Hole Transport Material Research Articles

Management of the π-Conjugated System in Carbazole–Diphenylamine Derivative-Based Hole-Transporting Materials for Perovskite Solar Cells: Theoretical Simulation and Experimental Research

Management of the π-Conjugated System in Carbazole–Diphenylamine Derivative-Based Hole-Transporting Materials for Perovskite Solar Cells: Theoretical Simulation and Experimental Research

Unequilibrated Charge Carrier Mobility in Organic Semiconductors Measured Using Injection Metal–Insulator–Semiconductor Charge Extraction by Linearly Increasing Voltage

The charge carrier mobility in tris(4‐carbazoyl‐9‐ylphenyl)amine (TCTA), a host and hole transport material typically used in organic light‐emitting diodes (OLEDs), is measured using charge carrier electrical injection metal–insulator–semiconductor charge extraction by linearly increasing voltage (i‐MIS‐CELIV). By employing the injection current i‐MIS‐CELIV method, charge transport at time scales shorter than the transit times typically observed in standard MIS‐CELIV is measured. The i‐MIS‐CELIV technique enables the experimental measurement of unequilibrated and pretrapped charge carriers. Through a comparison of injection and extraction current transients obtained from i‐MIS‐CELIV and MIS‐CELIV, it is concluded that hole trapping is negligible in evaporated neat films of TCTA within the time‐scales relevant to the operational conditions of optoelectronic devices, such as OLEDs. Furthermore, photocarrier generation in conjunction with i‐MIS‐CELIV (photo‐i‐MIS‐CELIV) to quantify the properties of charge injection from the electrode to the semiconductor of the MIS devices is utilized. Based on the photo‐i‐MIS‐CELIV measurements, it is observed that the contact resistance does not limit the injection current at the TCTA/molybdenum oxide/silver interface. Therefore, when TCTA is employed as the hole transport/electron‐blocking layer in OLEDs, it does not significantly reduce the injection current and remains compatible with the high injection current densities required for efficient OLED operation.

Reactivity Manipulation of Ionic Liquid Based on Alkyl Primary Ammonium: Protonation Control Using 4‐tert‐Butylpyridine Additive for Effective Spontaneous Passivation of Perovskite via Hole Transport Material Deposition

Alkyl‐primary‐ammonium‐based room‐temperature ionic liquids (RTILs) designed to exhibit specific reactivities allowing functions that cannot be achieved by other RTILs have recently emerged. The archetype of the reactive RTILs is n‐octylammonium bis(trifluoromethanesulfonyl)imide (OA‐TFSI), which has promising functions as an additive for hole transport materials (HTMs) in perovskite solar cells (PSCs); the high reactivity of the OA cations on the perovskite surface allows spontaneous perovskite passivation via HTM deposition, effectively improving the photovoltaic (PV) performance. However, although the reactivity manipulation of the reactive RTILs is instrumental for exploiting their potential functions and exploring their application scope, methods for reactivity control have not been developed. Herein, it is proposed that the coaddition of a pyridine derivative (4‐tert‐butylpridine: TBP) can effectively manipulate the reactivity of OA‐TFSI by controlling the protonation between OA and the 2,2′,7,7′‐tetrakis‐(N,N‐di‐4‐methoxyphenylamino)‐9,9′‐spirobifluorene (Spiro‐OMeTAD) HTM. The TBP prevents OA deprotonation presumably via stabilization of the OA cation, thus retaining its ammonium form, which allows efficient spontaneous perovskite passivation, effectively enhancing the PV performance. This reveals the protonation preference in the OA‐TFSI system, which is opposite to that in conventional RTILs. This first proposal of a method in manipulating reactivity of the reactive RTILs will contribute to the development of materials science.

An analysis comparing the performance of lead and tin halides organic Perovskite Solar Cells and numerical simulation with SCAPS

The scientific community focused on finding environmentally safe alternative metal halides to address the instability and toxicity associated with lead perovskite materials. These alternatives are supposed to replace lead halides without altering the distinctive properties of lead perovskite materials. Additionally, they should contribute to producing longer-lasting and stable perovskite in solar cells. This research presents a practical investigation of using tin- and lead-based composites in perovskite iodide solar cells with Titanium dioxide (TiO2) and Copper oxide (CuO) as electron transport materials (ETM) and hole transport materials (HTM), respectively. The performance parameters of the perovskite solar cells (PSCs) are compared with those of lead-based and lead-free PSCs with the same charge transport layers of ETM and HTM, as well as compare the practical results with the software results of Solar Cell Capacitance Simulation (SCAPS) package. In this study, the performance of PSCs with an absorption layer ((CH3NH3PbI3)t/(CH3NH3SnI3)1-t) was examined. The thickness of the perovskite layer is represented by (t), which can take the values(t = 1, 0.5, or 0) μm. The results of the laboratory study were compared to the performance of PSCs based on numerical analysis of SCAPS modeling. PSCs were prepared with a configuration structure (FTO/compact TiO2/(CH3NH3PbI3)t/(CH3NH3SnI3)1-t/CuO/Cu-electrode). A tetragonal phase was obtained for perovskite materials CH3NH3PbI3 and CH3NH3SnI3 with a direct optical energy gap estimated at (1.55 and 1.35) eV, respectively. The l-V curve of the prepared PSCs was studied, and the performance of the solar cells was examined under a light intensity of 100 mW/cm2. The power conversion efficiency, PCE, of the prepared solar cells, was (PCE = 2.9, 3.11, or 0.5) at (t = 1, 0.5, or 0)μm, respectively. A comparative analysis was also performed between the empirical performance of the manufactured PSCs and the theoretical results acquired by the SCAPS package software.

Reducing oxygen vacancies of MoO3 by polyaniline functionalization for stable and efficient inorganic tri-brominated perovskite solar cells

The photovoltaic performance of perovskite solar cells (PSCs) is closely dependent on the efficient carrier extraction and transport at the interface. Here, a polyaniline (PANI) functionalized MoO3 (PANI/MoO3) hole transport material (HTM) is exploited to perfect the interface between the perovskite layer and carbon electrode in all-inorganic CsPbBr3 PSCs. After functionalization with PANI, the p-type behavior and the hole mobility and conductivity of MoO3 are improved by reducing the oxygen vacancies, which boosts the hole extraction and transport, energy level arrangement at the interface of CsPbBr3 perovskite/(PANI/MoO3) HTM. Meanwhile, the PANI/MoO3 with rich C–N and N–H groups introduced by PANI passivates the ions trap states of perovskite films by the C–N⋯Pb2+ (Cs+) Lewis acid-base coordination and the N–H⋯Br− hydrogen bonding, leading to an effective suppression of non-radiative recombination for improved carrier extraction. As a result, the PANI/MoO3 HTMs-based CsPbBr3 PSCs obtain a remarkably increased power conversion efficiency of 10.41 %, in comparison with the efficiency of the original device (6.55 %). In addition, the unencapsulated device with PANI/MoO3 HTMs shows excellent long-term stability with 93.9 % maintenance of the initial efficiency after storing in air with 85 % relative humidity and at 85 °C for 30 days.

Self‐assembling Monolayer‐Assisted Perovskite Growth Enables High‐Performance Solar Cells

Comprehensive SummaryInverted (p‐i‐n) perovskite solar cells (PSCs) are favored by researchers owing to their superior compatibility with flexible substrates and tandem device fabrication. Additionally, the hole transport layer (HTL) serves as a template for perovskite growth, which is critical for enhancing the device performance. However, the current research on how the HTL promotes perovskite crystallization is insufficient. Here, 4PADCB, a self‐assembled monolayer (SAM) hole transport material, was optimized as a superior template for perovskite growth through comparative analysis; accordingly, compact perovskite film with vertical growth was prepared. The better matched energy level alignment between 4PADCB and perovskite suppressed nonradiative recombination at the interface and enabled rapid hole extraction. Moreover, high‐quality perovskite film growth on 4PADCB exhibited lower Young's modulus and less residual stress. By integrating 4PADCB into p‐i‐n PSCs, the optimal device achieved a power conversion efficiency of 24.80%, with an open‐circuit voltage of 1.156 V, thus achieving the best rank among devices without perovskite post‐treatment, additives, dopants, or intermediate layers. Furthermore, the unencapsulated device demonstrated exceptional thermostability and photostability under maximum power point tracking. Thus, this work provides a new understanding for the development of novel SAMs and perovskite growth, and it is expected to further improve device performance.

Glycol Monomethyl Ether-Substituted Carbazolyl Hole-Transporting Material for Stable Inverted Perovskite Solar Cells with Efficiency of 25.52 .

Organic self-assembled molecules (OSAMs) based hole-transporting materials play a pivotal role in achieving highly efficient and stable inverted perovskite solar cells (IPSCs). However, the reported carbazol-based OSAMs have serious drawbacks, such as poor wettability for perovskite solution spreading due to the nonpolar surface, worse matched energy arrangement with perovskite, and limited molecular species, which greatly limit the device performance. To address above problems, a novel OSAM [4-(3,6-glycol monomethyl ether-9H-carbazol-9-yl) butyl]phosphonic acid (GM-4PACz) was synthesized as hole-transporting material by introducing glycol monomethyl ether (GM) side chains at carbazolyl unit. GM groups enhance the surface energy of Indium Tin Oxide (ITO)/SAM substrate to facilitate the nucleation and growth of up perovskite film, suppress cation defects, release the residual stress at SAM/perovskite interface, and evaluate energy level for matching with perovskite. Consequently, the GM-4PACz based IPSC achieves a champion PCE of 25.52 %, a respectable open-circuit voltage (VOC) of 1.21 V, a high stability, possessing 93.29 % and 91.75 % of their initial efficiency after aging in air for 2000 h or tracking at maximum power point for 1000 h, respectively.

Porphyrin-Based Hole-Transporting Materials for Perovskite Solar Cells: Boosting Performance with Smart Synthesis.

Perovskite solar cells (PSCs) are becoming a promising and revolutionary advancement within the photovoltaic field globally. Continuous improvement in efficiency, straightforward processing methods, and use of lightweight and cost-effective materials represent superior features, among other notable aspects. Still, long-term stability and durability are issues to address to facilitate widespread commercial adoption and practical application prospects. Research has focused on overcoming these challenges, and charge transport materials play a critical role in determining charge dynamics, photovoltaic performance, and device stability. Conventional hole-transporting materials (HTMs), spiro-OMeTAD and PTAA, contribute to remarkable power conversion efficiencies owing to high thin-film quality and matched energy alignment. However, they often show a high material cost, low carrier mobility, and poor stability, which greatly limit their practical applications. Now, this review outlines recent advances in synthetic approaches to porphyrin-based HTMs to tune the charge dynamics by optimizing their molecular structures and properties. The main structural features comprise porphyrins of A4-type, trans A2B2-type, and photosynthetic pigment analogues. Strategies include well-established routes to provide the required macrocycles, such as condensation of pyrrole or dipyrromethanes with suitable aldehydes, metalation of the porphyrin inner core, and postfunctionalization of peripheral positions. These functionalizations involve conventional procedures (e.g., halogenation, esterification, transesterification, nucleophilic oxidation, reduction, and nucleophilic substitution) as well as metal-catalyzed ones such as Suzuki-Miyaura, Sonogashira, Buchwald-Hartwig, and Ullmann cross-coupling reactions. As HTMs can also protect the perovskite layer from the external environment, porphyrin structures play a pivotal role in chemical, mechanical, and environmental stability, with their high hydrophobicity ability as the most significant parameter. The impact of porphyrins on the hole hopping of other HTMs while acting as an additive or an interlayer, passivating defects, and improving charge transport is also highlighted to provide real insights into ways to develop efficient and stable porphyrin-based materials for PSCs. This perspective aims to guide the scientific community in the design of new porphyrin molecules to place PSCs as an outperformer in photovoltaic technologies.

Low‐Temperature TiO2 Electron Transporting Layer for Planar Hole Transport Material‐Free Carbon Electrode‐CsFA‐Based Perovskite Solar Cells

Carbon electrode‐based perovskite solar cells (C‐PSCs) without a hole transport material (HTM) are cost‐effective and exhibit impressive long‐term stability. The electron transporting layer (ETL) plays a crucial role in planar CsFA‐based HTM‐free C‐PSCs, serving as both an electron transporter and a hole barrier. Herein, the role of low‐TiO2 morphology and thickness on the performance of CsFA‐based HTM‐free C‐PSCs are addressed. Herein, the devices are fabricated with a simple structure fluorine‐doped tin oxide /TiO2 nanoparticles (TiO2 NPs)/Cs0.17FA0.83Pb(I0.83Br0.17)3/carbon, using low‐temperature processes (≤150 °C) under ambient air conditions. By optimizing TiO2 NP layer thickness via spin‐coating speed adjustments, the ETL's coverage and compactness are improved, enhancing the perovskite film's quality, crystallinity, and grain size. An optimal TiO2 ETL at 1500 rpm yields 10.80% efficiency and demonstrates exceptional stability, maintaining 80% efficiency over 120 days in an air environment without encapsulation. The enhancement in device performance is attributed to improved surface properties of the TiO2 NPs ETL, effectively reducing interfacial charge recombination. This straightforwardly supports the development of sustainable, commercial‐ready CsFA HTM‐free C‐PSCs.

Copper naphthalocyanine-based hole-transport material for high-performance and thermally stable perovskite solar cells

Copper naphthalocyanine-based hole-transport material for high-performance and thermally stable perovskite solar cells

Exploring synthesis, characterization, and computational insights into indacenodithiophene-based hole transporting materials for enhanced perovskite solar cell applications

Utilizing hole-transporting materials (HTMs) to extract and transport holes from perovskite materials to the electrode remains essential in most perovskite solar cell (PSC) architectures. Developing cost-effective and efficient HTMs is essential for advancing PSC technology. We have synthesized a novel HTM, TPA-IDT-TPA, which has an extended fused ring as the core moiety called indacenodithiophene (IDT) and p-methoxy triphenylamine (p-mTPA) as terminal groups. TPA-IDT-TPA exhibits appropriate frontier molecular orbital (FMO) energy levels that match perovskite materials. Density functional theory (DFT) simulations were performed to comprehend the electronic, excited-state, and charge transport properties. The DFT results indicate that the extended π-conjugation, rigidity, and the central core ring of the HTM enhanced the π-π stacking, contributing to efficient charge transport. The PSC constructed with TPA-IDT-TPA achieves a device efficiency of 8.34%, with high values of JSC and VOC, which can be further enhanced through molecular optimization.

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.

Thiocarbonyl-Based Hole Transport Materials with Enhanced Defect Passivation Ability for Efficient and Stable Perovskite Solar Cells.

Organic hole transporting materials (HTMs) are extensively studied in perovskite solar cells (PSCs). The HTMs directly contact the underlying perovskite material, and they play additional roles apart from hole transporting. Developing organic HTMs with defect passivation function has been proved to be an efficient strategy to construct efficient and stable PSCs. In this work, new organic molecules with thiocarbonyl (C═S) and carbonyl (C═O) functional groups are synthesized and applied as HTMs (named FN-S and FN-O). FN-S with C═S can be facilely obtained from FN-O containing C═O. Notably, the C═S in FN-S results in superior defect passivation ability compared to FN-O. Moreover, FN-S exhibits excellent hole extraction/transport capability. Conventional PSCs using FN-S as HTM show an impressive power conversion efficiency (PCE) of 23.25%, with excellent long-term stability and operational stability. This work indicates that simply converting C═O to C═S is an efficient way to improve the device performance by strengthening the defect passivation functionality.

Numerical design of non-toxic high-efficiency tandem solar cell with distinct hole transport materials

The metal-halide perovskite is at the forefront of photovoltaic research and has the potential to combine low manufacturing costs with excellent power conversion efficiency. In this study, a solar cell capacitance simulator was used to analyze the performance of a tandem solar cell in which MASnI3 was used as the lower cell active layer, and NaZn0.7Cu0.3Br3 was used as the upper cell active layer. The primary objective of this research is to search for a device structure with enhanced efficiency. Here, it is evaluated how absorber thickness, temperature, hole transport layer, defect density, and metal work function affect solar cell performance to reach this aim. After looking at the data for several different solar cell configurations, it is seen that indium tin oxide (ITO) / titanium dioxide (TiO2)/sodium zinc copper bromide (NaZn0.7Cu0.3Br3)/ methylammonium tin iodide (MASnI3) / copper oxide (CuO)/gold (Au) offers the best efficiency at 32.58 %, fill factor at 82.19 %, short circuit current density at 34.8389 mA/cm2, and open circuit voltage at 1.1375 Vs. Device simulations showed an optimal MASnI3 absorber thickness of about 1 µm. Finally, the simulation results reveal that the device's efficiency declines when the absorber's defect density and cell operation temperature rise. The device topologies are stable at around 300 Kelvin. Last but not least, any conductive material can be used as an anode if it has a work function that is more than or roughly equivalent to 5.10 eV.

Effects of carbazolyl and diphenylamino substituents bearing methoxy groups on the performance of hole-transporting materials in OLEDs

Newly designed and synthesized derivatives of pentaphenylbenzene with methoxy-substituted carbazolyl or diphenylamino moieties were investigated to estimate their applicability as hole transport materials. Both the compounds exhibit high thermal stability. The intramolecular charge transfer is blocked for the film of the compound containing diphenylamino groups. The intermolecular charge transfer is induced in the film of carbazolyl-containing compound. The derivative of pentaphenylbenzene and diphenylamine exhibits higher hole drift mobility (2.4·10−3 cm2/V·s at the electric field of 5.5·105 V/cm) and by 0.1 eV lower ionization potential than the carbazolyl-containing compound. Both the compounds were utilized as hole-transporting materials in a series of organic light emitting diodes (OLEDs) based on of thermally activated delayed fluorescence. With the maximum values of external quantum efficiency of 25.9 % and power efficiency of 43.4 lm/W, OLEDs containing the layers of the synthesized compounds outperformed the device based on TCTA by 4 %, without the change in spectral properties. Variable angle spectroscopic ellipsometry revealed the moderate average roughness of the films of the compound deposited by the thermal vacuum evaporation technique with an arithmetic mean deviation of not more than 0.8 nm. The prominent hole transport characteristics of the compounds make them good candidates for utilization in optoelectronic devices.

Inorganic hole transport layer for lead free bismuth halide perovskite for photovoltaic device

The finest Hole Transport Layer (HTL) with extraordinary optical and electrical properties are significantly influenced the Power Conversion Efficiency (PCE) of the photovoltaic device. Inorganic hole transport materials exhibit better performance than organic hole transport materials. Herein, we demonstrated that optoelectronic properties of inorganic materials of NiO doped with Cu as Hole Transport Layer (HTL) for Lead free Bismuth halide perovskite solar cell. Solution process method of sol – gel was used to synthesize p-type NiO doped with Cu and yield nano particles of high quality. Cu + doped into Ni2+ sites has improved the crystallization of nanoparticles, carrier mobility and carrier electric properties. Results of the study revealed that the Enhancement of electrical conductivity of about 2 % is obtained for NiO doped with Cu which is ∼1.287 × 10−02 compared to the pristine NiO which is ∼2.655 × 10−03.

Stabilizing Perovskite Solar Cells Based on 2,2′,7,7′‐Tetrakis(N,N‐DI‐P‐Methoxyphenylamine)‐9,9′‐Spirobifluoren with Perfluoropolyethers

Organic–inorganic hybrid perovskites in combination with the hole‐transport material (HTM) 2,2′,7,7′‐tetrakis(N,N‐di‐p‐methoxyphenylamine)‐9,9′‐spirobifluoren (spiro‐OMeTAD) yield impressive power conversion efficiency (PCE) in n–i–p perovskite solar cells (PSC). To ensure sufficient hole extraction from the perovskite absorber to the metal electrode, the lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) doping is considered indispensable to promote spiro‐OMeTAD oxidization and obtain consequently enhanced conductivity. However, LiTFSI‐doped spiro‐OMeTAD usually leads to a reduced stability of PSCs because of the hygroscopic nature of LiTFSI, which further limits its potential commercialization. Herein, a hydrophobic material, namely perfluoropolyethers (PFPEs), is used as surface modifier of doped HTM to improve both efficiency and stability of PSCs. It is revealed that the introduction of PFPE increases the concentration of positive radicals, enhances charge‐carrier transport, and improves stability of PSCs under wetting stress. Moreover, the device based on PFPE achieves a champion PCE of 21.94%. In these findings, valuable insights are provided for the future commercialization of PSCs.

Theoretical investigation of DMPA-containing carbazole-based hole-transport materials for perovskite solar cells

This study mainly focuses on DFT and TD-DFT modelling and extensive analysis of eight carbazole-based molecules (MM, MPM, MP2.5M, MP2.6M, MP3.5M, MPPM, MP2P2M, and MP3P3M) as Hole Transporting Materials in Perovskite Solar cells. These compounds have in common the arm N3,N3,N6,N6-tetrakis(4-methoxyphenyl)-9H-carbazole-3,6-diamine (M) characterized by its strong ability to carry holes, low cost, and good stability. The molecule MM presents two arms without acceptor core, while other compounds present two arms separated by different acceptor cores: phenyl, biphenyl, pyridine or bipyridine. All under-probe compounds were favored candidates for HTMs in perovskite solar cells due to their excellent HOMO delocalization, reduced hole reorganization energies, lower chemical reactivity, longer radiative lifetimes, and spontaneous solvation processes. Flatness proved beneficial when the core consisted of two cycles, particularly for MP2P2M. The results showed that the HOMO levels were primarily influenced by M fragments in most of the molecules, while the LUMO levels were distributed across both the carbazole units and the cores. All molecules exhibited a more stable LUMO compared to that of Spiro-OMETAD, with MP2P2M showing a notably stable level, resulting in a narrower gap. The study found that, except for MP2P2M, these materials did not interfere with the perovskite layer and effectively filled pores. The incorporation of acceptor core groups improved the conjugation backbone and electronic states, significantly enhancing charge transport properties, particularly in molecules with a double ring structure. Furthermore, adding a pyridine center greatly increased solubility, especially in MP3P3M, suggesting that acceptor core inclusion benefits the solubility of the investigated HTMs. The use of two rings core was shown to enhance light harvesting efficiency, boost photocurrent generation, and improve charge transfer performance, particularly in MP2P2M, which is distinguished by its superior flatness, solubility, and charge transfer properties.

Blending Self-Assembled Monolayers for Enhanced Band Alignment and Improved Morphology in p-i-n Perovskite Photodetectors.

Perovskite photodetectors, devices that convert light to electricity, require good extraction and low noise levels to maximize the signal-to-noise ratio. Self-assembling monolayers (SAMs) have been shown to be effective hole transport materials thanks to their atomic layer thickness, transparency, and energetic alignment with the valence band of the perovskite. While efforts are being made to reduce noise levels via the active layer, little has been done to reduce noise via SAM interfacial engineering. Herein, we report hybrid perovskite photodetectors with high detectivity by blending two different SAMs (2-PACz and Me-4PACz). We find that with a 1:1 2-PACz:Me-4PACz ratio (by weight), the devices achieved a low noise of 1 × 10-13 A Hz-1/2, a high responsivity of 0.41 A W-1 at 710 nm, and a specific detectivity of 6.4 × 1011 Jones at 710 nm at -0.5 V, outperforming its two counterparts. In addition to the improved noise levels in these devices, impedance spectroscopy revealed that higher recombination lifetimes of 0.85 μs were achieved for the 1:1 2-PACz:Me-4PACz-based photodetectors, confirming their low defect density.

Evaluating Fluorinated-Aniline Units with Functionalized Spiro[Fluorene-9,9'-Xanthene] as Hole-Transporting Materials in Perovskite Solar Cells and Light-Emitting Diodes.

In the field of perovskite optoelectronics, developing hole-transporting materials (HTMs) on the spiro[fluorene-9,9'-xanthene] (SFX) platform is one of the current research focuses. The SFX inherits the merits of spirobifluorene in terms of the configuration and property, but it is more easily derivatized and regulated by virtue of its binary structure. In this work, we design and synthesize four isomeric SFX-based HTMs, namely m-SFX-mF, p-SFX-mF, m-SFX-oF, and p-SFX-oF, through varying the positions of fluorination on the peripheral aniline units and their substitutions on the SFX core, and the optoelectronic performance of the resulting HTMs is evaluated in both perovskite solar cells (PSCs) and light-emitting diodes (PeLEDs) by the vacuum thermal evaporating hole-transporting layers (HTLs). The HTM p-SFX-oF exhibits an improved power conversion efficiency of 15.21% in an inverted PSC using CH3NH3PbI3 as an absorber, benefiting from the deep HOMO level and good HTL/perovskite interface contact. Meanwhile, the HTM m-SFX-mF provides a maximum external quantum efficiency of 3.15% in CsPb(Br/Cl)3-based PeLEDs, which is attributed to its perched HOMO level and shrunken band-gap for facilitating charge carrier injection and then exciton combination. Through elucidating the synergistic position effect of fluorination on aniline units and their substitutions on the SFX core, this work lays the foundation for developing low-cost and efficient HTMs in the future.