Organic Hole Transport Materials Research Articles

Dopant-Free Hole Transport Material Based on Non-Covalent Interaction for Efficient Perovskite Solar Cells.

Hole transport materials (HTMs) have a critical impact on the performance of perovskite solar cells (PSCs). Especially, the dopant-free HTMs could avoid the usage of hygroscopic dopants and reduce costs, which are important for device stability. Most of the current organic dopant-free HTMs are polycyclic aromatic hydrocarbons-based planar conjugated structures. Yet, the synthesis of conjugated fused heterocycles is often complicated. In this work, intramolecular non-covalent interaction is introduced to construct two organic HTMs (DCT and DTC), which can be facilely obtained through simple reactions. Compared to DTC with hexyl chain on the central benzene ring, DCT with hexyloxy chains shows better planarity in the core structure, as a result of the intramolecular non-covalent interactions between oxygen on hexyloxy and sulfur atom on the adjacent thiophene, as reflected from its single crystal structure. Moreover, DCT in a pristine state shows a decent hole mobility comparable to the doped Spiro-OMeTAD. Ultimately, conventional devices using dopant-free DCT as HTM show a high efficiency of 22.50%, with excellent long-term stability, and light and thermal stability. The results show that the noncovalent interaction is a useful and simple design strategy for dopant-free HTMs, that can effectively improve the efficiency and stability of PSCs.

Understanding the Role of Organic Hole Transport Layers on Pinhole Blocking and Performance Improvement in Sb2Se3 Solar Cells

AbstractSb2Se3 is an emerging semiconductor which has shown promise for low‐cost photovoltaic applications. After successive record‐efficiencies using a range of device structures, spiro‐OMeTAD has emerged as the default hole transport material (HTM), however, the function of HTM layers remains poorly understood. Here, thin‐film Sb2Se3 solar cells are fabricated with which three organic HTM layers ‐ namely P3HT, PCDTBT, and spiro‐OMeTAD are investigated. By comparing these against one another, and to a reference device, their role in the device stack are clarified. These organic HTM layers are found to serve a dual purpose, increasing both the average and peak efficiency by simultaneously blocking pinholes and improving the band alignment at the back contact, with marginal differences in performance between the different HTMs. This produced a champion device of 7.44% using P3HT, resulting from an improvement in all performance parameters. A more complex processing route, run‐to‐run variability, and lower overall device performance compared to the other organics challenge the assumption that spiro‐OMeTAD is the optimal HTM for Sb2Se3 devices. A Schottky barrier at the Au‐Sb2Se3 contact despite the deep work function of gold implies Fermi level pinning due to a defective interface, which each of the organic HTMs are equally capable of alleviating.

Synthesis and scalable process for fabrication of Perovskite Solar Cells using organic and inorganic hole transport materials

The Organic Inorganic Lead Iodide perovskite material has emerged as a pioneer in being an active material for third-generation solar cells. Apart from the synthesis, the scalable mechanism which is being used for the deposition process, greatly influences the performance of the cell owing to its impact on the morphology, uniform thickness, and interface between two functional layers. This study briefly discusses the various deposition processes involved in assembling the layers of perovskite solar cells (PSC). Hole transport materials (HTM) are a crucial part of the PSC providing efficient transport of the charge carriers. However, the effect of organic and inorganic HTMs is highly pronounced in the PSCs. This study also discusses the effect of organic and inorganic HTM on the stability and efficiency of the sandwich-structured PSC.

Dibenzothiophene S, S-Dioxide-Containing Dipolar Molecules As Efficient Hole-Transport Materials for p-i-n Perovskite Solar Cells.

Organic-inorganic hybrid perovskite solar cells (OIH-PSCs) have developed rapidly in the past decade, and the commercialization of OIH-PSCs demands low-cost hole-transport materials (HTMs) with high performance and stability. The present study synthesized two organic HTMs containing dibenzothiophene S-dioxide as the acceptor unit and triphenylamine as the donor (denoted by TPAF-SO2 and TPA-SO2). In TPAF-SO2, the methoxy group and adjacent fluorine atom were introduced to decrease the highest occupied molecular orbital energy level. In TPA-SO2, the methyl sulfide group is the end group that can passivate the lead ion. TPAF-SO2 and TPA-SO2 exhibit hole-transport mobilities as high as 1.12 × 10-3 and 2.31 × 10-3 cm2 v-1 s-1, respectively, and strongly passivate Pb vacancies. Compared with TPAF-SO2, TPA-SO2 is more suitable for the growth of perovskite crystals. The perovskite grown on the latter has a lower trap density and higher carrier mobility; thus, both the nonradiative recombination and the charge-transport loss are decreased. The OIH-PSC based on TPA-SO2 as the HTM achieved a power conversion efficiency (PCE) as high as 22.08%, whereas the device based on TPAF-SO2 achieved a PCE of only 18.42%. In addition, the unencapsulated device based on TPA-SO2 can maintain 85% of the initial PCE after being stored in N2 for 1200 h, whereas the device based on TPAF-SO2 decayed rapidly to zero in 800 h under the same conditions.

Enhancing perovskite solar cells performance through tailored design: pyridine-functionalized phenothiazine derivatives with modified end-capped acceptor moieties

Abstract Future energy resources are being developed using clean and renewable energies since these sources offer environmentally friendly and sustainable choices to traditional sources like fossil fuels. Among various renewable energy sources, solar energy is becoming increasingly efficient with advancements in organic photovoltaic systems. Organic semiconductor materials, which require high electron affinity and possess desirable optical and electronic properties, are crucial for these systems. Researchers are constantly trying to increase the role of photovoltaic materials in optoelectronic applications. With current energy demands, there is a shift from traditional solar cells to perovskite photovoltaic materials due to their significant contributions to renewable energy. Therefore, we have designed a new stream of donor- π -acceptor (D- π -A) type pyridine functionalized phenothiazine derivates-based donor materials, resulting in nine fabricated HTMs (PT1-PT9), by substituting the terminals with thiophene and acceptors moieties respectively to enhance the photovoltaic properties of perovskite solar cells (PSCs). All newly proposed materials were computationally examined to estimate their optoelectronics, geometrical, and photovoltaic properties using quantum chemical approach, and then compared to the reference. For organic hole-transporting materials, a heterocyclic phenothiazine core (PTZ) has been proven effective as it has feasible structure modifications, excellent electron-donating properties, and straightforward synthesis. The study of electronic parameters (density of state, frontier molecular orbitals, and electrostatic potential ESP), optical properties (light harvesting efficiency, absorption maxima, dipole moment, and first excitation energies) and charge transfer characteristics (electron–hole overlap, transition density matrix) of designed materials revealed that there is an increase in absorption range under the influence of terminal acceptor groups, with lowering the bandgap values compared to the reference. A density of state (DOS) graph and HOMO–LUMO schema are evidence of the electron-withdrawing effect of acceptor moieties. Transition density matrix (TDM) analysis proves reliable charger transfer in designed molecules. Reorganization energy values for designed molecules are lower than the reference making charge transfer carriers more efficient. Additionally, solvation-free energy values (−17.28 to −33.19 Kcalmol−1) and higher dipole moments suggest better surface-wetting and solubility properties. In general, the fabricated materials have exceptional charge mobilities with higher absorption and reduced band gap values that make them suitable and stable candidates for photovoltaic devices.

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.

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.

Trade-off effect of hydrogen-bonded dopant-free hole transport materials on performance of inverted perovskite solar cells

Benefiting from their ordered orientation and superior stability compared to traditional conjugated materials, hydrogen bonding (HB)-induced H-aggregates in organic small molecule hole-transport materials (HTMs) hold a big potential for high-performance inverted perovskite solar cells (IPSCs). However, H-aggregates can also lead to excessive face-aggregation by forming the gaps between aggregates, which is in turn unfavorable for charge mobility and thus for the overall device performance. Herein, we design and synthesize a new set of HB-containing triphenylamine-based small molecules to tailor the degree of H-aggregation, namely O1 (without HB), O2 (unilateral HB unit), and O3 (bilateral HB units). These HTMs make a clear trade-off effect on the charge mobility within the HTM and the interfacial properties of perovskite and HTM. Although the interfacial hole extraction process is promoted upon the HB-functionalized interface, the best performance of IPSCs is still achieved by O1 HTM, which is mainly influenced by the higher hole mobility without HB-induced H-aggregates. Nevertheless, the photo stability of as-fabricated devices is effectively improved upon the HB passivation effect on the interface of HTM (O2 or O3) and perovskite, as well as the better quality of atop perovskite layers with less grain boundary compared to the reference case (O1).

Unveiling the Role of BODIPY Dyes as Small‐Molecule Hole Transport Material in Inverted Planar Perovskite Solar Cells

Perovskite solar cells (PSCs) have become a research hotspot since their dramatic increase in power conversion efficiency (PCE), surpassing 26% due to advances in cell engineering and interfacial layers. Within the last factor, hole transporting materials play a crucial role in enhancing device performance and stability. Among several molecular building blocks, BODIPYs are attractive for the design of novel hole transporting material (HTMs) due to their outstanding photophysical and charge transport properties easily tuned by synthetic modifications. Herein, the synthesis of five new BODIPY‐based HTMs PyBDP 1–5 are reported, functionalized at the meso‐ and α‐ positions with pyrenyl and arylamino units, respectively. The resulting compounds exhibit broad absorption in the visible region, remarkable thermal stability, narrow bandgaps, suitable energy levels, and good hole extraction capability, as subtracted from experimental and computational characterizations. The performance of the BODIPY derivatives as HTMs is evaluated in planar inverted (p‐i‐n) PSCs and compared to commonly used PTAA, resulting in highly efficient systems, reaching PCEs very close to that obtained with the reference polymer (21.51%). The incorporation of these BODIPY‐based HTMs result in an outstanding PCE of 20.37% for devices including PyBDP‐1 and 19.97% for devises containing PyBDP‐3, thus demonstrating that BODIPY derivatives are a promising alternative to obtain simple and efficient organic HTMs.

Stable and efficient perovskite solar cells based on tert-butyl peroxy-2-ethylhexanoate modified hole transport layer

Nowadays, perovskite solar cells (PSCs) have gained significant attention as one of the most promising new energy technologies. However, the application of spiro-OMeTAD, a highly efficient organic hole transport material (HTM) in PSCs, is limited due to its inherent weaknesses in conductivity and hole mobility. Here, a free radical initiator, tert-butyl peroxy-2-ethylhexanoate (TBPEH) is introduced to induce the rapid and controllable oxidation of Spiro. TBPEH-modified hole transport layer (HTL) produces more free radical cations, increasing carrier mobility and electrical conductivity. A smoother surface of the modified HTL improves the charge transport efficiency. Additionally, trap-state density and defect-induced nonradiative recombination of TBPEH-modified device are decreased. In addition, better energy level matching between the HTL and perovskite layer enables more efficient hole transport. Consequently, the PSC doped with TBPEH achieves a champion power conversion efficiency (PCE) of 24.33 %, surpassing the PCE of 21.72 % obtained from the pristine device. Furthermore, the TBPEH-modified devices show better stability. Storing in the atmosphere at 30 % relative humidity for 42 days, the TBPEH-modified device maintains 90.8 % of its highest efficiency, compared to the 73.8 % of the pristine one.

Durable Perovskite Solar Cells with 24.5% Average Efficiency: The Role of Rigid Conjugated Core in Molecular Semiconductors.

Efficient and robust n-i-p perovskite solar cells necessitate superior organic hole-transport materials with both mechanical and electronic prowess. Deciphering the structure-property relationship of these materials is crucial for practical perovskite solar cell applications. Through direct arylation, two high glass transition temperature molecular semiconductors, DBC-ETPA (202°C) and TPE-ETPA (180°C) are synthesized, using dibenzo[g,p]chrysene (DBC) and 1,1,2,2-tetraphenylethene (TPE) tetrabromides with triphenylene-ethylenedioxythiophene-dimethoxytriphenylamine (ETPA). In comparison to spiro-OMeTAD, both semiconductors exhibit shallower HOMO energy levels, resulting in increased hole densities (generated by air oxidation doping) and accelerated hole extraction from photoexcited perovskite. Experimental and theoretical studies highlight the more rigid DBC core, enhancing hole mobility due to reduced reorganization energy and lower energy disorder. Importantly, DBC-ETPA possesses a higher cohesive energy density, leading to lower ion diffusion coefficients and higher Young's moduli. Leveraging these attributes, DBC-ETPA is employed as the primary hole-transport layer component, yielding perovskite solar cells with an average efficiency of 24.5%, surpassing spiro-OMeTAD reference cells (24.0%). Furthermore, DBC-ETPA-based cells exhibit superior operational stability and 85°C thermal storage stability.

Dual‐Strategy Tailoring Molecular Structures of Dopant‐Free Hole Transport Materials for Efficient and Stable Perovskite Solar Cells

AbstractDopant‐free hole transport materials (HTMs) are ideal materials for highly efficient and stable n‐i‐p perovskite solar cells (PSCs), but most current design strategies for tailoring the molecular structures of HTMs are limited to single strategy. Herein, four HTMs based on dithienothiophenepyrrole (DTTP) core are devised through dual‐strategy methods combining conjugate engineering and side chain engineering. DTTP‐ThSO with ester alkyl chain that can form six‐membered ring by the S⋅⋅⋅O noncovalent conformation lock with thiophene in the backbone shows good planarity, high‐quality film, matching energy level and high hole mobility, as well as strong defect passivation ability. Consequently, a remarkable power conversion efficiency (PCE) of 23.3 % with a nice long‐term stability is achieved by dopant‐free DTTP‐ThSO‐based PSCs, representing one of the highest values for un‐doped organic HTMs based PSCs. Especially, the fill factor (FF) of 82.3 % is the highest value for dopant‐free small molecular HTMs‐based n‐i‐p PSCs to date. Moreover, DTTP‐ThSO‐based devices have achieved an excellent PCE of 20.9 % in large‐area (1.01 cm2) devices. This work clearly elucidates the structure‐performance relationships of HTMs and offers a practical dual‐strategy approach to designing dopant‐free HTMs for high‐performance PSCs.

Dual-Strategy Tailoring Molecular Structures of Dopant-Free Hole Transport Materials for Efficient and Stable Perovskite Solar Cells.

Dopant-free hole transport materials (HTMs) are ideal materials for highly efficient and stable n-i-p perovskite solar cells (PSCs), but most current design strategies for tailoring the molecular structures of HTMs are limited to single strategy. Herein, four HTMs based on dithienothiophenepyrrole (DTTP) core are devised through dual-strategy methods combining conjugate engineering and side chain engineering. DTTP-ThSO with ester alkyl chain that can form six-membered ring by the S⋅⋅⋅O noncovalent conformation lock with thiophene in the backbone shows good planarity, high-quality film, matching energy level and high hole mobility, as well as strong defect passivation ability. Consequently, a remarkable power conversion efficiency (PCE) of 23.3 % with a nice long-term stability is achieved by dopant-free DTTP-ThSO-based PSCs, representing one of the highest values for un-doped organic HTMs based PSCs. Especially, the fill factor (FF) of 82.3 % is the highest value for dopant-free small molecular HTMs-based n-i-p PSCs to date. Moreover, DTTP-ThSO-based devices have achieved an excellent PCE of 20.9 % in large-area (1.01 cm2) devices. This work clearly elucidates the structure-performance relationships of HTMs and offers a practical dual-strategy approach to designing dopant-free HTMs for high-performance PSCs.

Low-cost dopant-free fluoranthene-based branched hole transporting materials for efficient and stable n-i-p perovskite solar cells

It has been widely recognized that hole transporting materials (HTMs) play a key role in the rapid progress of perovskite solar cells (PVSCs). However, common organic HTMs such as spiro-OMeTAD not only suffer from high synthetic costs, but also usually require the additional chemical doping process to improve their hole transport ability, which unfortunately induces the terrible stability issue. Therefore, it is urgent to develop low-cost dopant-free HTMs for efficient and stable PVSCs. In this work, we have successfully developed a new class of efficient dopant-free fluoranthene-based HTMs (TPF1–5) with quite low lab synthetic costs by combining donor-acceptor and branched structure designs. The detailed structure-property study revealed that tuning the twisted arms at different substitution sites would regulate the intermolecular interactions and film-forming ability, thereby significantly affecting the performance of the HTMs. By applying these HTMs in conventional PVSCs, the dopant-free TPF1-based devices not only achieved the best efficiency of 21.76%, which is comparable to that of the doped spiro-OMeTAD control devices, but also showed much better operational stability, which maintained over 87% of the initial efficiency under maximum power point tracking after 1038 h.

Organic-inorganic hybrid material for hole transport in inverted perovskite solar cells.

Hole mobility is critical to the power conversion efficiencies of perovskite solar cells (PSCs). Organic small-molecule hole-transporting materials (HTMs) have attracted considerable interest in PSCs due to their structural flexibility and operational durability, but they suffer from modest hole mobility. On the other hand, inorganic HTMs with good hole mobility are inflexible in structural variation and exhibit unsatisfactory cell efficiency. In this study, a ligand BT28 and its zinc-based coordination complex BTZ30 were synthesized, characterized, and investigated as HTMs for PSC applications. The mixed-halide perovskites can be grown uniformly with large crystalline grains on both HTMs, which exhibit similar optical and electrochemical properties. However, it was discovered that the BTZ30-based solar cell exhibited an open-circuit voltage of 1.0817 V and a high short-circuit current density of 23.1392 mA cm-2 with a champion power conversion efficiency of close to 20 %. The performance difference between the two HTMs can be attributed to the difference in their hole mobilities, which is 63.31 % higher for BTZ30 than BT28. The comparison of non-metal and metal HTMs revealed the importance of considering hybrid structures to overcome some shortcomings associated with organic and inorganic HTMs and achieve high-performance PSCs.

Theoretical investigation of triphenylamine/anthradithiophene based systems as potential organic hole transport materials for perovskite solar cells

Hole transport materials (HTMs) are important constituents in perovskite solar cell fabrication. In this work structure property relationship of five different HTMs based on triphenylamine/anthradithiophene systems are investigated using DFT method. The orientation of the attachment of the thiophene rings on the anthracene core of anthradithiophene system has significant effect on the electronic and optical properties of the HTMs. The results are compared with the well-known HTMs. The predicted hole mobility of the molecules are found to be similar order of magnitude as that of spiro-OMeTAD. Thus, these HTMs can be potential replacements for spiro-OMeTAD in perovskite solar cell applications.

Metal complex as p-type dopant-based organic spiro-OMeTAD hole-transporting material for free-Li-TFSI perovskite solar cells.

Lithium bis(fluorosulfonyl)imide (Li-TFSI) is an efficient p-dopant that has been used to enhance the conductivity of perovskite solar cells (PSCs). However, the performance of the corresponding devices is still not satisfactory due to the impact of Li-TFSI on the fill factor and the short-circuit current density of these PSCs. Herein, a new Mn complex [(Mn(Me-tpen)(ClO4)2-)]2+ was introduced as a p-type dopant into spiro-OMeTAD and was successfully applied as a hole transport material (HTM) for PSCs. Analytical studies used for device characterization included scanning electron microscopy, UV-Vis spectroscopy, current-voltage (IV) characteristics, incident photon to current efficiency, power conversion efficiency (PCE), and electrochemical impedance spectroscopy. The UV-Vis spectra displayed oxidation in the HTM by the addition of a dopant. Moreover, the movement of electrons from the higher orbital of the spiro-OMeTAD to the dopant stimulates the generation of the hole carriers in the HTM, enhancing its conductivity with outstanding long-term stability under mild conditions in a humid (RH ∼ 30%) environment. The incorporation of the Mn complex into the composite improved the material's properties and the stability of the fabricated devices. The Mn complex as a p-type dopant for spiro-OMeTAD exhibits a perceptible PCE of 16.39% with an enhanced conductivity of 98.13%. This finding may pave a rational way for developing efficient and stable PSCs in real environments.

Complex Metal Oxides as Emerging Inorganic Hole-Transporting Materials for Perovskite Solar Cells.

Perovskite solar cells (PSCs) have achieved revolutionary progress during the past decades with a rapidly boosting rate in power conversion efficiencies from 3.8% to 26.1%. However, high-efficiency PSCs with organic hole-transporting materials (HTMs) suffer from inferior long-term stability and high costs. The replacement of organic HTMs with inorganic counterparts such as metal oxides can solve the above-mentioned problems to realize highly robust and cost-effective PSCs. Nevertheless, the widely used simple metal oxide-based HTMs are limited by the low conductivity and poor light transmittance due to the fixed atomic environment. As an emerging family of inorganic HTMs, complex metal oxides with superior structural/compositional flexibility have attracted rapidly increasing interest recently, showing superior carrier conductivity/mobility and superb light transmittance. Herein, the recent advancements in the design and development of complex metal oxide-based HTMs for high-performance PSCs are summarized by emphasizing the superiority of complex metal oxides as HTMs over simple metal oxide-based counterparts. Consequently, several distinct strategies for the design of complex metal oxide-based HTMs are proposed. Last, the future directions and remaining challenges of inorganic complex metal oxide-based HTMs for PSCs are also presented. This review aims to provide valuable guidelines for the further advancements of robust, high-efficiency, and low-cost PSCs.

Cross-linkable fluorene-based hole transporting materials for perovskite solar cells

Cross-linkable hole transporting materials (HTMs) based on fluorene core containing vinyl groups were synthesized and analyzed. It has been demonstrated that these HTMs are cross-linkable at temperatures above 200 °C and they are thermally stable at up to 400 °C. Cross-linking has little effect on energy level (HOMO) and causes only slight changes in the hole drift mobility values at room temperature, due to changes in spatial and energetic disorder. While employing cross-linked fluorene-diphenylamine derivative (V1145) as an HTM layer between perovskite and indium-tin oxide (ITO) in inverted perovskite solar cells (PSCs), the power conversion efficiency (PCE) of the cell was 11.42% (under AM 1.5G 100 mW cm−2 illumination), demonstrating the potential of the presented class of dopant-free organic HTMs.