NiOx Hole Transport Layer Research Articles

Bilateral Embedded Anchoring via Tailored Polymer Brush for Large-Area Air-Processed Blue Light-Emitting Diodes.

Perovskite light-emitting diodes (PeLEDs) that can be air-processed promises the development of displaying optoelectronic device, while is challenged by technical difficulty on both the active layer and hole transport layer (HTL) caused by the unavoidable humidity interference. Here, we propose and validate that, planting the polymer brush with tailored functional groups in inorganic HTL, provides unique bilateral embedded anchoring that is capable of simultaneously addressing the n phases crystallization rates in the active layer as well as the deteriorated particulate surface defects in HTL. Exemplified by zwitterionic polyethyleneimine-sulfonate (PEIS) in present study, its implanting in NiOx HTL offers abundant nuclei sites of amino and sulfonate groups that balance the growth rate of different n phases in quasi-2D perovskite films. Moreover, the PEIS effectively nailed the interfacial contact between perovskite and NiOx, and reduced the particulate surface defects in HTL, leading to the enhanced PLQY and stability of large-area blue perovskite film in ambient air. By virtue of these merits, present work achieves the first demonstration of the air-processed blue PeLEDs in large emitting area of 1.0 cm2 with peak external quantum efficiency (EQE) of 2.09 %, which is comparable to the similar pure-bromide blue PeLEDs fabricated in glovebox.

Bilateral Embedded Anchoring via Tailored Polymer Brush for Large‐Area Air‐Processed Blue Light‐Emitting Diodes

AbstractPerovskite light‐emitting diodes (PeLEDs) that can be air‐processed promises the development of displaying optoelectronic device, while is challenged by technical difficulty on both the active layer and hole transport layer (HTL) caused by the unavoidable humidity interference. Here, we propose and validate that, planting the polymer brush with tailored functional groups in inorganic HTL, provides unique bilateral embedded anchoring that is capable of simultaneously addressing the n phases crystallization rates in the active layer as well as the deteriorated particulate surface defects in HTL. Exemplified by zwitterionic polyethyleneimine‐sulfonate (PEIS) in present study, its implanting in NiOx HTL offers abundant nuclei sites of amino and sulfonate groups that balance the growth rate of different n phases in quasi‐2D perovskite films. Moreover, the PEIS effectively nailed the interfacial contact between perovskite and NiOx, and reduced the particulate surface defects in HTL, leading to the enhanced PLQY and stability of large‐area blue perovskite film in ambient air. By virtue of these merits, present work achieves the first demonstration of the air‐processed blue PeLEDs in large emitting area of 1.0 cm2 with peak external quantum efficiency (EQE) of 2.09 %, which is comparable to the similar pure‐bromide blue PeLEDs fabricated in glovebox.

Solvent management and Li+/Mg2+ co-doping enable efficient n-i-p NiOx-based perovskite solar cells

Spin-coating pre-fabricated NiOx nanocrystals using an annealing-free process is a compatible technique for fabricating the hole transport layer in n-i-p structured perovskite solar cells. The solvothermal method, assisted by long-chain fatty acids or amines such as oleic acid and oleylamine, has demonstrated the applicability of fabricating NiOx nanoparticles with uniform morphology and size. However, the long-chain fatty acids or amines covering the NiOx nanoparticles cannot be removed at low temperature, obstructing the transport of photo-generated holes due to their insulating characteristics. Herein, triphenylphosphine is employed to replace a portion of oleylamine in the solvothermal reaction solution. Experimental results demonstrate that the introduction of triphenylphosphine does not affect the dispersion of the synthesized NiOx nanoparticles in toluene. The as-fabricated n-i-p structured device receives an efficiency of 12.63 %. Thereafter, Li+ doping and Li+-Mg2+ co-doping strategies are used to further enhance the devices' performance. The best-behaved device with Li+-Mg2+ co-doping NiOx hole transport layer acquires an efficiency of 16.20 %. This research provides a practical approach for fabricating efficient NiOx hole transport materials for n-i-p structured perovskite solar cells.

Exploration and Optimization of the Polymer-Modified NiOx Hole Transport Layer for Fabricating Inverted Perovskite Solar Cells.

The recombination of charge carriers at the interface between carrier transport layers such as nickel oxide (NiOx) and the perovskite absorber has long been a challenge in perovskite solar cells (PSCs). To address this issue, we introduced a polymer additive poly(vinyl butyral) into NiOx and subjected it to high-temperature annealing to form a void-containing structure. The formation of voids is confirmed to increase light transmittance and surface area of NiOx, which is beneficial for light absorption and carrier separation within PSCs. Experimental results demonstrate that the incorporation of the polymer additive helped to enhance the hole conductivity and carrier extraction of NiOx with a higher Ni3+/Ni2+ ratio. This also optimized the energy levels of NiOx to match with the perovskite to raise the open-circuit voltage to 1.01 V. By incorporating an additional NiOx layer beneath the polymer-modified NiOx, the device efficiency was further increased as verified from the dark current measurement of devices.

Sensitive and Low-Noise Perovskite Nanocrystal-Organic Bulk Heterostructure X-ray Detectors Enabled by Sodium Bromide-Assisted In Situ Reparation.

Perovskite nanocrystals (PNCs) offer unique advantages in large-area and thick-film deposition for X-ray detection applications due to the decoupling of the crystallization of perovskite from film formation, as well as their low-temperature and scalable deposition methods. However, the partial detachment of long-chain ligands in PNCs during the purification process would lead to the exposure of surface defects, making it challenging to ensure efficient charge carrier extraction and stable X-ray detection. In this study, we propose a beneficial strategy that involves the in situ reparation of these exposed defects with sodium bromide (NaBr) during the purification process to construct CsPbBr3 PNC-organic bulk heterostructure X-ray detectors. The NaBr-passivated PNCs exhibit stronger photoluminescence intensity and lower trap density in films compared to those of the control samples, confirming the effective passivation of halide vacancy defects. Furthermore, the NiOx hole transport layer with remarkable electron blocking capability is introduced to further suppress the dark current of the devices. Consequently, the optimal devices exhibit a large sensitivity of 4237 μC Gyair-1 cm-2 and a low dark current density of 10 nA cm-2, as well as improved operational stability, which allows for high-contrast and low-dose X-ray imaging applications.

Praseodymium doped nickel oxide as hole-transport layer for efficient planar Perovskite Solar Cells

Hybrid organic/inorganic perovskite solar cells (PSCs) have acquired significant consideration due to high power conversion efficiency (PCE). In PSCs, electron and hole extraction layers have a significant influence on their overall performance. In inverted p-i-n structure-based PSCs, NiOx has been frequently employed as a hole transport layer (HTL) due to its simple processing, wide bandgap, high optical transmittance, excellent chemical stability, and low processing temperature for large-scale fabrication. However, NiOx suffers from low electrical conductivity. Doping of NiOx is an effective technique employed for enhancing electrical as well as optical properties. Herein, the praseodymium doped NiOx (Pr-NiOx) was synthesized by sol-gel method, and films were fabricated to investigate the effect of Pr dopant on the optoelectronic properties and photovoltaic performance of PSCs. Results indicated that Pr doping significantly improved the hole mobility by about threefold and conductivity of NiOx films from 4.68 × 10-6 S cm-1 to 8.27 × 10-6 S cm-1. Moreover, it also enhanced the compactness and interfaces of NiOx HTL. PSCs based on 4 % Pr-doped NiOx HTL- yielded PCE of 9.35 % which is 32.43 % more than the PSCs fabricated using undoped NiOx HTL. The enhanced PCE of PSC devices with Pr-doped NiOx could be attributed to efficient extraction of a hole from an active absorbing layer of perovskite thereby, lowering the probability of unsuitable charge carrier recombination. This work exhibits that Pr-doped NiOx thin film could be a promising alternative material for efficient and stable inverted PSCs.

Critical role of dopant in NiOx hole transport layer for mitigating redox reactivity at NiOx/absorber interface in mixed cation perovskite solar cells.

Redox chemistry transpiring at the interface of NiOx hole transport layer (HTL) and perovskite absorber is a critical phenomenon leading to relatively low values of open circuit voltage (VOC) and fill factor (FF), in turn hampering the overall device performance and stability. In this work, for the first time, the hard acid electronic nature of vanadium (V) dopant in nickel oxide HTL is opportunely exploited to mitigate the undesirable Lewis acid-base reactions occurring at the HTL/mixed-cation perovskite interface. The findings of the study show that vanadium doping results in improved interfacial energetics along with decreased VOC loss, confirming that despite the increase in Ni3+/Ni2+ ratio with the vanadium dopant, the redox reaction catalyzed by Ni3+ ions is kept under check. Vanadium doping also aided in the realization of superior perovskite films with lower Urbach energy, which translated into one order increase in maximum photoinduced carrier generation rate per unit volume. Carrier dynamics investigations show fewer defect states (lower VTFL) and trap-assisted recombination (lower diode ideality factor), which optimize the devices' photovoltaic performance. These benefits collectively contribute to low-loss charge transfer across the NiOx/mixed-cation perovskite interface, which increases the relative efficiency by ∼30% for 5 wt% V-doped NiOx devices compared to pristine NiOx devices, augmented by an increase in device J-V parameters like open circuit voltage (VOC), short circuit current density (JSC), and fill factor (FF).

Halogen doping of p-type inorganic hole transport layer: electronic nature-based dopant engineering for modulating hole selectivity in inverted planar perovskite solar cells

The role of metal cation and halide anion dopants in regulating the properties of NiOx hole transport layer (HTL) was explored. This study confirms that halide dopants also increase the Ni3+ defect density and work function of p-type inorganic HTL.

Enhancing Efficiency of Inverted Perovskite Solar Cells by Sputtered Nickel Oxide Hole‐Transport Layers

Perovskite solar cells (PSCs) are now approaching their theoretical limits and the optimization of the auxiliary layers is crucial for fully exploiting the potential of perovskite materials. In this study, NiOx as a hole‐transport layer (HTL) for inverted p–i–n PSCs is focused on. Sputtered NiOx is an attractive p‐type HTL owing to its facile processing, wide energy bandgap that prevents electron transfer, high transparency, stability, and effective hole extraction. Despite substantial research on sputtered NiOx, the relationship between the carrier concentration and work function is still unclear. In this study, the use of sputtered NiOx as a widely compatible HTL and the effect of its thickness on PSC device performance are investigated. Inverted PSCs with the optimal 10 nm thick NiOx achieve a remarkable power conversion efficiency of 20.54%, which is the highest reported to date for sputtered NiOx‐based PSCs. Furthermore, PSCs with various NiOx thicknesses demonstrate similar performances, demonstrating the excellent versatility of NiOx for use with different perovskite absorbers. The devices exhibit excellent thermal and photostability, retaining 97% of their initial power conversion efficiency at 65 °C and 1 sun illumination for 350 h. Sputtered NiOx HTLs have great potential for use with diverse perovskite compositions and PSC structures.

Enhancement of Interfacial Properties by Indoloquinoxaline‐Based Small Molecules for Highly Efficient Wide‐Bandgap Perovskite Solar Cells

AbstractInterfacial engineering in organic–inorganic hybrid perovskite solar cells (PSCs) has attracted significant attention, aiming to achieve high‐performing and highly stable devices. Here, newly designed organic small molecules based on quinoxaline and triphenylamine for inverted type wide‐bandgap PSCs are introduced, with the objective of enhancing the interfacial properties between perovskite and NiOx hole transport layer (HTL). The incorporation of an organic interlayer effectively reduces the energy level offset between the HTL and wide‐bandgap perovskite, while passivating defects within the perovskite layer. It leads to improved charge extraction and minimized non‐radiative recombination at the interface. Furthermore, the enhanced interfacial characteristics and hydrophobicity contribute to the improvement of perovskite film quality, resulting in larger grain size and higher crystallinity. As a result, the power conversion efficiency (PCE) of the PSC is enhanced from 18.9% to 20.1% with the incorporation of the IQTPAFlu interlayer, accompanied by an increase in Voc to ≈1.3 V, achieving a significantly low Voc deficit of 0.46 V. And the IQTPAFlu‐based devices demonstrate stable and consistent performance over 500 h, with ≈91% of their initial PCE retained. The highly stable wide‐bandgap PSCs, characterized by high Voc and PCEs, hold great promise as potential candidates for tandem solar cells.

Dipole-tunable interfacial engineering strategy for high-performance all-inorganic red quantum-dot light-emitting diodes

All-inorganic quantum dot (QD) light-emitting diodes (AI-QLEDs) with excellent stability received enormous interest in the past few years. Nevertheless, the vast energy offset and the high trap density at the NiOX/QDs interface limit hole injection leading to fluorescence quenching and hampering the performance. Here, we present self-assembled monolayers (SAMs) with phosphonic acid (PA) anchoring groups modifying NiOX hole transport layer (HTL) to tune energy level and passivate trap states. This strategy facilitates hole injection owning to the well-aligned energy level by interface dipole, downshifting the vacuum level, reducing the hole injection barrier from 0.94 eV to 0.28 eV. Meanwhile, it mitigates the interfacial recombination by passivating surface hydroxyl group (-OH) and oxygen vacancy (VO) traps in NiOX. The electron leakage from QDs toward NiOX HTL is significantly suppressed. The all-inorganic R-QLEDs exhibit one of the highest maximum luminance, external quantum efficiency and operational lifetime of 88980 cd m−2, 10.3 % and 335045 h (T50 @100 cd m−2), respectively. The as-proposed interface engineering provides an effective design principle for high-performance AI-QLEDs for future outdoor and optical projection-type display applications.

Mild oxygen plasma-treated nickel oxides for performance enhancement of hybrid perovskite light-emitting diodes

Nickel oxide (NiOx), a representative transparent p-type semiconductor, has been a promising candidate for hole transport layer (HTL) in perovskite-based photovoltaic and light-emitting diode (LED) devices due to its high chemical stability and high transparency. However, the interface between the NiOx and perovskite emission layers shows a relatively large electrical barrier for the holes to be transported, which degrades the interfacial electrical properties. To overcome these problems, we suggest a mild oxygen plasma treatment on the NiOx surface to introduce Ni vacancies while retaining its advantages. By controllably forming the Ni vacancies, the hole concentrations could be controlled, which modulated the valence band edge level. This increases the work function of NiOx from 4.979 to 5.364 eV, which facilitates the hole transport at the interface between NiOx HTL and the perovskite emission layer. Ultimately, the overall process leads to improved electroluminescence intensity, reduced driving voltage reduction, and low charge trap density at the interface between the NiOx HTL and the perovskite emission layers. These eventually improved the external quantum efficiency of the perovskite light-emitting diodes.

Highly stable all-inorganic CsPbBr3 perovskite solar cells based on pulsed laser deposition

In the highly efficient n-i-p structure of perovskite solar cells (PSCs), organic material Spiro-OMeTAD is usually used as the hole transport layer (HTL). However, its high hygroscopicity and thermal instability seriously limit its commercial application. In contrast, nickel oxide (NiOx) is a promising alternative due to its wideband gap, low cost, and high stability. By comparing with traditional spin coating, pulsed laser deposition (PLD) can produce relatively compact films and avoid the damage of solvent evaporation on the morphology and crystal quality, thus improving the device stability. This work introduces PLD to prepare CsPbBr3 and NiOx thin films to obtain highly stable all-inorganic CsPbBr3-based PSCs. Carrier dynamics are studied via electrochemical measurements and transient absorption spectroscopy. The power conversion efficiency of the all-inorganic CsPbBr3-based PSCs with NiOx HTL can be improved to 5.47% under optimum thickness and annealing temperature. It is revealed that the thermal stability is significantly enhanced, where unencapsulated all-inorganic CsPbBr3 PSCs specifically can maintain 95% of initial efficiency for 1200 h under the condition of 85 °C and 30% relative humidity.

Facile Modification on Buried Interface for Highly Efficient and Stable FASn0.5Pb0.5I3 Perovskite Solar Cells with NiOx Hole‐Transport layers†

Comprehensive SummaryFormamidinium (FA)‐based Sn‐Pb perovskite solar cells (FAPb0.5Sn0.5I3 PSCs) with ideal bandgap and impressive thermal stability have caught enormous attention recently. However, it still suffers from the challenge of realizing high efficiency due to the surface imperfections of the transport materials and the energy‐level mismatch between functional contacts. Herein, it is demonstrated that the modification on buried interface with alkali metal salts is a viable strategy to alleviate these issues. We systematically investigate the role of three alkali metal bromide salts (NaBr, KBr, CsBr) by burying them between the NiOx hole transport layer (HTL) and the perovskite light‐absorbing layer, which can effectively passivate interface defects, improve energy‐level matching and release the internal residual strain in perovskite layers. The device with CsBr buffer layer exhibits the best power conversion efficiency (PCE) approaching 20%, which is one of the highest efficiencies for FA‐based Sn‐Pb PSCs employing NiOx HTLs. Impressively, the long‐term storage stability of the unencapsulated device is also greatly boosted. Our work provides an efficient strategy to prepare desired FA‐based ideal‐bandgap Sn‐Pb PSCs which could be applied in tandem solar cells.

Unlocking The Role of Guanidinium Salts in Interface Engineering for Boosted Performance of Inverted Perovskite Solar Cells.

NiOx-based inverted perovskite solar cells (PSCs) have attracted growing attention due to their low cost and large-scale application potential. However, the efficiency and stability of inverted planar heterojunction PSCs is still unsatisfactory owing to insufficient charge-extraction caused by undesirable interfacial contact between perovskite and NiOx hole transport layers (HTLs). Herein an interfacial passivation strategy with guanidinium salts (guanidinium thiocyanate (GuASCN), guanidine hydrobromide (GuABr), guanidine hydriodate (GuAI)) as passivator is employed to solve this problem. We systematically study the effect of various guanidinium salts on the crystallinity, morphology, and photophysical properties of perovskite films. Guanidine salt as interfacial passivator can decrease interface resistance, reduce carrier non-radiative recombination, and boost carrier extraction. Notably, the GuABr-treated unencapsulated devices can still maintain more than 90 % of their initial PCE after aging for 1600 h at 16-25 °C and 35 %-50 % relative humidity in ambient conditions. This work reveals the significance of counterions in improving the photovoltaic performance and stability of PSCs.

Low-temperature solution-processed Mg: NiOx hole transport layers for formal (n-i-p) perovskite solar cells

NiOx is one of the most promising inorganic hole transport materials for perovskite solar cells. However, lots of fabrication methods refer to NiOx are limited in n-i-p type perovskite solar cells. Because the deposition procedure of NiOx film such as polar solvents and high temperature process is seriously incompatible with perovskite light-absorption underlayers. In this work, highly crystalline NiOx nanocrystals are prepared using solvothermal method under the presence of long-chain oleylamine molecules. The resulted NiOx nanocrystals can be easily dispersed in weak-polar toluene and form films on perovskite layer without annealing procedure. The n-i-p type device with NiOx hole transport layer achieves an efficiency of 10.34%. Later, Mg2+ with different molar ratios are incorporated into the NiOx nanocrystals. It is found that introducing a certain amount of Mg2+ benefits to improve the ratio of Ni3+/Ni2+, thereby changing the work function and increasing the hole conductivity. As a result, the n-i-p type device with Mg-NiOx hole transport layer yields an improved efficiency of 12.41%.

Stabilization of α‐phase FAPbI3 via Buffering Interfacial Region for Efficient p–i–n Perovskite Solar Cells

AbstractFormamidinium lead triiodide (FAPbI3) with an ideal bandgap and good thermal stability has received wide attention and achieved a record efficiency of 26% in n–i–p (regular) perovskite solar cells (PSCs). However, imperfect FAPbI3 formation on the typical hole transport layer (HTL), high interfacial trap‐state density, and unfavorable energy alignment between the HTL and FAPbI3 result in the inferior photovoltaic performance of p–i–n (inverted) PSCs with FAPbI3 absorber. Herein, the α‐phase FAPbI3 is stabilized by constructing a buffer interface region between the NiOx HTL and FAPbI3, which not only diminishes NiOx/FAPbI3 interfacial reactions and defects but also facilitates carrier transport. Upon the construction of a buffer interface region, FAPbI3 inverted PSC exhibits a high‐power conversion efficiency of 23.56% (certified 22.58%) and excellent stability, retaining 90.7% of its initial efficiency after heating at 80 °C for 1000 h and 84.6% of the initial efficiency after operating at the maximum power point under continuous illumination for 1100 h. Besides, as a light‐emitting diode device, the FAPbI3 inverted PSC can be directly lit with an external quantum efficiency of 1.36%. This study provides a unique and efficient strategy to advance the application of α‐phase FAPbI3 in inverted PSCs.

Solution-Processable NiOx:PMMA Hole Transport Layer for Efficient and Stable Inverted Organic Solar Cells.

For organic solar cells (OSCs), nickel oxide (NiOx) is a potential candidate as the hole transport layer (HTL) material. However, due to the interfacial wettability mismatch, developing solution-based fabrication methods of the NiOx HTL is challenging for OSCs with inverted device structures. In this work, by using N, N-dimethylformamide (DMF) to dissolve poly(methyl methacrylate) (PMMA), the polymer is successfully incorporated into the NiOx nanoparticle (NP) dispersions to modify the solution-processable HTL of the inverted OSCs. Benefiting from the improvements of electrical and surface properties, the inverted PM6:Y6 OSCs based on the PMMA-doped NiOx NP HTL achieves an enhanced power conversion efficiency of 15.11% as well as improved performance stability in ambient conditions. The results demonstrated a viable approach to realize efficient and stable inverted OSCs by tuning the solution-processable HTL.

A Top‐Down Strategy for Reforming the Characteristics of NiO Hole Transport Layer in Inverted Perovskite Solar Cells

The hole transport layer (HTL) plays a key role in inverted perovskite solar cells (PSCs), and nickel oxide has been widely adopted for HTL. However, a conventional solution‐processed bottom‐up approach for NiOx (S‐NiO) HTL fabrication shows several drawbacks, such as poor coverage, irregular film thickness, numerous defect sites, and inefficient hole extraction from the perovskite layer. To address these issues, herein, a novel NiOx HTL top‐down synthesis route via electrochemical anodization is developed. The basicity of the electrolyte used in anodization considerably influences electrochemical reactions and results in the structure of the anodized NiOx (A‐NiO). The optimized A‐NiO provides outstanding optoelectrical properties, including uniform film thickness, enhanced transmittance, deep‐lying valance band, low trap density, and better hole extraction ability from the perovskite. Owing to these advantages, the A‐NiO‐based inverted PSC exhibits an improved power conversion efficiency of 21.9% compared with 19.1% for the S‐NiO‐based device. In addition, the A‐NiO device shows a higher inlet and long‐term ambient stability than the S‐NiO device due to the superior hole transfer ability of A‐NiO, which suppresses charge accumulation between NiOx and the perovskite interface.

Boosting efficiency and stability with KBr interface modification for NiOx-based inverted perovskite solar cells

NiOx-based inverted structure perovskite devices possess advantages in the application of single junction and tandem solar cells. However, energy loss and instability originating from interface defects commonly result in inferior device performance. Herein, Potassium Bromide (KBr), as a buffer layer, was inserted between the perovskite and NiOx hole transport layer to modify the interface. The valence band maximum of NiOx improved to −5.37 eV which matches better with perovskite. The lifetime of hot carriers and intrinsic charge recombination revealed by Femtosecond transient absorption spectroscopy (fs-TAS) confirm that KBr modification can facilitate charge separation. Benefiting from the improvement of perovskite quality which results from K+ diffusion and enhanced charge transport, the power conversion efficiency (PCE) of the modified device reaches up to 19.21%, whereas the pristine is 17.56%. Meanwhile, the air stability of the unencapsulated device also improved dramatically, which maintains 80% of its initial PCE after 1100 h high humidity storage. This work unambiguous reveals the mechanism of perovskite/NiOx interface modification and provides a facile and effective strategy for interface optimization.