Organic-Hydrochloride-Modified ZnO Electron Transport Layer for Efficient Defect Passivation and Stress Release in Rigid and Flexible all Inorganic Perovskite Solar Cells.

All inorganic CsPbI2Br perovskite (AIP) has attracted great attention due to its excellent resistance against thermal stress as well as the remarkable capability to deliver high-voltage output. However, CsPbI2Br perovskite solar cells (PeSCs) still encounter critical challenges in attaining both high efficiency and mechanical stability for commercial applications. In this work, formamidine disulfide dihydrochloride (FADD) modified ZnO electron transport layer (ETL) has been developed for fabricating inverted devices on either rigid or flexible substrate. It is found that the FADD modification leads to efficient defects passivation, thereby significantly reducing charge recombination at the AIP/ETL interface. As a result, rigid PeSCs (r-PeSCs) deliver an enhanced efficiency of 16.05% and improved long-term thermal stability. Moreover, the introduced FADD can regulate the Young's modulus (or Derjaguin-Muller-Toporov (DMT) modilus) of ZnO ETL and dissipate stress concentration at the AIP/ETL interface, effectively restraining the crack generation and improving the mechanical stability of PeSCs. The flexible PeSCs (f-PeSCs) exhibit one of the best performances so far reported with excellent stability against 6000 bending cycles at a curvature radius of 5 mm. This work thus provides an effective strategy to simultaneously improve the photovoltaic performance and mechanical stability.

Interface modification for efficient carbon-electrode CsPbI2Br perovskite solar cells using ionic liquid.

All-inorganic CsPbI2Br, as a promising photovoltaic (PV) material, have attracted extensive research attention in society for its outstanding thermal stability and appropriate trade-offs. Carbon-based perovskite solar cells (C-PSCs) without hole transporting layer (HTL) have shown great potential in terms of cost-effectiveness and stability. However, the inevitable defects on the surface of CsPbI2Br films severely hampers the development of high-efficiency CsPbI2Br C-PSCs. Surface engineering has emerged an effective approach to overcome this challenge. Herein, 1-decyl-3-methylimidazolium tetrafluoroborate (DMTT) ionic liquid was introduced between CsPbI2Br and carbon electrode to reduce non-recombination of charges, decrease defect states, minimize the energy-level mismatch, and greatly enhance the device stability. As a result, the HTL-free CsPbI2Br C-PSCs combined with DMTT as an interface modification achieved a higher power conversion efficiency (PCE) of 12.47% than that of the control devices with a PCE of 11.32%. Furthermore, without any encapsulation, the DMTT-optimized C-PSC remained approximately 84% of its initial PCE after over 700 h under room temperature and 25% relative humidity (RH) conditions. Additionally, when exposed to a temperature of 65 °C for over 400 h, the device still retained 74% of the initial PCE, demonstrating its thermal stability.

Small Molecules Functionalized Zinc Oxide Interlayers for High Performance Low-Temperature Carbon-Based CsPbI2 Br Perovskite Solar Cells.

The charge recombination resulting from bulk defects and interfacial energy level mismatch hinders the improvement of the power conversion efficiency (PCE) and stability of carbon-based inorganic perovskite solar cells (C-IPSCs). Herein, a series of small molecules including ethylenediaminetetraacetic acid (EDTA) and its derivatives (EDTA-Na and EDTA-K) are studied to functionalize the zinc oxide (ZnO) interlayers at the SnO2 /CsPbI2 Br buried interface to boost the photovoltaic performance of low-temperature C-IPSCs. This strategy can simultaneously passivate defects in ZnO and perovskite films, adjust interfacial energy level alignment, and release interfacial tensile stress, thereby improving interfacial contact, inhibiting ion migration, alleviating charge recombination, and promoting electron transport. As a result, a maximum PCE of 13.94% with a negligible hysteresis effect is obtained, which is one of the best results reported for low-temperature CsPbI2 Br C-IPSCs so far. Moreover, the optimized devices without encapsulation demonstrate greatly improved operational stability.

High-Efficiency Carbon-based CsPbI2 Br Perovskite Solar Cells from Dual Direction Thermal Diffusion Treatment with Cadmium Halides.

In recent years, carbon-based CsPbI2 Br perovskite solar cells (PSCs) have attracted more attention due to their low cost and good stability. However, the power conversion efficiency (PCE) of carbon-based CsPbI2 Br PSCs is still no more than 16%, because of the defects in CsPbI2 Br or at the interface with the electron transport layer (ETL), as well as the energy level mismatch, which lead to the loss of energy, thus limiting PCE values. Herein, a series of cadmium halides are introduced, including CdCl2 , CdBr2 and CdI2 for dual direction thermal diffusion treatment. Some Cd2+ ions thermally diffuse downward to passivate the defects inside or on the surface of SnO2 ETL. Meanwhile, the energy level structure of SnO2 ETL is adjusted, which is in favor of the transfer of electron carriers and blocking holes. On the other hand, part of Cd2+ and Cl- ions thermally diffuse upward into the CsPbI2 Br lattice to passivate crystal defects. Through dual direction thermal diffusion treatment by CdCl2 , CdI2 and CdBr2 , the performance of devices has been significantly improved, and their PCE has been increased from 13.01% of the original device to 14.47%, 14.31%, and 13.46%, respectively. According to existing reports, 14.47% is one of the highest PCE of carbon-based CsPbI2 Br PSCs with SnO2 ETLs.

p-Type Carbon Dots for Effective Surface Optimization for Near-Record-Efficiency CsPbI2 Br Solar Cells.

Interface modification to minimize charge recombination and trapping for efficient charge transport is crucial for the performance of perovskite solar cells (PSCs). Herein, functionalized p-type blue carbon dots (B-CDs) are ventured as an interface passivation layer to enhance the efficiency and long-term stability of all-inorganic CsPbI2 Br PSCs. It is found that first the blue carbon dots with abundant NH, CN, CO, and CO functional groups effectively passivate defects by reacting with I- and Pb2+ ions in the perovskite through hydrogen and coordinative bonds. Second, the p-type B-CDs modifiers form a P-N junction with the n-type perovskite to provide efficient pathways for hole transfer and electron blocking. Third, the B-CDs increase the hydrophobicity of the perovskite film to improve the stability of CsPbI2 Br PSCs. With the above advantages, the CsPbI2 Br PSC with B-CDs modification shows an efficiency as high as 16.76%, one of the highest for its type. In addition, the modification renders significant improvement of air and light stability, with 95.33% of the initial PCE retained after storage in the ambient environment for 1000 h. This work demonstrates the great potential of B-CDs application in perovskite-based optoelectronic devices.

Architecturing 1D-2D-3D Multidimensional Coupled CsPbI2 Br Perovskites toward Highly Effective and Stable Solar Cells.

Despite the rapid development of CsPbIx Br3- x (0 ≤ x ≤ 3) inorganic perovskite solar cells, associated with their superior thermal stability, their low moisture stability limits their commercial deployment. In this study, 1D-2D-3D multidimensional coupled perovskites are prepared by means of an in situ self-integration approach. This pioneering method allows incorporating thus far unreported 1D-Tpy2 Pb3 I6 and 2D-TpyPb3 I6 (Tpy; terpyridine) perovskites. Heterojunction perovskites demonstrate superior stability against water in comparison with control 3D CsPbI2 Br, which is related to the hydrophobicity of low-dimension (LD) perovskites. Remarkably, the spontaneous involvement of LD perovskites can adjust/reconstruct the interfacial structure. This modification allows releasing the residual strain, establishing effective charge transfer channels that increase the carrier transport ability. Accordingly, 1D-2D-3D hybrid CsPbI2 Br perovskite solar cells demonstrate a stabilized power conversion efficiency as high as 16.1%, which represents a very significant improvement, by a factor of 43%, with respect to control 3D CsPbI2 Br perovskite solar cell. Equally importantly, the multidimensional coupled perovskite solar cells exhibit extraordinary stability, well above 1000 h in ambient atmosphere.

Ambient Air Temperature Assisted Crystallization for Inorganic CsPbI2Br Perovskite Solar Cells.

Inorganic cesium lead halide perovskites, as alternative light absorbers for organic-inorganic hybrid perovskite solar cells, have attracted more and more attention due to their superb thermal stability for photovoltaic applications. However, the humid air instability of CsPbI2Br perovskite solar cells (PSCs) hinders their further development. The optoelectronic properties of CsPbI2Br films are closely related to the quality of films, so preparing high-quality perovskite films is crucial for fabricating high-performance PSCs. For the first time, we demonstrate that the regulation of ambient temperature of the dry air in the glovebox is able to control the growth of CsPbI2Br crystals and further optimize the morphology of CsPbI2Br film. Through controlling the ambient air temperature assisted crystallization, high-quality CsPbI2Br films are obtained, with advantages such as larger crystalline grains, negligible crystal boundaries, absence of pinholes, lower defect density, and faster carrier mobility. Accordingly, the PSCs based on as-prepared CsPbI2Br film achieve a power conversion efficiency of 15.5% (the maximum stabilized power output of 15.02%). Moreover, the optimized CsPbI2Br films show excellent robustness against moisture and oxygen and maintain the photovoltaic dark phase after 3 h aging in an air atmosphere at room temperature and 35% relative humidity (R.H.). In comparison, the pristine films are completely converted to the yellow phase in 1.5 h.

Europium and Acetate Co-doping Strategy for Developing Stable and Efficient CsPbI2 Br Perovskite Solar Cells.

All-inorganic perovskite solar cells have developed rapidly in the last two years due to their excellent thermal and light stability. However, low efficiency and moisture instability limit their future commercial application. The mixed-halide inorganic CsPbI2 Br perovskite with a suitable bandgap offers a good balance between phase stability and light harvesting. However, high defect density and low carrier lifetime in CsPbI2 Br perovskites limit the open-circuit voltage (Voc < 1.2 V), short-circuit current density (Jsc < 15 mA cm-2 ), and fill factor (FF < 75%) of CsPbI2 Br perovskite solar cells, resulting in an efficiency below 14%. For the first time, a CsPbI2 Br perovskite is doped by Eu(Ac)3 to obtain a high-quality inorganic perovskite film with a low defect density and long carrier lifetime. A high efficiency of 15.25% (average efficiency of 14.88%), a respectable Voc of 1.25 V, a reasonable Jsc of 15.44 mA cm-2 , and a high FF of 79.00% are realized for CsPbI2 Br solar cells. Moreover, the CsPbI2 Br solar cells with Eu(Ac)3 doping demonstrate excellent air stability and maintain more than 80% of their initial power conversion efficiency (PCE) values after aging in air (relative humidity: 35-40%) for 30 days.

In Situ PL Probes the Effect of 2D SnSe Nanosheets on the Crystallization Process of CsPbI2Br Perovskite Solar Cells.

Reducing defects in the active layer is important for improving the crystalline quality of all-inorganic perovskite solar cells (PSCs). Exploring novel additives is one of the most promising approaches to minimize active layer defects. In this work, two-dimensional (2D) SnSe nanosheets with excellent optoelectronic properties are prepared using an ultrasonic exfoliation method. The prepared 2D SnSe nanosheets are introduced into a CsPbI2Br precursor, which reduces the defect formation at grain boundaries and enhances the crystallinity of CsPbI2Br perovskites. We use the in situ photoluminescence (PL) technique to investigate the role of 2D materials in the crystallization process. The results show that SnSe nanosheets primarily shorten the grain boundary merging time and reduce the defect generation during the grain boundary merging stage, thereby regulating the crystallization of perovskite. In addition, SnSe nanosheets passivate uncoordinated Pb atoms at grain boundaries by Se atoms, further reducing the defect density in perovskite. As a result, PSCs exhibit a higher power conversion efficiency (PCE) of 14.24% and a Voc of 1.22 V. This study highlights the role of 2D materials in enhancing the crystalline quality and PCE of PSCs.

Multifunctional Interface Modification Enables Efficient and Stable HTL-Free Carbon-Electroded CsPbI2Br Perovskite Solar Cells.

In recent years, hole transport layer-free all-inorganic CsPbI2Br carbon-electroded perovskite solar cells (C-PSCs) have garnered significant attention due to a trade-off between stability and photovoltaic performance. However, there are inevitably many defects generated at the surfaces or grain boundaries of CsPbI2Br perovskite films, which will serve as carrier non-radiative recombination centers, and CsPbI2Br perovskite films are sensitive to water molecules to degrade, together with energy level mismatch between CsPbI2Br perovskite and carbon electrodes. Herein, 1-benzyl-3-methylimidazolium hexafluorophosphate (1-B-3-MIMPF6), an imidazolium-based ionic liquid simultaneously containing benzene ring and fluorine atoms, was introduced for the modification of the perovskite/carbon interface. The results showed that it could effectively reduce defects, enhance carrier transfer, mitigate carrier non-radiative recombination, facilitate energy alignment, and block moisture intrusion. Therefore, the photovoltaic performance of the modified PSCs with ITO/SnO2/CsPbI2Br/1-B-3-MIMPF6/carbon architecture has been boosted with a champion power conversion efficiency (PCE) of 13.47 %, open circuit voltage of 1.20 V, short circuit current density of 14.69 mA/cm2, and fill factor of 76 %. Moreover, the unencapsulated modified devices exhibited an improved stability and the PCE maintained 78 % of their initial PCE after 24 h storage at room temperature in a 30 %-35 % humidity environment, whereas that of the pristine devices dropped to almost zero.

Simultaneous Defect Passivation and Electric Level Regulation with Rubidium Fluoride for High-Efficiency CsPbI2Br Perovskite Solar Cells.

Due to the good balance of efficiency and stability, CsPbI2Br perovskite solar cells (PSCs) recently have attracted widespread attention. However, the improvement in photovoltaic performance for CsPbI2Br PSCs was mainly limited by massive defects and unmatched energy levels. Surface modification is the most convenient and effective strategy to decrease defect densities of perovskite films. Herein, we deposited rubidium fluoride (RbF) onto the surface of CsPbI2Br perovskite films by spin-coating. The numerous defects could be significantly passivated by RbF, resulting in suppressed nonradiative recombination. Furthermore, the CsPbI2Br perovskite film after RbF treatment exhibits a deeper Fermi level, and an additional built-in electric field forms to promote charge transport. Consequently, the champion device achieves a high efficiency of 10.82% with an improved VOC of 1.14 V, and it also exhibits excellent stability after long-term storage. This work offers a simple and effective approach to enhance the photovoltaic performance and stability of PSCs for broader applications in the future.

Controlled Crystal Growth of All-Inorganic CsPbI2Br via Sequential Vacuum Deposition for Efficient Perovskite Solar Cells.

Vacuum deposition of perovskites is a promising method for scale-up fabrication and uniform film growth. However, improvements in the photovoltaic performance of perovskites are limited by the fabrication of perovskite films, which are not optimized for high device efficiency in the vacuum evaporation process. Herein, we fabricate CsPbI2Br perovskite with high crystallinity and larger grain size by controlling the deposition sequence between PbI2 and CsBr. The nucleation barrier for perovskite formation is significantly lowered by first evaporating CsBr and then PbI2 (CsBr-PbI2), followed by the sequential evaporation of multiple layers. The results show that the reduced Gibbs free energy of CsBr-PbI2, compared with that of PbI2-CsBr, accelerates perovskite formation, resulting in larger grain size and reduced defect density. Furthermore, surface-modified homojunction perovskites are fabricated to efficiently extract charge carriers and enhance the efficiency of perovskite solar cells (PeSCs) by modulating the final PbI2 thickness before thermal annealing. Using these strategies, the best PeSC exhibits a power conversion efficiency of 13.41% for a small area (0.135 cm2), the highest value among sequential thermal deposition inorganic PeSCs, and 11.10% for a large area PeSC (1 cm2). This study presents an effective way to understand the crystal growth of thermally deposited perovskites and improve their performance in optoelectronic devices.

Zirconium Doping to Enable High-Efficiency and Stable CsPbI2Br All-Inorganic Perovskite Solar Cells.

All-inorganic wide-bandgap perovskite CsPbI2Br has attracted much attention because of its inherent thermal stability and ideal bandgap for the front subcell of tandem solar cells (TSCs). However, the low power conversion efficiency (PCE) and poor moisture stability of CsPbI2Br still restrict its future commercialization. Herein, zirconium tetrachloride (ZrCl4) was doped into CsPbI2Br films to modulate the crystal growth and improve the film quality. The partial substitution of the B-site Pb2+ of CsPbI2Br with Zr4+ suppresses the unwanted phase conversion from the crystallized black α-phase to the δ-phase, resulting in improved phase stability. Consequently, the humidity and thermal stability of the film are greatly improved. Additionally, the incorporation of ZrCl4 suppresses nonradiative recombination and forms a matched energy-level alignment with the hole-transport layer (Spiro-OMeTAD). Benefiting from these features, the ZrCl4-doped CsPbI2Br perovskite solar cell (PSC) shows an outstanding efficiency of 16.60% with a high open-circuit voltage of 1.29 V. The unencapsulated devices simultaneously show excellent humidity and thermal stability, retaining over 91% of PCEinitial after 1000 h of aging in ambient air conditions and 92% PCEinitial after 500 h of continuous heating at 85 °C in a nitrogen environment, respectively. Furthermore, ZrCl4-doped CsPbI2Br was employed as the front subcell of perovskite/organic TSCs and achieved a remarkable PCE of 19.42%, showing great potential for highly efficient and stable TSCs.

Preparation of High-Efficiency (>14%) HTL-Free Carbon-Based All-Inorganic Perovskite Solar Cells by Passivation with PABr Derivatives.

Due to the advantages of low cost and good thermal stability, all-inorganic CsPbI2Br carbon-based perovskite solar cells (C-PSCs) without a hole transport layer have been rapidly developed in recent years. While the carbon electrode is in direct contact with the CsPbI2Br film, higher requirements are placed on the defects and energy level arrangement of the CsPbI2Br layer, which leads to the relatively low photoelectric conversion efficiency (PCE) of C-PSCs. Herein, propylamine hydrobromide (PABr) and its derivative 3-bromopropylamine hydrobromide (3Br-PABr) were used to passivate the surface defects of CsPbI2Br C-PSCs for the first time. The results show that passivation molecules are modulated by the substituent effect, leading to a stronger interaction between amino groups and uncoordinated Pb2+ ions, which facilitates a better passivation effect of 3Br-PABr. In addition, 3Br-PABr promotes the gradient arrangement of energy levels while passivating surface defects, which accelerates the rapid extraction of holes. After the passivation by PABr and 3Br-PABr, the PCE of HTL-free CsPbI2Br C-PSCs increased from 12.15% for the control device to 13.15 and 14.04%, respectively, which are among the highest reported values of CsPbI2Br C-PSCs.

Dendrimer Modification Strategy Based on the Understanding of the Photovoltaic Mechanism of a Perovskite Device under Full Sun and Indoor Light.

The wide-band-gap inorganic CsPbI2Br perovskite material provides a highly matched absorption range with the indoor light spectrum and is expected to be used in the fabrication of highly efficient indoor photovoltaic cells (IPVs) and self-powered low-power Internet of Things (IoT) sensors. However, the defects that cause nonradiative recombination and ion migration are assumed to form leakage loss channels, resulting in a severe impact on the open-circuit voltage (VOC) and the fill factor (FF) of IPVs. Herein, we introduce poly(amidoamine) (PAMAM) dendrimers with multiple passivation sites to fully repair the leakage channels in the devices, taking into account the characteristics of IPVs that are extremely sensitive to nonradiative recombination and shunt resistance. The as-optimized IPVs demonstrate a promising PCE of 35.71% under a fluorescent light source (1000 lux), with VOC increased from 0.99 to 1.06 V and FF improved from 75.21 to 84.39%. The present work provides insight into the photovoltaic mechanism of perovskites under full sun and indoor light, which provides guidance for perovskite photovoltaic technology with industrialization prospects.

Role of Dibenzo Crown Additive for Improving the Stability of Inorganic Perovskite Solar Cells.

Photovoltaics are being transformed by perovskite solar cells. The power conversion efficiency of these solar cells has increased significantly, and even higher efficiencies are possible. The scientific community has gained much attention due to perovskites' potential. Herein, the electron-only devices were prepared by spin-coating and introducing the organic molecule dibenzo-18-crown-6 (DC) to CsPbI2Br perovskite precursor solution. The current-voltage (I-V) and J-V curves were measured. The morphologies and elemental composition information of the samples were obtained by SEM, XRD, XPS, Raman, and photoluminescence (PL) spectroscopies. The distinct impact of organic DC molecules on the phase, morphology, and optical properties of perovskite films are examined and interpreted with experimental results. The efficiency of the photovoltaic device in the control group is 9.76%, and the device efficiency gradually increases with the increase of DC concentration. When the concentration is 0.3%, the device efficiency is the best, reaching 11.57%, short-circuit current is 14.01 mA/cm2, the open circuit voltage is 1.19 V, and the fill factor is 0.7. The presence of DC molecules effectively controlled the perovskite crystallization process by inhibiting the in-situ generations of impurity phases and minimizing the defect density of the film.

Notable Performance Enhancement of CsPbI2Br Solar Cells by a Dual-Function Strategy with CsPbBr3 Nanocrystals.

Herein, a dual-function strategy, in which CsPbI2Br is treated by CsPbBr3 nanocrystals (NCs) via addition and surface modification to construct the "electron bridge" and gradient heterojunction, respectively, to notably improve the performance of the CsPbI2Br solar cells, is proposed. The "electron bridge" formed by the CsPbBr3 NCs provides an extra transport channel for the photogenerated electrons in the CsPbI2Br layer, thus facilitating electron transport. Meanwhile, surface modification of CsPbI2Br by the CsPbBr3 NCs forms a gradient heterojunction between the CsPbI2Br layer and the P3HT layer, enhancing hole extraction accordingly. In addition, the CsPbBr3 NC treatment passivates the defects at the bulk and surface of the CsPbI2Br layers, thus suppressing carrier recombination. Thanks to these positive effects of the CsPbBr3 NCs, the demonstration device with a simple configuration of ITO/SnO2/CsPbI2Br/P3HT/Ag achieves a notable power conversion efficiency of 17.03%, which is among the highest efficiencies reported for CsPbI2Br-based solar cells.

Approaching the Fill Factor Limit in Dopant-Free Hole Transporting Layer-Based All-Inorganic Perovskite Solar Cells.

As an important part of perovskite solar cells (PSCs), hole transporting layer (HTL) has a critical impact on the performance and stability of the devices. In an attempt to alleviate the moisture and thermal stability issues from the commonly used HTL Spiro-OMeTAD with dopant, it is urgent to develop novel HTLs with high stability. In this study, a new class of polymers D18 and D18-Cl are applied as undoped HTL for CsPbI2Br-based PSCs. In addition to the excellent hole transporting properties, we unveil that D18 and D18-Cl with larger thermal expansion coefficient than that of CsPbI2Br could impose a compressive stress onto the CsPbI2Br film upon thermal treatment, which could release the residual tensile stress in the film. As a result, the efficiency of CsPbI2Br-based PSCs with D18-Cl as HTL reaches 16.73%, and the fill factor (FF) exceeds 85%, which is one of the highest FF records for the conventional-structured device to date. The devices also show impressive thermal stability with over 80% of the initial PCE retained after 85 °C heating for 1500 h.

One-Step Thermal Gradient- and Antisolvent-Free Crystallization of All-Inorganic Perovskites for Highly Efficient and Thermally Stable Solar Cells.

All-inorganic perovskites have emerged as promising photovoltaic materials due to their superior thermal stability compared to their heat-sensitive hybrid organic-inorganic counterparts. In particular, CsPbI2 Br shows the highest potential for developing thermally-stable perovskite solar cells (PSCs) among all-inorganic compositions. However, controlling the crystallinity and morphology of all-inorganic compositions is a significant challenge. Here, a simple, thermal gradient- and antisolvent-free method is reported to control the crystallization of CsPbI2 Br films. Optical in situ characterization is used to investigate the dynamic film formation during spin-coating and annealing to understand and optimize the evolving film properties. This leads to high-quality perovskite films with micrometer-scale grain sizes with a noteworthy performance of 17% (≈16% stabilized), fill factor (FF) of 80.5%, and open-circuit voltage (VOC ) of 1.27 V. Moreover, excellent phase and thermal stability are demonstrated even after extreme thermal stressing at 300 °C.

Simple-Structured Low-Cost Dopant-Free Hole-Transporting Polymers for High-Stability CsPbI2Br Perovskite Solar Cells.

Among the solution-processed devices, perovskite solar cells (PSCs) exhibit the highest power conversion efficiency (PCE) of over 25%; tremendous efforts are being undertaken to improve their stability. Recently, all-inorganic CsPbI2Br-based PSCs were reported to exhibit a significantly improved device stability, with a promising PCE of up to 16.79%. In this study, we report stable all-inorganic PSCs by incorporating novel dopant-free hole-transporting materials (HTMs). The synthesis strategy of the newly synthesized polymeric HTMs was similar to that of 2,2',7,7'-tetrakis(N,N-di-p-methoxyphenylamine)-9,9'-spirobifluorene (spiro-OMeTAD), with the exception that they were designed to exhibit dopant-free characteristics. In particular, their polymeric backbone structure was significantly simpler than that of spiro-OMeTADs, and they were easily synthesized in two steps from commercially available chemicals, with an overall yield of ∼50%. The cost of synthesis at the laboratory scale was calculated to be at least 2.4 times cheaper than that of spiro-OMeTADs. The PCE of dopant-free HTM-based PSCs was 11.01%, which is 1.5 times higher than that of the dopant-free spiro-OMeTAD-based devices (7.52%) and comparable to that of the doped spiro-OMeTAD-based devices (12.22%). Notably, the stability of the device based on our dopant-free HTM to atmospheric oxygen and moisture as well as heat and light irradiation was superior to that of devices based on doped and dopant-free spiro-OMeTAD HTMs. On consideration of the synthesis cost, device efficiency, and device stability, our dopant-free HTM is highly promising for all-inorganic PSCs.