JIALINGBO

Aiming at improving the performance of tin perovskite solar cells, this study analyzes the Sn²⁺ oxidation process in the precursor solution and proposes a source-regulating strategy to prepare high-quality perovskite films with low Sn⁴⁺ defect densities. A device with high certified efficiency and excellent long-term stability is obtained.

Abstract

Tin-based halide perovskites have attracted great attention in the perovskite solar cells (PSCs) community with their suitable band gaps, excellent optoelectronic properties, and non-toxicity. However, because of their poor chemical stability, it is challenging to fabricate highly stable and efficient tin PSCs (TPSCs). In this study, the origin of the Sn²⁺ oxidation ahead of film formation is concentrated on, and it is found that the ionization of SnI₂ in precursor plays a decisive role. Accordingly, SnI₂ dissociation and the subsequent Sn²⁺ oxidation can be restricted in precursor by employing reductive complexes as additives. This dual-functional source-regulating strategy effectively helps prepare high-quality perovskite films with low Sn⁴⁺ defect densities. As a result, the unencapsulated TPSCs show a considerable power-conversion efficiency of 10.03% (certified 9.38%) and maintain 90% of its initial efficiency after 1000 h of light aging testing.

Ethylenediamine (EDA) coating changes the p-type tin-lead perovskite to n-type, increases the built-in potential, and decreases the open-circuit voltage (V _oc) loss in perovskite solar cells. With Br inclusion into the lattice and passivation by EDA, the highest power conversion efficiency of 21.74% and Voc of 0.86 V is achieved using Cs_0.025FA_0.475MA_0.5Sn_0.5Pb_0.5I_2.975Br_0.025 perovskite film with a bandgap of 1.25 eV.

Abstract

Tin-lead perovskite solar cells (PSCs) show inferior power conversion efficiency (PCE) than their Pb counterparts mainly because of the higher open-circuit voltage (V _oc) loss. Here, it is revealed that the p-type surface of perovskite transforms to n-type, based on post-treatment by a Lewis base, ethylenediamine. This approach forms a graded band structure owing to the rise of the Fermi-energy level at the surface of the perovskite layer, and increases the built-in potential from 0.56 to 0.76 V, which increases the V _oc by more than 100 mV. It is demonstrated that EDA can lower the defect density (Sn⁴⁺ amount) by screening perovskite against oxygen, and by bonding with undercoordinated Sn on the surface. This study further explores the role of Br anion inclusion in the perovskite lattice from the viewpoint of reducing the lattice strain and Urbach energy. Finally, a high V _oc of 0.86 V is obtained, corresponding to a voltage deficit of 0.39 V, using a perovskite absorber with a bandgap of 1.25 eV and the highest PCE (21.74%) reported so far for Sn-Pb PSCs is achieved.

A hydrophobic ammonium salt, 4-(trifluoromethyl) benzylamine, is introduced to form a quasi-2D hybrid perovskite by a one-step spin-coating method. Due to the relatively low surface energy of fluorinated molecules, an upper gradient low-dimensional structure is formed spontaneously from top to bottom, and more stable devices are obtained with a power conversion efficiency of 17.07%.

Abstract

Highly efficient and stable quasi-2D hybrid perovskite solar cells (PSCs) using hydrophobic 4-(trifluoromethyl) benzylamine (4TFBZA) as the spacer cation are successfully demonstrated. It is found that the incorporation of hydrophobic 4TFBZA into MAPbI₃ can effectively induce a spontaneous upper gradient 2D (SUG-2D) structure, passivate the trap states, and restrain the ion motion. Meanwhile, the strong hydrogen bonding of F···HN between 4TFBZA ions and methylamine ions can effectively suppress the decomposition of perovskite, which gives the device a better thermal stability. Besides, due to the SUG-2D structure with hydrophobic 4TFBZA, the device also exhibits a better moisture stability. The SUG-2D-structure-based device exhibits a power conversion efficiency of 17.07% with a high open-circuit voltage of 1.10 V and a notable fill factor of 71%. This work provides a new strategy for constructing efficient and stable quasi-2D PSCs, and it is an inspiration for the packaging strategy of perovskites.

Publication date: November 2021

Source: Nano Energy, Volume 89, Part A

Author(s): Po-Cheng Huang, Shao-Ku Huang, Ting-Chun Lai, Min-Chuan Shih, Hung-Chang Hsu, Chun-Hsiang Chen, Cheng-Chieh Lin, Chun-Hao Chiang, Chi-Ying Lin, Kazuhito Tsukagoshi, Chun-Wei Chen, Ya-Ping Chiu, Shiow-Fon Tsay, Ying-Chiao Wang

Just add (pseudo)halides: Progress made on the employment of halide and pseudo-halide additives in organo-metal perovskite solar cells is reviewed. Their function in morphology adjusting, phase stabilizing, energy-level adjusting, trap state passivation, and hysteresis elimination is detailed. A deep understanding of the relationship between halide/pseudo-halide additive and the improved properties of perovskite solar cells is presented.

Abstract

Perovskite solar cells (PSCs) are attracting a tremendous attention from the scientific community due to their excellent power conversion efficiency, low cost, and great promise for the future of solar energy. The best PSCs have already achieved a certified power conversion efficiency (PCE) of 25.5 % after an unprecedented rapid performance rise. However, high requirements with respect to large area, high-efficiency devices, and stability are still the challenges. Major efforts, especially for achieving a high degree of chemical control, have been made to reach these targets. The use of halide additives has played a critical role in improving the efficiency and stability. The present paper reviews the important breakthroughs in PSC technologies made by using halide additives, especially chloride, and pseudo-halide additives for the preparation of the perovskite layers, other layers, and interfaces of the devices. These additives help perovskite (PVK) crystallization and layer morphology control, grain boundary reduction, bulk and interface defects passivation, and so on. Normally, these halide additives play different roles depending on their categories and their location. Herein, recent progresses made due to additives employment in every possible layer of PSCs are reviewed, with focus on chloride, other halides, and pseudo-halides as additives in PVK films, halide additives in carrier transport layers, and at PVK-contact interfaces. Finally, an outlook of engineering of these additives in PSC progress is given.

Even without defect passivation, the surface recombination of perovskite solar cells can be suppressed by reducing the concentration of minority carriers at the front surface. By introducing a wide-gap perovskite, CsPbBr₃ nanocrystals, to the front surface, the inverted MAPbI₃ cells can achieve significant enhancement of open-circuit voltages without losing photocurrent.

A bandgap gradient at the front surface of solar absorbers can effectively suppress surface recombination while not affecting photocurrent. Herein, it is demonstrated that a front-surface gradient can be formed in an inverted perovskite cell by introducing perovskite quantum dots (QDs) between the hole-transporting layer (HTL) and the remaining absorber. Ultraviolet photoelectron spectroscopy reveals that, with the addition of CsPbBr₃ QDs onto the HTL substrate, the subsequently deposited MAPbI₃ is converted from mild p-type to n-type, and the resultant band alignment can effectively reduce the electron concentration at the front surface without significantly affecting hole extraction. Multiple independent characterizations further confirm the reduction of surface recombination. As a result, the inverted MAPbI₃ cells exhibit an open-circuit voltage of 1.154 V, which translates to a nonradiative recombination loss of 0.15 V and a power conversion efficiency of 20.51%.

Publication date: November 2021

Source: Nano Energy, Volume 89, Part A

Author(s): Fan Zhang, Shuai Ye, Hanhong Zhang, Feifan Zhou, Yuying Hao, Houzhi Cai, Jun Song, Junle Qu

Publication date: November 2021

Source: Nano Energy, Volume 89, Part A

Author(s): Gaopeng Wang, Kai Zhang, Zheng Wang, Jian Wang, Rongguo Xu, Lin Li, Xiuwen Xu, Yu Li, Shuang Xiao, Shizhao Zheng, Xiong Li, Shihe Yang

It is demonstrated that 1D perovskitoid based on 2-diethylaminoethylchloride cations can act as a template to induce 1D@3D perovskite structure, leading to smoother surface texture, longer charge-carrier lifetime, smaller residual tensile strain, and reduced surface-defect density in the perovskite film. With this strategy, highly efficient and stable 1D@3D PSCs with excellent reproducibility are realized.

Abstract

Longevity is a long-standing concern for organic–inorganic hybrid perovskite solar cells (PSCs). Recently, the use of low dimensional perovskite has been proven to be a promising strategy to improve the stability of PSCs. Herein, it is demonstrated that 1D perovskitoid based on 2-diethylaminoethylchloride cations can act as a template to induce 1D@3D perovskite structure, leading to smoother surface texture, longer charge-carrier lifetime, smaller residual tensile strain, and reduced surface-defect density in the perovskite film. With this strategy, highly efficient and stable 1D@3D PSC with excellent reproducibility, showing a champion power conversion efficiency (PCE) of 22.9% under standard AM 1.5 G one sun illumination is realized. The unencapsulated optimized devices can retain 94.7%, 92.4%, and 90.0% of their initial PCEs for 2100, 2200, and 2200 h under ambient air, 85 °C and illumination conditions, respectively.

A series of 8-hydroxyquinoline metal complexes are employed as cathode interfacial layer in inverted planar perovskite solar cells. The introduction of the interfacial layer significantly accelerates the charge transfer and blocks the ion diffusion, leading to better device performance and stability.

Abstract

Ion migration is a crucial factor influencing the stability of perovskite solar cells. Insertion of an interfacial layer between the electron-transporting layer and the cathode is shown to be an effective way to enhance the performance of devices. However, exploring more effective interfacial materials to block ion migration and thus enhance the device stability is still needed. Herein, a series of 8-hydroxyquinoline metal complexes are employed as cathode interfacial layers (CILs) in inverted planar perovskite solar cells. The devices with CILs exhibit better performance, stability, and reproducibility than the control device without CILs. The introduction of the CILs forms a better energy match between the [6,6]-phenyl-C61-butyric acid methyl ester layer and the cathode, reduces the contact resistance, accelerates the charge transfer, and suppresses non-radiative recombination. Moreover, the CILs protect the device from moisture and block the ion diffusions, which is beneficial for device stability. After optimization, the best power conversion efficiency of 20.6% is obtained by using 8-hydroxyquinoline aluminum (Alq₃) as a CIL, and the efficiency remains 85% of its initial value after 800 h continuous illumination.

Conjugated polyelectrolyte is inserted between NiO _x HTLs and perovskite active layer to reduce interfacial Ni²⁺ vacancies trap density. This simultaneously passivates trap-mediated Shockley–Read–Hall recombination and enhances quasi-Fermi level splitting, yielding an increase in open-circuit voltage (V _OC) values to 1.14 V.

Abstract

Nickel oxide (NiO _x ) is desirable hole selective material (HSMs) for perovskite photovoltaics because of the characteristic in stability and low cost. However, they deliver limited open-circuit voltage (V _OC) compared to some organic HSMs. As it is known, the performance of perovskite solar cells is predominantly limited by trap-assisted non-radiative recombination at the perovskite/hole-selective layer interfaces. A typical lithium-doping strategy leads to the valence-band maximum shift and the electronic levels of NiO _x can be tuned robustly to match perovskite active layer in perovskite solar cells. More critically, carrier dynamics studies demonstrate another critical PN4N interlayer strategy reduced interfacial density of defect sites and trap-assisted recombination. These merits contribute coordinately to lower energy loss across the perovskite/NiO _x interface and facilitate charge transport process through the relevant interface, yielding V _OC values increase to 1.14 V and power conversion efficiencies over 20%.

A “precursor to perovskite-like template to perovskite’ (PPP) strategy is proposed to control phase transition and to suppress deep-level defect formation during perovskite crystallization. The defect density is reduced by an order of magnitude and the carrier lifetime is doubled, yielding an impressive power conversion efficiency of 22.8%. Universality of this strategy is also demonstrated.

Tunable crystal growth offering highly aligned perovskite crystallites with suppressed deep-level defects is vital for efficient charge transport, which in turn significantly influences the power conversion efficiency (PCE) of perovskite solar cells (PSCs). Herein, a “precursor to perovskite-like template to perovskite” (PPP) growth strategy is developed, using either MAAc or GuaCl precursor to induce a sacrificial thermal–unstable perovskite-like template for (FAPbI₃) _x (MAPbI₃) _y perovskite growth. The self-sacrificed intermediate template induces the formation of highly aligned perovskite crystals with greatly enhanced film crystallinity and suppresses deep-level defect formation. Furthermore, it is proved that MAAc or GuaCl completely evaporates during the high-temperature annealing process. The reduction in defect densities and nonradiative recombination enhances both carrier lifetime and charge dynamics, yielding impressive PCEs of 22.3% and 22.8% with a high open-circuit voltage (V _OC) of 1.16 V and an incredible fill factor (FF) of 81.5% and 79.4% for MAAc- and GuaCl-based devices, respectively. These results suggest that the formation of the thermal–unstable perovskite-like sacrificial template is a promising strategy to restrain the deep-level defects in perovskite films toward the attainment of highly efficient and stable large-scale PSCs as well as other perovskite-based electronics.

The vacuum-deposited fluorinated analogue Spiro-OMeTAD is introduced as a hole transport layer in the inverted perovskite solar cells. Through the suitable energy level and improved crystallinity along the π–π stacking direction with the uniform surface morphology, the device performance and stability are notably improved. Furthermore, large-area and scalable device fabrication with good reliability is demonstrated using the all-vacuum deposition process.

Developing scalable technologies in perovskite solar cells (PSCs), including the deposition of uniform perovskite photoactive layers and charge transport layers, is critical for successfully migrating the recently developed advances in the PSC community toward industrialization. Herein, efficient and stable large-area PSCs using vacuum-deposited fluorinated analogue Spiro-OMeTAD (Spiro-mF) and methylammonium lead iodide (MAPbI₃) as hole transport and absorber layers, respectively, are demonstrated. The vacuum-deposited Spiro-mF exhibits improved crystallinity compared with the solution-processed counterpart through the enhanced molecular orientation along the π–π stacking direction, promoting the charge transport characteristics. Also, its uniform surface morphology contributes to the better quality crystallinity of the overlying perovskite film, which altogether leads to improved device performance and operational stability. Moreover, the all-vacuum deposition process allows the fabrication of large-area (250 mm²) and scalable (75 × 75 mm²) PSCs with excellent reliability in device performance.

Herein, a fully low-temperature solution-processed colloidal SnO₂-assisted CdS electron transport layer for planar CH₃NH₃PbI₃ perovskite solar cells. The presence of SnO₂ underlayer allows the decrease in shunt current leakage and the formation of cascade band structure, which promote the electron extraction at the ETL/perovskite interface. The corresponding device delivers an appreciable efficiency of 16.26%, doubling that of conventional CdS-based device.

The cadmium sulfide (CdS) is a promising electron transport layer (ETL) material for perovskite solar cells (PSCs) due to its low photocatalytic activity toward perovskite materials under UV light. The critical problem responsible for the moderate performance of CdS-based PSCs is the parasitic light absorption of CdS, which drives researchers to deposit ultrathin ETLs. However, the ultrathin ETL often involves the undesirable shunt current leakage because of the direct contact between conducting substrate and perovskite layer. Herein, a fully low-temperature solution-processed colloidal SnO₂-assisted CdS (S-CdS) ETL for planar CH₃NH₃PbI₃ PSCs is constructed. The detailed characterizations of morphological, optical, and energy levels confirm that the assistance of colloidal SnO₂ provides the ameliorated continuity, reduces surface roughness and superior wettability of ETLs for high-quality perovskite formation as well as the favorable cascade band structure for efficient charge transfer. The study of charge transfer mechanisms reveals that the S-CdS ETL effectively inhibits the shunt leakage, promotes the electron extraction and suppresses the charge recombination at the ETL/perovskite interface. Consequently, the S-CdS ETL-based PSCs deliver an appreciable efficiency of 16.26%, doubling that of conventional CdS-based devices. To the best of our knowledge, this value is the champion efficiency reported for CdS-based CH₃NH₃PbI₃ PSCs.

The research progress on metal halide perovskite solar minimodules and their improvements in efficiency and stability is reviewed.

The rapid development of perovskite solar cells (PSCs) in view of efficiency during the past decade has made this emerging photovoltaic (PV) technology a promising competitor in the PV market. In the next step, PSCs need be manufactured into module scale to meet the commercialization requirements for further practical application. Demonstrations of perovskite solar modules (PSMs) and their improvements in efficiency and stability have recently become an intense area of research activities. Minimodules with the size suitable for laboratory investigation are naturally recognized as a desirable model for the study of PSMs. Herein, the recent progress and challenges in perovskite solar minimodules and the efforts to improve their scalable fabrication, efficiency, and stability are reviewed. Minimodule architectures, minimodule fabrication, and progress in the scalable deposition of perovskite and charge-transport layers as well as minimodule encapsulation are also discussed.

Solution processing of semiconductors is highly promising for the high-throughput production of cost-effective electronics and optoelectronics. Although hybrid perovskites have potential in various device applications, challenges remain in the development of high-quality materials with simultaneously improved processing reproducibility and scalability. Here, we report a liquid medium annealing (LMA) technology that creates a robust chemical environment and constant heating field to modulate crystal growth over the entire film. Our method produces films with high crystallinity, fewer defects, desired stoichiometry, and overall film homogeneity. The resulting perovskite solar cells (PSCs) yield a stabilized power output of 24.04% (certified 23.7%, 0.08 cm²) and maintain 95% of their initial power conversion efficiency (PCE) after 2000 hours of operation. In addition, the 1-cm² PSCs exhibit a stabilized power output of 23.15% (certified PCE 22.3%) and keep 90% of their initial PCE after 1120 hours of operation, which illustrates their feasibility for scalable fabrication. LMA is less climate dependent and produces devices in-house with negligible performance variance year round. This method thus opens a new and effective avenue to improving the quality of perovskite films and photovoltaic devices in a scalable and reproducible manner.

A hydrophobic p-type semiconducting additive, fluorinated-gold-clusters, is used as a bifunctional interfacial mediator to efficiently modulate the carrier dynamics of perovskite and restrain the perovskite from degradation by external environmental stimuli, which results in an n–i–p perovskite solar cell with a champion efficiency up to 24.02% and moisture stability over 10 000 h in relative humidity of 75%.

Abstract

Tackling the interfacial loss in emerged perovskite-based solar cells (PSCs) to address synchronously the carrier dynamics and the environmental stability, has been of fundamental and viable importance, while technological hurdles remain in not only creating such interfacial mediator, but the subsequent interfacial embedding in the active layer. This article reports a strategy of interfacial embedding of hydrophobic fluorinated-gold-clusters (FGCs) for highly efficient and stable PSCs. The p-type semiconducting feature enables the FGC efficient interfacial mediator to improve the carrier dynamics by reducing the interfacial carrier transfer barrier and boosting the charge extraction at grain boundaries. The hydrophobic tails of the gold clusters and the hydrogen bonding between fluorine groups and perovskite favor the enhancement of environmental stability. Benefiting from these merits, highly efficient formamidinium lead iodide PSCs (champion efficiency up to 24.02%) with enhanced phase stability under varied relative humidity (RH) from 40% to 95%, as well as highly efficient mixed-cation PSCs with moisture stability (RH of 75%) over 10 000 h are achieved. It is thus inspiring to advance the development of highly efficient and stable PSCs via interfacial embedding laser-generated additives for improved charge transfer/extraction and environmental stability.

A combined approach of simulation and experiment unravels the origin of very high external quantum efficiencies (EQEs up to 98% in the literature), which are frequently reported for highly efficient perovskite solar cells. The high refractive index of the perovskite and the thickness of the underlying transparent electrode are identified to mainly govern light in-coupling into the active layer.

With the emergence of highly efficient perovskite solar cells in both single- and multijunction architectures, there is an abundance of reports of extremely high external quantum efficiencies (EQE) up to 98%. Typically, the spectral maximum of the EQE is found in the range between 400 and 500 nm, which is even more surprising, as the transmittance of typically used indium tin oxide (ITO)/glass substrates does not exceed 90% in this wavelength range. Herein, the root cause of the high EQE values by a combination of experimental data and optical simulations is analyzed and explained. It is shown that the high refractive index of the perovskite absorber is strongly increasing the transmittance of incident light into the active perovskite layer, while the spectral distribution and ultimately the spectral position of the peak in the transmittance spectrum are strongly affected by the thickness and optical properties of the underlying transparent electrode.

A versatile co-evaporation approach to create perovskites layers with graded energy levels favorable for different device architectures is demonstrated. The p-i-n perovskite solar cells, incorporating co-evaporated MAPbI₃ with customized graded Fermi levels, achieve power conversion efficiency over 20% with different hole transporting layers and champion values of 20.6%, 19.1%, and 17.2% for 0.086, 1, and 1.96 cm² active areas, respectively.

Abstract

Recent progress of vapor-deposited perovskite solar cells (PSCs) has proved the feasibility of this deposition method in achieving promising photovoltaic devices. For the first time, it is probed the versatility of the co-evaporation process in creating perovskite layers customizable for different device architectures. A gradient of composition is created within the perovskite films by tuning the background chamber pressure during the growth process. This method leads to co-evaporated MAPbI₃ film with graded Fermi levels across the thickness. Here it is proved that this growth process is beneficial for p-i-n PSCs as it can guarantee a favorable energy alignment at the charge selective interfaces. Co-evaporated p-i-n PSCs, with different hole transporting layers, consistently achieve power conversion efficiency (PCE) over 20% with a champion value of 20.6%, one of the highest reported to date. The scaled-up p-i-n PSCs, with active areas of 1 and 1.96 cm², achieved the record PCEs of 19.1% and 17.2%, respectively, while the flexible PSCs reached a PCE of 19.3%. Unencapsulated PSCs demonstrate remarkable long-term stability, retaining ≈90% of their initial PCE when stored in ambient for 1000 h. These PSCs also preserve over 80% of their initial PCE after 500 h of thermal aging at 85 °C.

Co-evaporation methylammonium formamidinium lead iodide perovskites are investigated and different aspects of stability are addressed. The influence of the perovskite composition on the performance and the long-term stability of the resulting solar cells is studied. Monolithic fully textured perovskite/silicon tandem solar cells with co-evaporated perovskite absorber are realized. These tandem cells reach an efficiency of 24.6% and exhibit minimal reflection losses.

Abstract

Formamidinium iodide (FAI) based perovskite absorbers have been shown to be ideal candidates for highly efficient and operationally stable perovskite solar cells (PSC). A major challenge for formamidinium lead iodide (FAPbI₃) is to suppress the phase transition from the photoactive black phase into yellow nonperovskite δ-phase. Several approaches to stabilize the black phase have been developed for solution-based perovskites, whereas so far, vacuum-deposited FAPbI₃ has rarely been reported. This study demonstrates the preparation of FAPbI₃ by co-evaporation and discusses the influence of the subjacent hole transporting layer (HTL) on its phase stability. By using FAI excess in the evaporation process in combination with phosphonic acids groups from the HTL, the black perovskite phase is stabilized at room temperature. Further addition of 32–59% methylammonium iodide (MAI) during the co-evaporation process leads to good absorption properties and high PSC efficiencies of 20.4%. In addition, excellent stability is achieved for optimized MAI to FAI ratios, maintaining 100% of the initial PSC performance after 1000 h under constant operation. This highly stable perovskite composition enables the first monolithic fully textured perovskite/silicon tandem solar cells with co-evaporated perovskite absorbers. Due to the conformally covered pyramid texture, these tandem cells show minimal reflection losses and reach an efficiency of 24.6%.

Publication date: August 2021

Source: Nano Today, Volume 39

Author(s): Lingbo Jia, Fanyang Huang, Honghe Ding, Chuang Niu, Yanbo Shang, Wanpei Hu, Xingcheng Li, Xin Yu, Xiaofen Jiang, Ruiguo Cao, Junfa Zhu, Guan-Wu Wang, Muqing Chen, Shangfeng Yang

Dipole–dipole interaction induced self-assembly of phenoxazine-based hole-transporting material, N01, is achieved by introducing a hexyl bromide side-chain to tune its self-assembling properties. N01 exhibits a higher intrinsic hole mobility and more favorable interfacial properties for hole transport, extraction and perovskite growth, with a conversion efficiency of 21.85 % to be realized in an inverted PSC.

Abstract

Delicately designed dopant-free hole-transporting materials (HTMs) with ordered structure have become one of the major strategies to achieve high-performance perovskite solar cells (PSCs). In this work, we report two donor-π linker-donor (D-π-D) HTMs, N01 and N02, which consist of facilely synthesized 4,8-di(n-hexyloxy)-benzo[1,2-b:4,5-b′]dithiophene as a π linker, with 10-bromohexyl-10H-phenoxazine and 10-hexyl-10H-phenoxazine as donors, respectively. The N01 molecules form a two-dimensional conjugated network governed by C−H⋅⋅⋅O and C−H⋅⋅⋅Br interaction between phenoxazine donors, and synchronously construct a three-dimension lamellar structure with the aid of interlaminar π–π interaction. Consequently, N01 as a dopant-free small-molecule HTM exhibits a higher intrinsic hole mobility and more favorable interfacial properties for hole transport, hole extraction and perovskite growth, enabling an inverted PSC to achieve a very impressive power conversion efficiency of 21.85 %.