Doped Hole Transport Layer Research Articles

Solution-Processed Thick Hole-Transport Layer for Reliable Quantum-Dot Light-Emitting Diodes Based on an Alternatingly Doped Structure.

The operating lifetime of quantum-dot light-emitting diodes (QLED) is a bottleneck for commercial display applications. To enhance the operational stability of QLEDs, we developed a robust solution-processed highly conductive hole-transport-layer (HTL) structure, which enables a thick HTL structure to mitigate the electric field. An alternating doping strategy, which involves multiple alternating stacks of N4,N4'-di(naphthalen-1-yl)-N4,N4'-bis(4-vinylphenyl)biphenyl-4,4'-diamine and phosphomolybdic acid layers, could provide significantly improved conductivity; more specifically, the 90 nm-thick alternatingly doped HTL exhibited higher conductivity than the 45 nm-thick undoped HTL. Therefore, when applied to a QLED, the increase in the thickness of the alternatingly doped HTL increased device reliability. As a result, the lifetime of the QLED with a thick, alternatingly doped HTL was 48-fold higher than that of the QLED with a thin undoped HTL. This alternating doping strategy provides a new paradigm for increasing the stability of solution-based optoelectronic devices in addition to QLEDs.

Chemical polishing strategies to improve flexible perovskite solar cells based on dopant-free hole transport layers

For n-i-p typed flexible perovskite solar cells (fPSCs), the doped hole transport layer significantly impacts the devices' long-term stability. Using dopant-free organic hole transport materials (d-HTMs) is promising for stable fPSCs. However, the low conductivity of d-HTMs limited their thickness, making them sensitive to the surface morphology of the perovskite film's upper surface. Here, we report a chemical polishing strategy using 1-hexyl-3-methylimidazolium acetate (HMIM∙Ac) as the polishing reagent to enhance the upper surface of the perovskite film, which could form a smooth and flat surface. Meanwhile, the treatment can reduce surface defects and smaller grains on top of the surface. Then, we deposite an ultra-thin dopant-free PM6 layer, a typical hole transport layer, on top of the polished perovskite film. The PM6 layer shows an improved face-on orientation and then carrier mobility. Moreover, suppressed non-radiative recombination at the perovskite/PM6 interface is also observed, translating into a higher open-circuit voltage and fill factor of the fPSCs. As a result, a champion power conversion efficiency (PCE) of 17.76 ​%, with an open-circuit voltage of 1.025 ​V and fill factor of 78.2 ​%, is obtained, which is one of the highest PCEs among the reported fPSCs based on d-HTMs. Our strategy demonstrates a facile but effective way of developing high-efficiency and stable fPSCs for future applications.

Is Doping of Spiro-OMeTAD a Requirement for Efficient and Stable Perovskite Indoor Photovoltaics?

Lead halide perovskite (LHP) photovoltaics deliver high voltages even under low-light illumination intensities, thus emerging as a promising indoor photovoltaic (IPV) technology. The doping of the 2,2′,7,7′-tetrakis( N , N -di-p-methoxyphenylamino)-9,9′-spirobifluorene (Spiro-OMeTAD) hole-transport layer (HTL) is the most widely adopted strategy for high-performance LHP-based solar cells. Yet, the importance of Spiro-OMeTAD doping is unclear in the context of indoor photovoltaics. In this report, we examine the role of the traditional Spiro-OMeTAD dopants on the performance of LHP-based IPVs. The diminished influence of the series resistance under indoor lighting leads to an improved fill factor of IPV devices even in the absence of the dopants. The pristine (dopant-free) Spiro-OMeTAD HTL ensures a power conversion efficiency (PCE) as high as 25.6% at 1,000 lux, comparable to that of 29.7% in the presence of the dopants, and an open-circuit voltage of ≈0.65 V even at 50 lux. The undoped Spiro-OMeTAD-containing devices exhibit a ≈25% gain in their PCE under long-term and continuous white light illumination at the maximum power point, thus leading to the PCE values on par or higher than those of employing doped Spiro-OMeTAD. Furthermore, the current–voltage hysteresis behavior of the undoped Spiro-OMeTAD-containing devices remains unchanged in the 100 to 1,000 lux light-intensity range, unlike the case of doped Spiro-OMeTAD HTL. Our findings suggest that the dopants in Spiro-OMeTAD HTL are not required to achieve efficient, stable, and reliable IPV performance, and the optimization of the various device constituents for outdoor solar cell applications may not necessarily lead to the best performance for indoor photovoltaics.

Lithium Salt‐Doped Organic Conjugated Hole Transport Layer for High‐Performance PbS Quantum Dot Solar Cells

The electrical properties of hole transport layers (HTL) are critical factors for the high performance of lead sulfide quantum dot solar cells (PbS CQDSCs). Herein, the impacts of doping the organic HTL PTB7‐Th with lithium bis(trifluoromethanesulfonimide) (LiTSFI) on the performance of quantum dot solar cells are explored and a notable enhancement in the fill factor is observed. A series of analytical characterizations of the doped HTLs are performed and it is found that doping with LiTFSI significantly deepens the Fermi level of the HTL, thereby improving the charge separation ability within the devices. Additionally, the conductivity of doped HTL is also improved. By optimizing the doping conditions, the doped device achieves a maximum power conversion efficiency of 12.68%. This doping strategy of organic HTL promotes the development of lead sulfide quantum dot solar cell techniques.

Hybrid silver/silver-oxide nanoparticles doped hole transport layer for efficient photon harvesting in organic solar cells

Hybrid silver/silver-oxide nanoparticles doped hole transport layer for efficient photon harvesting in organic solar cells

Enhanced Performance of Perovskite Solar Cells Based on Zn2+ Doped Nico2o4 Nws Hole Transport Layers

Enhanced Performance of Perovskite Solar Cells Based on Zn2+ Doped Nico2o4 Nws Hole Transport Layers

Cross-Linking of Doped Organic Semiconductor Interlayers for Organic Solar Cells: Potential and Challenges

Solution-processable interlayers are important building blocks for the commercialization of organic electronic devices such as organic solar cells. Here, the potential of cross-linking to provide an insoluble, stable, and versatile charge transport layer based on soluble organic semiconductors is studied. For this purpose, a photoreactive tris-azide cross-linker is synthesized. The capability of the small molecular cross-linker is illustrated by applying it to a p-doped polymer used as a hole transport layer in organic solar cells. High cross-linking efficiency and excellent charge extraction properties of the cross-linked doped hole transport layer are demonstrated. However, at high doping levels in the interlayer, the solar cell efficiency is found to deteriorate. Based on charge extraction measurements and numerical device simulations, it is shown that this is due to diffusion of dopants into the active layer of the solar cell. Thus, in the development of future cross-linker materials, care must be taken to ensure that they immobilize not only the host but also the dopants.

One‐Source Strategy Boosting Dopant‐Free Hole Transporting Layers for Highly Efficient and Stable CsPbI2Br Perovskite Solar Cells

AbstractAll‐inorganic perovskites have emerged as promising photovoltaic materials due to their superior thermal stability compared to their organic–inorganic hybrid counterparts. However, the inferior film quality and doped hole transport layer (HTL) have a strong tendency to degrade the perovskite under high temperatures or harsh operating conditions. To solve these problems, a one‐source strategy using the same polymer donor material (PDM) to simultaneously dope CsPbI2Br perovskite films via antisolvent engineering and fabricating the HTL is proposed. The doping assists perovskite film growth and forms a top–down gradient distribution, generating CsPbI2Br with enlarged grain size and reduced defect density. The PDM as the HTL suppresses the energy barrier and forms favorable electrical contacts for hole extraction, and assemble into a fingerprint‐like morphology that improves the conductivity, facilitating the creation of a dopant‐free HTL. Based on this one‐source strategy using PBDB‐T as PDM, the CsPbI2Br perovskite solar cell with a dopant‐free HTL achieves a power conversion efficiency (PCE) of 16.40%, which is one of the highest PCEs reported among all‐inorganic CsPbI2Br pero‐SCs with a dopant‐free HTL. Importantly, the devices exhibit the highest thermal stability at 85 °C and operational stability under continuous illumination even with Ag as the top electrode and present good universality.

Charge carrier performance of phosphazene-based ionic liquids doped hole transport layer in organic light-emitting diodes

The enhancement of hole injection layers is strongly important issue for obtaining high-efficient and low-driving-voltage Organic Light-Emitting Devices (OLEDs). In this paper, we presented a comprehensive electroluminescence (EL) study of phosphazene-based ionic liquids (PzILs) used as a hole transport layer in solution-processed OLEDs. Charge transfer properties of PzILs were investigated by doping in poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) at different ratios (0.1, 0.2, 0.5, 1.0, 2.0). Previously synthesized four types of PzILs (namely PzIL1, PzIL2, PzIL3, and PzIL4) were prepared in de-ionized water with 10 mg/ml concentration, mixed with PEDOT:PSS and examined for their charge transport characteristics on OLED device performance due to their ionic nature. The device with PzIL1 exhibited the best performance with luminance 4185 cd/m2 compared to other devices with and without PzILs. Further, Density Functional Theory (DFT) calculations and admittance spectroscopic analysis of OLEDs based on four types of PzILs were studied profoundly. Admittance spectroscopy has been used for revealing the carrier transport properties, mobility and the equivalent circuit modeling of the devices. Four types of PzILs OLEDs represented typical p-type transporting characteristics with moderate mobility up to 1.93 cm2/V.s.

Primary color generation from white organic light-emitting diodes using a cavity control layer for AR/VR applications

Abstract In this paper, we report primary color generation method from white top-emission organic light emitting diodes (WTEOLEDs) by applying cavity control layer (CCL) for achieving high resolution display. In order to realize primary colors, we applied high efficiency two-stack WTEOLED structure with solution processed indium zinc oxide CCL. Using optically designed two-stack WTEOLED with CCL, we fabricated red, green, and blue TEOLEDs with current efficiency of 34.9, 79.5, and 3.4 cd/A, respectively. However, there is an issue of intense blue emission in the red color device due to its cavity condition. To suppress this blue emission, silver nanoparticles doped electron transfer layer and rubrene doped hole transport layer methods were successively used due to their high absorption in the blue region. By applying these two methods together, top-emission red device showed 80% reduction in blue color intensity.

Fabrication and TCAD validation of ambient air-processed ZnO NRs/CH3NH3PbI3/spiro-OMeTAD solar cells

This paper reports the fabrication, characterization and simulation of hybrid perovskite solar cells (PSCs) in ambient condition. The proposed PSC structures use a CH 3 NH 3 PbI 3 hybrid perovskite based active layer sandwiched between a ZnO nanorods (NRs) electron transport layer (ETL) and a spiro-OMeTAD (undoped and doped) hole transport layer (HTL). The ZnO NRs are grown using low-cost solvothermal process at relatively low temperature. The performance of fabricated PSCs are analyzed for both the undoped and doped (with TBP and LiTFSI) spiro-OMeTAD based HTLs. All the solar parameters namely, short circuit current density ( J SC ), open circuit voltage ( V OC ), fill factor ( FF ), power conversion efficiency ( PCE ) and external quantum efficiency ( EQE ) are calculated from experimentally measured current density versus voltage ( J-V ) and wavelength transient characteristics in ambient condition. The maximum PCE of 10.18% is obtained for the doped HTL whereas 9.51% for undoped HTL. The improved performance due to HTL doping is attributed to the enhanced charge transportation of the HTL. The experimental results obtained from the fabricated PSCs are also compared with the SetFos™ TCAD simulation data using drift-diffusion model. The simulated results are observed to be well matched to the experimental data. • PSCs with 10.18% PCE fabricated under ambient-air atmosphere. • PSCs for undoped and doped HTL validated using SetFos™ TCAD simulation. • ZnO NRs grown by solvothermal process upon ZnO QDs sheet layer coated on FTO.

Efficiency Enhancement of Perovskite CsPbBr3 Quantum Dot Light-emitting Diodes by Doped Hole Transport Layer

Balanced charge injection is essential to high-performance Perovskite CsPbBr3 quantum dot-based light-emitting diodes (QLEDs). However, low mobility of hole-transport materials (HTMs) severely restrict improving performance of QLEDs. Herein, we provide a novel HTMs to improve the highest occupied molecular orbital (HOMO) energy level structure and carrier mobility by doping poly (9-vinlycarbazole) (PVK) and poly [N, N’-bis(4-butylphenyl)-N, N’-bis(phenyl) benzi-dine] (poly-TPD). We also introduce poly (methyl methacrylate) (PMMA) as electron block layer to further achieve charge injection balance. Finally, an enhanced external quantum efficiency (EQE) of 0.53% and 414.83 cd/m2 was obtained. Compared with the untreated QLED, this result has been 8-fold enhanced, provides a new approach to attain better performance.

Editors' Choice—Stability of Unstable Perovskites: Recent Strategies for Making Stable Perovskite Solar Cells

Perovskite solar cells (PSCs) are now crossing the certified 23.2% power conversion efficiency (PCE), however, the stability of organic-lead halide perovskites, cost of additives doped hole transport layer (HTL) and upscaling from lab-scale to industrial scale without hampering its efficiency are challenging tasks for its commercial application. These problems could be tackled via different aspects which includes the synthesis of promising electron transport layers (ETLs) and HTLs, synthesis of mixed perovskites via combination of 3D and stable 2D perovskite, replacement of poor-stable methylammonium (MA) cation with MA free perovskite and capping inorganic materials will be the best choice toward highly efficient air-thermal-stable perovskite solar cells (PSCs). This perspective focuses on the current strategies in PSCs for making the stable PSCs via low-cost, easily processed components and shared our views toward commercialization.

Enhanced efficiency and high temperature stability of hybrid quantum dot light-emitting diodes using molybdenum oxide doped hole transport layer.

High power efficiency (PE) and stability of quantum dot (QD) light-emitting diodes (QLEDs) are important factors for practical use in various displays. However, hybrid QLEDs consisting of an organic hole transport layer (HTL) and an inorganic electron transport layer (ETL) sometimes have poor stability due to the low thermal stability of the organic HTL. To solve the problem, here, we report enhanced efficiency, lifetime, and temperature stability in inverted and hybrid structured QLEDs by adopting a MoO3-doped HTL. Also, to improve the electron–hole charge carrier balance, a thin insulating interlayer was used between QDs and the ETL. As a result, the QLED with the p-doped HTL exhibited the increased PE by ∼28% and longer lifetime compared to the pristine QLEDs. In addition, the QLED showed stable operation at the high temperature up to 400 K, whereas the control device failed to operate at 375 K. We systematically investigated the effect of the MoO3-doping on the performance and thermal stability of the QLEDs. We believe that QLEDs with the p-doped HTL can be used for further QLED researches to simultaneously improve the efficiency, lifetime, and high temperature stability, which are highly required for their use in automotive and outdoor displays.

Multifunctional RbCl dopants for efficient inverted planar perovskite solar cell with ultra-high fill factor, negligible hysteresis and improved stability

Interfacial engineering, especially for the hole transport layer (HTL) design, is a significant approach to improve photovoltaic performance of inverted planar perovskite solar cells (PSCs). Herein, we decorated the widely used HTL materials of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) through dispersing rubidium chloride (RbCl) in the aqueous solution. Based on systematic characterizations, we find that the RbCl dopant plays multiple roles in both the PEDOT:PSS-RbCl composite film and the interface between perovskite and HTL. RbCl could induce phase segregation of PEDOT:PSS and enlarge its nanocrystal size, which in turn to simultaneously enhance electrical conductivity, hole transport capability and work function without sacrificing optical transmittance of the HTL. In addition, RbCl crystallite possesses similar polyhedral structure and lattice parameters as the perovskite, which is beneficial for the seed-mediated growth of perovskite. The seed-mediated perovskite formation leads to a dense and uniform active layer with superior crystallinity and less trap density. Consequently, the PSCs with the doped HTL show remarkably enhanced performance for both the pure perovskite MAPbI3 (from 13.24% to 16.63%) and mixed perovskite MA0.7FA0.3Pb(I0.9Br0.1)3 (from 16.13% to 18.30%). Impressively, negligible hysteresis, high fill factor (FF, over 80%) and improved moisture stability are observed for both perovskites using the doped HTL.

Enhanced performance of perovskite solar cells using p-type doped PFB:F4TCNQ composite as hole transport layer

Conjugated polymers have been widely used as hole transport materials (HTM) in the preparation of mesoscopic perovskite solar cells (PSCs). In this work, we employed p-type doped conducting polymer known as poly(9,9-dioctylfluorene-co-bis-N,N-(-4-butyl phenyl)-bis-N,N-phenyl-1,4-phenylenediamine) (PFB) as a hole transport material (HTM) in perovskite based solar cell. The effect of dopant concentration on the optical and electrical properties of PEB was investigated to optimize the electrical properties of the material for the best function of the solar cell. The highest power conversion efficiency of mesoscopic perovskite solar cells (PSCs), fabricated in this investigation, was found to be 14.04% which is 57% higher than that of pristine PFB hole transport layer. The UV–Vis absorption and Raman spectroscopy measurements confirm the occurrence of oxidation in a p-type doped PFB hole transport layer. This is attributed to the transfer of electrons from the highest occupied molecular orbital (HOMO) of PEB to the lowest unoccupied molecular orbital (LUMO) of F4TCNQ. The solar cells produced using p-type doped PFB:F4TCNQ composite not only improves device performances but also shows superior long-term stability. The optical, morphological and electrical properties of the doped composite PFB: F4TCNQ and newly fabricated devices are presented and discussed in this paper.

Hole Extraction Enhancement for Efficient Polymer Solar Cells with Boronic Acid Functionalized Carbon Nanotubes doped Hole Transport Layers

Boronic acid functionalized multiwalled carbon nanotubes (bf-MWCNTs) were synthesized via a facile low temperature process and introduced in PEDOT:PSS as the composite hole transport layer (HTL), which improved the power conversion efficiency (PCE) of polymer solar cells (PSCs). The devices utilized PCDTBT:PC71BM active layers had achieved an optimal PCE of 6.953%, leading to 28% enhancement comparing to the device based on pristine PEDOT:PSS HTL. The PEDOT:PSS:bf-MWCNTs composite HTLs exhibited remarkable enhancement on hole mobility and electrical conductivity, which were beneficial to the hole extraction and transport on interface. Meanwhile, the work function (WF) of HTLs had an increase after bf-MWCNTs doping, which was matched with the highest occupied molecular orbital (HOMO) of the donor material, further improving the hole transport. Therefore, the incorporation of bf-MWCNTs efficiently improved the hole extraction and transport from active layer to the electrode.

Lifetime extension of blue phosphorescent organic light-emitting diodes by suppressing triplet-polaron annihilation using a triplet emitter doped hole transport layer

Abstract A lifetime extending device structure by suppressing positive polaron induced triplet exciton-polaron annihilation was developed for improved lifetime in blue phosphorescent organic light-emitting diodes. A blue triplet emitter doped hole transport layer was introduced to control the triplet exciton-polaron annihilation of blue phosphorescent emitters in the emitting layer, which extended the lifetime of the blue phosphorescent devices. Current and ultraviolet light/current aging tests of hole and electron only devices proved that the lifetime extending mechanism of the blue triplet emitter doped hole transport layer is suppression of triplet exciton-positive polaron annihilation.

Efficiency and stability enhancement of inverted perovskite solar cells via the addition of metal nanoparticles in the hole transport layer

Inverted perovskite solar cells with enhanced efficiency and stability are fabricated based on a nanoparticles doped hole transport layer.

Efficiency enhancement of fluorescent blue organic light-emitting diodes using doped hole transport and emissive layers

The electroluminescent characteristics of blue organic light-emitting diodes (BOLEDs) fabricated with doped charge carrier transport layers are analyzed. The fluorescent blue dopant BCzVBi is doped in an emissive layer, hole transport layer (HTL) and electron transport layer (ETL), respectively, to optimize the probability of exciton generation in the BOLEDs. The luminance and luminous efficiency of BOLEDs made with BCzVBi-doped HTL and ETL increase by 22% and 17% from 11,683 cd/m2 at 8.5 V and 6.08 cd/A at 4.0 V to 14,264 cd/m2 at 8.5 V and 7.13 cd/A at 4.0 V while CIE coordinates of (0.15, 0.15) of both types of BOLEDs remained unchanged. The electron mobility of BCzVBi is estimated to be 1.02×10−5 cm2/Vs by TOF.