are among the highest efficiency of carbon-electrode PSCs.

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.

Poly(3,4-ethylenedioxythiophene)/poly(bis(4-phenoxysulfonic acid)phosphazene) conductive composites: an alternative interfacial layer to PEDOT : PSS

An alternative solution processable hole transport layer based on PEDOT have been developed and compared with the poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT : PSS).

Surface photovoltage predicts open circuit voltage in GaP/PEDOT:PSS and GaP/CuSCN heterojunction solar cells

Surface photovoltage spectroscopy measures the contribution of solution-processed hole transport layers to the photovoltage of GaP solar cells.

Enhancing performance of inverted quantum-dot light-emitting diodes based on a solution-processed hole transport layer via ligand treatment

The performance of inverted quantum-dot light-emitting diodes (QLEDs) based on solution-processed hole transport layers (HTLs) has been limited by the solvent-induced damage to the quantum dot (QD) layer during the spin-coating of the HTL. The lack of compatibility between the HTL's solvent and the QD layer results in an uneven surface, which negatively impacts the overall device performance. In this work, we develop a novel method to solve this problem by modifying the QD film with 1,8-diaminooctane to improve the resistance of the QD layer for the HTL’s solvent. The uniform QD layer leads the inverted red QLED device to achieve a low turn-on voltage of 1.8 V, a high maximum luminance of 105 500 cd/m2, and a remarkable maximum external quantum efficiency of 13.34%. This approach releases the considerable potential of HTL materials selection and offers a promising avenue for the development of high-performance inverted QLEDs.

MWCNT/Cr2O3 nanocomposite as a solution-processed hole transport layer for cost-effective perovskite solar cells with long-term stability

Utilization of systems that can bypass costly materials and methods and have long-term stability is critical for the commercialization of perovskite solar cells (PSCs). Since hole transport materials (HTM) are the major costly layers in PSCs, finding a suitable replacement would be advantageous. Two types of mesoporous PSCs were fabricated using the solution-processed Cr2O3 in pure and composite form with multi-walled carbon nanotube (MWCNT/Cr2O3) as dopant-free, hydrophobic HTM layers. Incorporation of the Cr2O3 into MWCNT rendered improved morphological characteristics and better energy level alignment, facilitating the extraction of holes. Furthermore, such a modification suppresses the hysteresis and interfacial recombination of charges, resulting in a device with long-term stability and the PCE boosted from 12.22 % (bare Cr2O3) to 16.29 % (MWCNT/Cr2O3 nanocomposite). The reason for the increased efficiency of the composite layer than bare Cr2O3 is the decrease of interfacial recombination of charges proved by various electrochemical analysis. The lifetime and processes of transfer and recombination of charges in the interfacial contact as well as hole mobility were explored through various electrochemical techniques. As a result, this work not only demonstrates the potential application of MWCNT/Cr2O3 as an HTM layer for realizing efficient PSC, but also provides a fundamental insight for achieving cost-effective photovoltaic devices with acceptable efficiencies and remarkable stability with just a 0.32 % drop of PCE after 50 days in relative humidity ∼ 40 % under one-sun illumination.

Thermally Stable Perovskite Solar Cells by All-Vacuum Deposition.

Vacuum deposition is a solvent-free method suitable for growing thin films of metal halide perovskite (MHP) semiconductors. However, most reports of high-efficiency solar cells based on such vacuum-deposited MHP films incorporate solution-processed hole transport layers (HTLs), thereby complicating prospects of industrial upscaling and potentially affecting the overall device stability. In this work, we investigate organometallic copper phthalocyanine (CuPc) and zinc phthalocyanine (ZnPc) as alternative, low-cost, and durable HTLs in all-vacuum-deposited solvent-free formamidinium-cesium lead triodide [CH(NH2)2]0.83Cs0.17PbI3 (FACsPbI3) perovskite solar cells. We elucidate that the CuPc HTL, when employed in an "inverted" p-i-n solar cell configuration, attains a solar-to-electrical power conversion efficiency of up to 13.9%. Importantly, unencapsulated devices as large as 1 cm2 exhibited excellent long-term stability, demonstrating no observable degradation in efficiency after more than 5000 h in storage and 3700 h under 85 °C thermal stressing in N2 atmosphere.

Topological Design of Highly Anisotropic Aligned Hole Transporting Molecular Bottlebrushes for Solution-Processed OLEDs.

Polyvinyl polymers bearing pendant hole transport functionalities have been extensively explored for solution-processed hole transport layer (HTL) technologies, yet there are only rare examples of high anisotropic packing of the HT moieties of these polymers into substrate-parallel orientations within HTL films. For small molecules, substrate-parallel alignment of HT moieties is a well-established approach to improve overall device performance. To address the longstanding challenge of extension from vapor-deposited small molecules to solution-processable polymer systems, a fundamental chemistry tactic is reported here, involving the positioning of HT side chains within macromolecular frameworks by the construction of HT polymers having bottlebrush topologies. Applying state-of-the-art polymer synthetic techniques, various functional subunits, including triphenylamine (TPA) for hole transport and adhesion to the substrate, and perfluoro alkyl-substituted benzyloxy styrene for migration to the air interface, were organized with exquisite control over the composition and placement throughout the bottlebrush topology. Upon assembling the HT bottlebrush (HTB) polymers into monolayered HTL films on various substrates through spin-casting and thermal annealing, the backbones of HTBs were vertically aligned while the grafts with pendant TPAs were extended parallel to the substrate. The overall design realized high TPA π-stacking along the out-of-plane direction of the substrate in the HTLs, which doubled the efficiency of organic light-emitting diodes compared with linear poly(vinyl triphenylamine)s.

Graphene oxide-molybdenum oxide composite with improved hole transport in bulk heterojunction solar cells

Solution processed hole transport layer based on graphene oxide (GO) and molybdenum oxide (MoO3) composite in bulk heterojunction organic solar cell (OSC) devices offer low cost, improved performance compared to conventional organic solar cells. Here, we have made a study comparing the power conversion efficiency (PCE) of this composite to the pristine GO and MoO3 as a hole transport layer in the organic photovoltaics. The devices with the composite shows optimized performance with PCE of ∼ 5.1%, while the pristine GO and MoO3 display 1.59% and 2.5%, respectively. These differences are attributed to the lower short circuit current (Jsc) and thereby lower fill factor (FF) with respect to the GO and MoO3. Nevertheless, the composite based devices exhibits improved optical absorption and photoluminescence quenching as compared to pristine interface layer. This study intends to highlight efficient modulation of the interface barrier of hole transport layer which allow us to give faster transport and extraction of the charge carrier efficiently at the electrodes.

Copper Bromide as an Efficient Solution-Processable Hole Transport Layer for Organic Solar Cells: Effect of Solvents.

In this work, we report copper bromide (CuBr) as an efficient, inexpensive, and solution-processable hole transport layer (HTL) for organic solar cells (OSCs) for the first time. To examine the effectiveness of the material in general, three different solvents such as acetonitrile (MeCN), dimethyl sulfoxide (DMSO), and dimethylformamide (DMF) are used for solution-processing thin-film deposition of CuBr. CuBr thin films deposited from different solvents show high transparency and no significant difference has been observed in absorption in the visible and near-IR range, whereas a slight difference has been found in the near-UV range by changing the solvents. Furthermore, two most studied combinations of the active layer such as PTB7/PC71BM and PCDTBT:/PC71BM are used for device fabrication with geometry of ITO/CuBr(HTL) active layer/Al. By using CuBr as a HTL in OSCs, the power conversion efficiencies (PCEs) have been achieved to up to 5.16 and 4.72% with PTB7/PC71BM and PCDTBT/PC71BM active layers, respectively. The CuBr film from DMF solvent shows highest PCE as compared to films deposited from DMSO and MeCN solvents. Different solvents used for HTL deposition have a major effect on the fill factor (FF), while very little difference on open circuit voltage (Voc) and short circuit current (Jsc) has been observed. It may be mentioned here that a small difference of device parameters (PCE, FF, Jsc, and Voc) has been observed in the devices using the HTL deposited from DMF and DMSO solvents, whereas a significant difference of the device parameters has been found in devices using the HTL from MeCN solvent.

Improved performance of organic solar cells with solution processed hole transport layer

This work is based on Cobalt Oxide as solution processed, inexpensive and effective hole transport layer (HTL) for efficient organic photovoltaic applications (OPVs). In Organic solar cell (OSC) devices ITO coated glass substrate used as a transparent anode electrode for light incident, HTL material Co3O4 dissolve in DMF solvent deposited on anode electrode, after that active layer material (donor/acceptor) deposited on to HTL and finally Al were deposited by thermal evaporation used as cathode electrode. These devices were fabricated with PCDTBT well known low band gap donor material in OSCs and blended with PC71BM as an acceptor material using simplest device structure ITO/Co3O4/active layer/Al at ambient conditions. The power conversion efficiencies (PCEs) based on Co3O4 and PEDOT:PSS have been achieved to up to 3.21% and 1.47% with PCDTBT respectively. In this study we reported that the devices fabricated with Co3O4 showed better performance as compare to the devices fabricated with well known and most studied solution processed HTL material PEDOT:PSS under identical environmental conditions. The surface morphology of the HTL film was characterized by (AFM). Lastly, we have provided Co3O4 as an efficient hole transport material HTL for solution processed organic photovoltaic applications.

Solution processed hole transport layer towards efficient and cost effective organic solar cells

In this work, we report Copper Sulfide (CuS) as a solution processed, inexpensive and effective hole transport layer (HTL) for efficient and low cost organic solar cells. These devices were fabricated using two most studied low band gap donor materials PTB7 and PCDTBT blended with PC71BM as an acceptor material. We have used a simplest device architect such as ITO/CuS/active layer/Al at ambient conditions. The power conversion efficiencies (PCEs) of these devices have been achieved to up to 4.32% and1.76 % for PTB7 and PCDTBT based devices respectively. Finally, we have provided a further example of solution processable CuS as an effective HTL for solution processable organic photovoltaic applications.

Copper (I) Selenocyanate (CuSeCN) as a Novel Hole‐Transport Layer for Transistors, Organic Solar Cells, and Light‐Emitting Diodes

AbstractThe synthesis and characterization of copper (I) selenocyanate (CuSeCN) and its application as a solution‐processable hole‐transport layer (HTL) material in transistors, organic light‐emitting diodes, and solar cells are reported. Density‐functional theory calculations combined with X‐ray photoelectron spectroscopy are used to elucidate the electronic band structure, density of states, and microstructure of CuSeCN. Solution‐processed layers are found to be nanocrystalline and optically transparent (>94%), due to the large bandgap of ≥3.1 eV, with a valence band maximum located at −5.1 eV. Hole‐transport analysis performed using field‐effect measurements confirms the p‐type character of CuSeCN yielding a hole mobility of 0.002 cm2 V−1 s−1. When CuSeCN is incorporated as the HTL material in organic light‐emitting diodes and organic solar cells, the resulting devices exhibit comparable or improved performance to control devices based on commercially available poly(3,4‐ethylenedioxythiophene):polystyrene sulfonate as the HTL. This is the first report on the semiconducting character of CuSeCN and it highlights the tremendous potential for further developments in the area of metal pseudohalides.

Diamine-cored tetrastilbene compounds as solution-processable hole transport materials for stable organic light emitting diodes

A series of diamine-cored tetrastilbene (DTS) derivatives bearing various aliphatic and aromatic substituents was designed and synthesized for use as solution-processed hole transport layers (HTLs) in organic light emitting diodes (OLEDs). The chemical structures of the DTS derivatives were strategically designed to increase solubility in organic solvents as well as to avoid self-crystallization, and thus ensure a stable morphology under Joule heating while maintaining efficient hole transport capabilities. The five DTS derivatives, composed of different conjugation structures, yielded reasonably good hole transport behavior with a marginal charge carrier mobility of ∼10−5 cm2V−1s−1, which is similar to that of vacuum-deposited N,N′-bis(1-naphthyl)-N,N′-diphenyl-1,1′-biphenyl-4,4′-diamine (NPB). Due to the high glass transition temperatures of the DTS derivatives, this satisfactory charge transport behavior and smooth surface morphology were conserved up to 180 °C. Green OLEDs were prepared using tris-(8-hydroxyquinoline) aluminum (Alq3):C545T as the emission layer, and the OLED performances of the solution-processed DTS HTLs and the vacuum-deposited NPB HTL were compared. A high luminance efficiency of 11.5 cd A−1 was obtained for one solution-processed DTS HTL, which exceeds that of the NPB HTL (10.01 cd A−1). Furthermore, the DTS HTLs enabled a stable OLED operation, with double the accelerated half-life of the NPB-based device.

P‐240: Late‐News Poster: Inverted Hybrid Quantum Dot LED with Blue Polymer as Both Hole Transporting Layer and Emission Layer

A blue polymer poly (dibenzothiophene‐S,S‐dioxide‐co‐9,9‐dioctyl‐2,7‐fluorene) (PFSO) was introduced as the solution processed hole transport layer (HTL) in an inverted red quantum dots LED (QLED). The device exhibits a turn‐on voltage of 2.0 V, a peak current efficiency of 12.0 cd/A, and a maximum brightness of 9700 cd/m2. The blue polymer functions as both HTL and emission layer (EML) by inkjet printing red QDs to expose the blue polymer to the electron transporting layer (ETL). Though the device has decent performance with 2.2 V turn‐on voltage, and 7.7 lm/W power efficiency, the device color is purple because of no green emission. By adding green QDs to the hybrid device, white LED will be realized.

Efficient and Stable Vacuum-Free-Processed Perovskite Solar Cells Enabled by a Robust Solution-Processed Hole Transport Layer.

Here, efficient and stable vacuum-free processed perovskite solar cells (PSCs) are demonstrated by employing solutionprocessed molybdenum tris-[1-(trifluoroethanoyl)-2-(trifluoromethyl)ethane-1,2-dithiolene] (Mo(tfd-COCF3 )3 )-doped poly(3,4-ethylenedioxythiophene) (PEDOT) film as hole transport layer (HTL). Our results indicate that the incorporation of Mo(tfd-COCF3 )3 dopant can induce p-doping through charge transfer from the highest occupied molecular orbital (HOMO) level of the PEDOT host to the electron affinity of Mo(tfd-COCF3 )3 , leading to an increase in conductivity by more than three orders of magnitude. With this newly developed p-doped film as HTL in planar heterojunction PSCs, a high power conversion efficiency (PCE) up to 18.47 % can be achieved, which exceeds that of the device with commonly used HTL 2,2',7,7'-tetrakis(N,N-di-p-methoxyphenyl-amine)9,9'-spirobifluorene (spiro-OMeTAD). Taking the advantage of the high conductivity of this doped film, a prominent PCE as high as 15.58 % is also demonstrated even when a large HTL thickness of 220 nm is used. Importantly, the high quality film of this HTL is capable of acting as an effective passivation layer to keep the underlying perovskite layer intact during solution-processed Ag-nanoparticles layer deposition. The resulting vacuum-free PSCs deliver an impressive PCE of 14.81 %, which represents the highest performance ever reported for vacuum-free PSCs. Furthermore, the resulting devices show good ambient stability without encapsulation.

Bulk Heterojunction Organic Solar Cells with Graphene Oxide Hole Transport Layer: Effect of Varied Concentration on Photovoltaic Performance

We report solution processable hole transport layer (HTL) for bulk heterojunction organic solar cells (BHJ OSCs) based on varied concentration of graphene oxide (GO) in aqueous suspension. The effects of varied concentration of GO at 1, 2, and 4 mg/mL on the morphological, optical, electrical, and photovoltaic properties of the OSCs have been studied. Device with the lowest concentration and least thickness of GO showed most optimized performance with a power conversion efficiency (PCE) of 2.73%, as compared to the higher concentrations, where the PCE reduced to 0.67 and 0.22% for the devices with HTL of 2 and 4 mg/mL, respectively. The remarkable reduction in the device performance at higher concentrations is mainly attributed to a drastic decrease in the short circuit current that reduced from 8.14 mA/cm2 to 2.90 and 1.10 mA/cm2 at 2 and 4 mg/mL, respectively. Similarly, the increased series resistance (Rs) from 6.89 Ω/cm2 to 9.54 and 11.51 Ω/cm2 has also reduced the device performance. Optical transmit...

Poly(Styrene Sulfonate) Free Poly(3,4-Ethylenedioxythiophene) as a Robust and Solution-Processable Hole Transport Layer for Organic Solar Cells

We first time report poly(styrene sulfonate) (PSS) free poly(3,4-ethylenedioxythiophene) (PEDOT) as a novel solution-processable hole transport layer (HTL) for organic solar cells. The transparent and conducting PEDOT thin film was obtained by solid state polymerization (SSP) of 2,5-dibromo-3,4-ethylenedioxythiophene (DBEDOT) on ITO coated glass substrate (by heating of the monomer at 60 °C for overnight). The thicknesses of the obtained thin films were optimized by using different concentrations of DBEDOT in chlorobenzene during spin coating. Two different combinations of active layers such as poly(3-hexylthiophene):phenyl-C61-butyric acid methyl ester (P3HT:PC61BM) and poly[N-9′-heptadecanyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole)]:phenyl-C71-butyric acid methyl ester (PCDTBT:PC71BM) were used for device fabrication. Power conversion efficiencies were achieved up to 0.71 % and 1.70 % in a simple geometry of ITO/ssp-PEDOT/active layer/Al under ambient conditions. The potential importances of the ssp-PEDOT as an HTL are robust, stable, PSS free and solution-processable for organic solar cells.

Copper thiocyanate (CuSCN): an efficient solution-processable hole transporting layer in organic solar cells

Here, we report copper(i)thiocyanate (CuSCN) as an efficient and solution-processable hole transport layer (HTL) in bulk heterojunction solar cells.

33.2: Solution Processed Hole Injection and Hole Transport Layers: Design Features for OLED Manufacturing

AbstractWe present recent developments of our core technologies targeted towards solution based OLED device manufacturing including non‐aqueous (NQ) hole injection layer and solution processed hole transport layer. We demonstrate low voltage, and long lifetime devices with non‐aqueous hole injection layer. Also, comparable performance with our intractable solution processed HTL versus NPB vapor HTL has been demonstrated in vapor WOLED devices in combination with our NQ hole injection layer technology.