Hole Transport Layer Research Articles

PEDOT:PSS-Free Quantum-Dot Light-Emitting Diode with Enhanced Efficiency and Stability.

Although high-performance quantum-dot light-emitting diodes (QLEDs) have been achieved, their stability is still limited due to the use of unstable PEDOT:PSS as the hole injection layer (HIL). Here, we developed a PEDOT:PSS-free QLED by using a binary PTAA:F4-TCNQ HIL. Because the PTAA, with a highest occupied molecular orbital (HOMO) level of ∼5.20 eV, can facilitate hole injection from ITO to the hole transport layer, and the F4-TCNQ can act as the electron acceptor dopant to improve the hole density and hole mobility of PTAA, the PTAA:F4-TCNQ HIL can exhibit excellent hole injection capability. As a result, the PEDOT:PSS-free QLED can exhibit a high EQE of 24.19% and an impressive brightness of 367,200 cd/m2, which are significantly higher than those of conventional QLEDs. Moreover, due to the improvement of device performance and the removal of PEDOT:PSS, the PEDOT:PSS-free QLED can also exhibit a high T95 operational lifetime of 4206 h at 1000 cd/m2 and an excellent T80 shelf lifetime of 207.41 h at 136400 cd/m2, which are about 1.6- and 3.3-fold those of conventional QLEDs, respectively. We believe that the demonstrated PEDOT:PSS-free QLED, with higher performance and stability, will promote the practical application of QLEDs in displays.

Optimization of Sr3NCl3-based perovskite solar cell performance through the comparison of different electron and hole transport layers

Strontium Nitride Trichloride (Sr3NCl3) is a promising absorber material for solar cells due to its unique structural, electrical, and optical properties. We conducted a thorough investigation to scrutinize the structural, optical, and electronic characteristics and the photovoltaic efficiency of double-heterojunction solar cells utilizing Sr3NCl3 absorbers. Various metals were evaluated for the front and rear contacts to determine the optimal metal-semiconductor interface, with the study determining that silver (Ag) is the most suitable option for the front contact and nickel (Ni) for the back contact. The PV performance of innovative Sr3NCl3 absorber-based cell structures was evaluated with two different Hole Transport Layers (HTLs), MASnBe3 and CBTS, alongside ZnO and WS2 serving as the transition metal dichalcogenide (TMD) Electron Transport Layers (ETLs). This investigation examined a range of factors, such as layer thickness, operational temperature, doping density, defect densities at both the interfaces and within the bulk, carrier generation and recombination rates, quantum efficiency (QE), series versus shunt resistance, absorption coefficient, and current density-voltage (J-V) characteristics, utilizing the SCAPS-1D simulator software. Fine-tuning of both two HTL and ETL revealed that the highest power conversion efficiency (PCE) of 27.34 % with JSC of 19.78 mA/cm2, fill factor (FF) of 88.84 %, and VOC of 1.56 V was achieved with MASnBe3 HTL and ZnO ETL, while the lowest PCE of 25.55 %, with JSC of 19.77 mA/cm2, FF of 89.07 %, and VOC of 1.45 V was obtained for CBTS HTL and WS2 ETL, respectively. These findings highlight the promising potential of Sr3NCl3 absorbers with ZnO as ETL and MASnBe3 as HTL for developing advanced perovskites heterostructure solar cells for enhanced performance in the future.

Efficient Perovskite Light Emitting Diodes Enabled by Mixed Ruddlesden–Popper (RP) Perovskite–Perovskite Planar Heterojunction between Hole Transport and Emission Layers

Efficient Perovskite Light Emitting Diodes Enabled by Mixed Ruddlesden–Popper (RP) Perovskite–Perovskite Planar Heterojunction between Hole Transport and Emission Layers

Modification of solar energy and photoelectrochemical water splitting properties: using FTO/Er-TiO2/MAPbI3/CuPc/Au as modified photoelectrode

In the past decades, converting solar energy into hydrogen through photoelectrochemical water splitting has been attracted. Here, we designed a new FTO/Er-TiO2/MAPbI3/CuPc/Au photoanode with n-i-p structure for using in solar water splitting. Accourding to obtained PEC results, the FTO/Er-TiO2/MAPbI3/CuPc/Au photoanode has a photocurrent density of ∼9.8 mA cm−2 ( under a visible lamp with intensity of 100 mW cm−2 irradiation) compared to FTO/Er-TiO2/Au and FTO/Er-TiO2/MAPbI3/Au photoanodes with photocurrent density of 0.7 and 6.12 mA cm−2, respectively. This important enhancement is refered to the light absorption feature of Er-TiO2/MAPbI3 and a fast electron and hole transfer process in the Er-TiO2 and CuPc, respectively. The photoelectrochemical action of the photoelectrode is increased using erbium doping due to creation of oxygen vacancies and titanium (III) ions. Furthermore, in this research, we studided the power conversion efficiency (PCE) of FTO/Er-TiO2/MAPbI3/Au and FTO/Er-TiO2/MAPbI3/CuPc/Au solar cells. The results shown that the significant enhancement in photovoltaic properties can be observed by utilizing spin-coated CuPc nanoparticles (as hole transport layer) at least by 1.39% compared to the FTO/Er-TiO2/MAPbI3 perovskite solar cell.

High-Throughput Screening, Crystal Structure Prediction, and Carrier Mobility Calculations of Organic Molecular Semiconductors as Hole Transport Layer Materials in Perovskite Solar Cells

High-Throughput Screening, Crystal Structure Prediction, and Carrier Mobility Calculations of Organic Molecular Semiconductors as Hole Transport Layer Materials in Perovskite Solar Cells

Tailoring Perovskite/C60 Interface by Reactive Passivators for Stable Tandem Solar Cells

AbstractIntegrating perovskite solar cells with crystalline silicon bottom cells in a monolithic two‐terminal tandem configuration enables power conversion efficiency (PCE) surpassing the theoretical limits of single‐junction cells. However, wide bandgap (WBG) perovskite films face challenges related to phase stability and open circuit voltage (VOC) deficit, particularly due to severe non‐radiative recombination at the perovskite/C60 interface. Here, the interfacial defects are passivated by incorporating a reactive passivator that reacts with lead halides to form low‐dimensional phases. The target product obtained by optimizing the reaction temperature not only suppresses recombination across the interface, but also facilitates the transfer of charge carriers. More importantly, this product can suppress phase segregation of WBG perovskite films under exposure to light illumination and moisture. This strategy enables a high VOC of 1.25 V for WBG perovskite device based on polymer hole transport layer and a certified stabilized PCE of 30.52% for a monolithic perovskite/silicon tandem solar cell. The unencapsulated tandem device retains 94% of its initial PCE over 200 h under continuous 1‐sun full spectrum illumination in air, demonstrating the improved phase stability.

Achieving High Doping Density in pH-neutral Conjugated Polyelectrolyte Toward Effective Hole-Transporting Materials for Organic Solar Cells.

The lack of effective and non-corrosive hole-transporting layer (HTL) materials has remained a long-standing issue that severely restricts the performance of organic solar cells (OSCs). Most pH-neutral conjugated polyelectrolytes (CPEs) exhibit inferior performance to the acid-doped HTL materials due to their low doping density. In this study, a series of pH-neutral CPEs is designed and synthesized with high doping density as HTL materials. Through an elaborate synthetic route, two sulfonate-terminating alkoxyl side chains can be introduced into thiophene, by which the electron-rich, highly soluble, and chemically stable thiophene monomer is synthesized to enable the subsequent polymerization. The CPE PTT-F exhibit a remarkable self-doping property with an enhanced doping density from 2.01 × 1017 to 7.02 × 1018 cm-3. The high work function and the increased doping density of PTT-F-based HTL decrease the depletion region width from 38.4 to 8.1nm at the anode interface, which minimized the energy loss in hole transport. Consequently, a binary OSC modified by PTT-F-based HTL achieve a high PCE of 18.8%. To the best of the knowledge, this is the highest PCE for OSC employing CPE-based HTL. The results from this work demonstrate an encouraging achievement of realizing exceptional hole collection ability in pH-neutral CPEs.

High Performance Perovskite Solar Cells Based on Multifunctional Additives of Crown‐Ether‐Iodine Supra‐Molecules

AbstractThe efficiency and stability of perovskite solar cells (PSCs) are influenced by various factors, such as controlling the migration of iodide anion (I−) and lithium cation (Li+), oxidizing the hole‐transport material of 2,2′,7,7′‐tetras(N,N‐p‐methoxyaniline)‐9,9′‐spirodifluorene (Spiro), and passivating the perovskite film. Herein, three multifunctional crown‐ether‐iodine (crown‐ether‐I2) supra‐molecules are investigated as activities in the hole transport layers (HTLs). Results indicate that the crown‐ether‐I2 can slowly release I2 to gently oxidize Spiro, and significantly improve the efficiency of PSCs. Moreover, the crown‐ether can contribute to stabilizing Li+ in HTL and passivating the defect sites on the upper interface of the perovskite layer, which can enhance the long‐term stability of PSCs. Furthermore, crown‐ether‐I2 can absorb I− to produce crown‐ether‐I3−, which can discharge I− to promote the self‐healing of I− defects and inhibit the migration of I− in the perovskite film, thereby further enhancing PSC's long‐term stability. PSC based on Dbenzo‐24‐Crown‐8‐Ether‐Iodine (DB24C8‐I2) achieves an impressive efficiency of 24.29%, which is much higher than that of the control device (22.28%). Additionally, the stability of the un‐encapsulated PSC with DB24C8‐I2 is significantly enhanced, while maintaining 96.9% of its original efficiency after 2000 h. This work provides an effective strategy for improving the efficiency and long‐term stability of PSCs.

Controlling Polarization‐Induced Polaron Accumulation in OLEDs via Device Design

AbstractSpontaneous alignment of molecular electric dipole moments, known as spontaneous orientation polarization (SOP), is present in many organic electronic materials. The SOP‐induced field changes the internal voltage distribution within the device, altering polaron injection and accumulation. The important role of SOP in organic light‐emitting devices (OLEDs) has recently been emphasized with clear links between dipole alignment and device efficiency and operational lifetime. Prior work has thus sought to engineer SOP via changes in thin film composition or processing conditions. These efforts have generally been directed at the OLED electron transport layer, which can show strong SOP. This work takes a different approach, focusing instead on how changes in device architecture can be applied to tune the magnitude and dynamics of polaron accumulation in response to SOP. In this work, it is demonstrated that the introduction of SOP into the device emissive layer offers control over the spatial location of accumulation. In parallel, insertion of a spacer layer between the hole transport and emissive layers can be used to tune the polaron accumulation rate and density during device operation. Both of these architectural changes permit an increase in OLED efficiency and a pathway around the deleterious impact of SOP‐induced polaron accumulation.

Conformal SnO2 and NiOx charge transport layers for pragmatic air-processed perovskite solar cells

The industrialization of perovskite (PVK) solar cells (PSCs) necessitates simple manufacturing, cheapness, nontoxicity, high efficiency, and stability. We report an air-processed lead halide PSCs with cheap, nontoxic, stable NiOx and SnO2 as the hole and electron transport layers separately, to meet all the above commercial requests. By preparing the NiOx (water-dispersible) and SnO2 (oil-dispersible) quantum dots (QDs) with good conductivity and energy band matched well with that of PVK, we fabricate inverted PSCs (ITO/NiOx/PVK/SnO2/Ag) with efficiency up to 20.1/14.6% for active areas of 0.0707/1 cm2, under 1 sun simulated illumination with enhanced UV light ratio. The UV-light resistant PSCs reported here will impel their application in the high altitude areas with strong UV light. Importantly, the monodisperse size and dominant (110) plane of SnO2 QDs achieved by controlling the solvothermal parameters, realize the conformal deposition and defect prevention of SnO2, respectively, thus improving the PSC efficiency and stability.

High-performance wide-bandgap perovskite solar cells using poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) as the electron-transport layer

We used work-function-tuned poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) as the electron-transport layer for wide-bandgap (1.74 eV) perovskite solar cells (PSCs). With the coating of polyethylenimine, the work function of PEDOT:PSS was modified from −5.03 to −4.05 eV, which enabled efficient electron transportation from perovskite absorber to cathode. With this technique, the standard-structured n-i-p PSCs showed an average power-conversion-efficiency (PCE) of 18.6 %, which is higher than that (17.5 %) of inverted PSCs with PEDOT:PSS as the hole-transport layer. Moreover, the long-term stability of the PSCs was enhanced with the PCE degradation significantly suppressed from 29.7 % to 15.6 % after a 10 days’ measurement in ambient.

Reaction Dynamics between Formamidinium Lead Iodide and Copper Oxide.

Copper oxide (CuOx) has been announced as a very promising hole-transporting layer for perovskite solar cells. However, in our previous work, we have shown that once a formamidinium lead triiodide (FAPI) perovskite is spin-coated on a spray-coated cuprous oxide (Cu2O) substrate, the Cu2O diffuses into and reacts with the FAPI film. In order to verify if the degradation products are related to the oxidation state of CuOx and/or its preparation method, in this work, we first prepared CuOx films by thermal oxidation at temperatures ranging from 120 to 300 °C. While increasing the process temperature, a transformation from copper I (Cu2O) to copper II (CuO) oxidation states was observed. For both oxidation states of copper, FAPI perovskite degradation was found; however, some alterations in the reaction products were noticed. In contrast to our expectations, the introduction of an ultrathin plasma-enhanced atomic layer deposited Al2O3 layer in between both films only partially blocked the CuOx migration into the FAPI film. It can be concluded that regardless of the chemical composition and/or preparation method of CuOx, the overlayered FAPI film gets decomposed. In order to use CuOx as a hole-transporting layer in solar cells, new strategies must be developed to limit these unwanted chemical reactions.

Regulation of the Buried Interface to Achieve Efficient HTL-Free All-Inorganic CsPbI2Br-Based Perovskite Solar Cells.

The large voltage loss (Vloss) mainly stems from the mismatch between the perovskite film and electron transport layer in CsPbI2Br-based all-inorganic perovskite solar cells (I-PSCs), which restricts the power conversion efficiency (PCE) of devices. To address this issue, potassium benzoate (BAP) is first introduced as a bifunctional passivation material to regulate the TiO2/CsPbI2Br interface, reduce the Vloss, and improve the photovoltaic performance of CsPbI2Br-based I-PSCs. Eventually, the champion PCE of CsPbI2Br-based I-PSCs without a hole transport layer modified by BAP (Target-PSCs) improves to 14.90% from the 12.14% of reference PSCs. The open-circuit voltage (Voc) increases to 1.27 V from the initial 1.14 V after BAP modification. A series of characterizations show that BAP modification can not only optimize the energy level alignment of I-PSCs but also passivize the surface defects caused by uncoordinated Cs+/Pb2+. Moreover, the Target-PSCs without encapsulation demonstrate better thermal stability, which can maintain 107.6% of the original PCE after annealing at 160 °C for 140 min in humid air. While the reference PSCs only maintain 76.5% of their initial PCE after annealing at the same process. This work provides a simple strategy to modify the buried interface and improve the performance of CsPbI2Br-based I-PSCs.

Enhancing SrZrS3 perovskite solar cells: A comprehensive SCAPS-1D analysis of inorganic transport layers

In the quest for sustainable energy, perovskite solar cells have emerged as promising candidates due to their high power conversion efficiencies and excellent optoelectronic properties. This study focuses on SrZrS3, a lead-free chalcogenide perovskite, and its integration with various inorganic transport layers for enhanced photovoltaic performance. Using SCAPS-1D simulation software, the effects of different electron transport layers (ETLs) and hole transport layers (HTLs) on device efficiency were systematically explored. The device with a-Si:H as the HTL and ZnS as the ETL (aSi-3) shows the highest efficiency of 20.01 % resulting from better energy band alignment and reduced recombination losses. This study highlights the importance of optimizing transport layers for enhancing SrZrS3-based solar cells, offering insights for developing high-performance, lead-free perovskite solar cells.

Numerical investigation of graphene derivatives as HTL in PBDB-T:NCBDT bulk heterojunction organic solar cell

The damaging effects of the most widely used PEDOT:PSS have led researchers to search for an alternative hole transport layer (HTL) in non-fullerene acceptor (NFA) based bulk heterojunction organic solar cells (BHJOSC’s). This work highlights the numerical simulation study of possible new approach of utilizing graphene, graphene oxide (GO), reduced graphene oxide (rGO), and p type doped graphene (p-graphene), as an alternative to PEDOT:PSS in non-fullerene acceptor based bulk heterojunction organic solar cell (NFABHJOSC) with PBDB-T as donor and NCBDT as acceptor using SCAPS1D. NCBDT is an emerging small-molecule non-fullerene acceptor (SM-NFA) whose bandgap can be tuned and reduced, making it a better option as an acceptor. Validation of the software is done by matching simulation results with experimental results. Diverse electron transport layers (ETL’s), including PDINO, ZnO, IGZO, TiO2, TiO2:gr (20%) composite, and TiO2:gr (10%) composite, are introduced, and device performance of various configurations is analysed. Optimization of the best device configuration ITO (4.8 eV)/rGO/PBDB-T:NCBDT/PDINO/Al gave an improved efficiency of 17.47%, fill factor (FF) of 77.45%, short circuit current density (Jsc) of 25.407 mA/cm2, and an open circuit voltage (Voc) of 0.8878 V.

Functionalized porphyrin as a carrier bridge and a passivator for perovskite solar cells

Interfacial modification becomes one of the most emerging strategies in the state-of-the-art perovskite solar cells (PSCs). Here, two porphyrin derivatives (p-MeOTPP, m-DMeOTPP) with different methoxy groups are employed as the modifiers between perovskite and the hole transporting layer (HTL). The interaction at both of perovskite/modifier and modifier/HTL interfaces, and the hole-transfer ability of the modifier molecule are comprehensively studied, which are jointly responsible for the significant improvement in the optoelectronic properties of the device. More importantly, discussion on a molecular level reveals the distinct roles of modifiers with highly similar structures. A highest power conversion efficiency (PCE) of 24.56% is achieved for m-DMeOTPP modified PSCs, which is attributed to a synergy of efficient passivation effect at perovskite/modifier interface, sufficient built-in potential at modifier/HTL interface and minimal reorganization energy of hole hopping process. p-MeOTPP has a stronger passivation ability, but causes unfavorable interfacial dipole at modifier/HTL interface and a large energy barrier when hole’s hopping, only resulting in a smaller enhancement. Additionally, both modifers improve the device stability by strongly suppress the immigration of iodine species and moisture penetration. This work presents a synergy mechanism for interfacial engineering to pursue PSCs with high efficiency and stability, and provides practical guidelines at a molecular level to design a modifier not only as an efficient passivator but also as a high-speed carrier bridge.

Enhanced Carrier Selectivity and Superior Passivation in Cost‐Effective Heterogeneous Hybrid Transport Layers for Next Generation Silicon Solar Cells

AbstractHybrid hole transport layers (HHTLs) consisting of‐a low‐cost, low‐temperature, dopant‐free, organic, hole‐selective poly(3,4‐ethylenedioxythiophene):polystyrene sulphonate (PEDOT:PSS) and an inorganic homogenous tunnel oxides (HoTOs), such as SiOx, TiOx, and AlOx have allowed significant improvements in carrier selectivity as well as in power and cost efficiency. These key parameters can be further improved by introducing heterogeneous tunnel oxides (HeTOs), formed of two different inorganic oxides. This work examines the potential of heterogeneous HHTLs and their impact on passivation as well as on the interfacial properties in silicon solar cells. HeTOs of SiOx/TiOx and SiOx/AlOx with negative fixed charge are studied and optimized. A heterogeneous HHTL with AlOx (>1.5 nm) resulted in a high lifetime (1.2 ms), low surface recombination velocity, and improved surface band bending at the interface due to the presence of higher negative fixed charge (1012 cm−2) within these layers. The passivation properties further improved on light soaking and annealing due to oxidation of PSS and AlOx/SiOx. Overall, these HHTLs demonstrated a hole selectivity (S10) of 12.5 and very high efficiencies up to of 26.1%, surpassing homogenous‐SiOx/PEDOT:PSS by 1.4%.

Inverted All-Inorganic Nanorod-Based Light-Emitting Diodes via Electrophoretic Deposition.

High performance and high stability in all-inorganic solution processed nanocrystal-based light-emitting diodes (LEDs) are highly attractive for large area devices compared to organic material-based LEDs. In this work, an inverted all-inorganic LED structure is designed to have an easy integration with thin-film transistors. Adopting robust inorganic materials such as Ni1-x O nanoparticle films as a hole transport layer (HTL) is beneficial for the performance of LED. Herein, we have optimized the HTL by introducing Mg into Ni1-x O to bridge the difference in energy offset between the nanorod emissive layer and the HTL, in addition to the advantages of low temperature solubility of Ni1-x O:Mg nanoparticles. Furthermore, CdSe/CdS-based nanorods via electrophoretic deposition (EPD) are amassed in a vertically aligned (VA-NR) fashion as an emissive layer to facilitate the carrier transportation. Fostering these approaches enabled an EQE of 1.2% of the fabricated device, establishing the viability for further development of efficient and highly stable nanocrystal-based LEDs.

Transient Leakage Electroluminescence of Quantum-Dot Light-Emitting Diodes.

Parasitic emission or leakage emission caused by electron leakage to a hole transport layer in quantum-dot light-emitting diodes (QLEDs) critically impacts device efficiency and operational stability. The buildup dynamics of such emission channels, however, was insufficiently researched. Herein, we investigate transient electroluminescence dynamics of leakage emission in red/green/blue (R/G/B) QLEDs and reveal notable contrast for R and G. In RQLEDs, leakage emission exhibits delayed turning-on than primary emission, which is attributed to much slower filling up from lower-energy electron states and the initial quenching by nonradiative recombination with trapped holes. For GQLEDs, leakage emission turns on much more concurrently, and emission preferably starts from higher energy states. For R/G QLEDs, under varied offset voltage modulation, the current efficiency of primary emission is invert-correlated to leakage emission, reconfirming leakage emission as a loss indicator.

Organic Salt Buffer Layer Enables High‐Performance NiOx‐Based Inverted Perovskite Solar Cells

The merits of a low‐cost fabrication process, suitable band structure, excellent wettability to perovskite precursor, and outstanding stability ensure NiOx as a hole transport material with beneficial characteristics to construct high‐performance perovskite solar cells (PSCs). However, direct contact between perovskite and NiOx causes delamination and chemical instability and thus results in poor carrier transport and short device lifespan. Here, we propose a solution for this issue by introducing an organic salt additive 4‐(trifluoromethyl) benzylammonium formate (TFMBAFa) in the perovskite precursor to passivate perovskite film and NiOx@(2‐(3,6‐dimethyl‐9H‐carbazol‐9‐yl) ethyl) phosphonic acid (Me‐2PACz) composited hole transport layer (HTL), and thus construct a buffer layer between perovskite‐HTL interface. The effective diminishing of NiOx/perovskite interfacial reactions and defects results in enhanced carrier transport. Consequently, the target device achieves simultaneous improvements in power conversion efficiency (24.2%), storage stability (T100 > 1400 h), thermal stability (T80 > 1000 h), and operational stability (T70 > 850 h), where T100, T80, and T70 refer to the retention of 100%, 80%, and 70% of initial PCE, respectively. This work provides an effective strategy to advance the performance of NiOx‐based inverted PSCs.