Dopant‐Free Hole Transporting Polymers for High Efficiency,Environmentally Stable Perovskite Solar Cells

Over the past five years, a rapid progress in organometal‐halide perovskite solar cells has greatly influenced emerging solar energy science and technology. In perovksite solar cells, the overlying hole transporting material (HTM) is critical for achieving high power conversion efficiencies (PCEs) and for protecting the air‐sensitive perovskite active layer. This study reports the synthesis and implementation of a new polymeric HTM series based on semiconducting 4,8‐dithien‐2‐yl‐benzo[1,2‐d;4,5‐d′]bistriazole‐alt‐benzo[1,2‐b:4,5‐b′]dithiophenes (pBBTa‐BDTs), yielding high PCEs and environmentally‐stable perovskite cells. These intrinsic (dopant‐free) HTMs achieve a stabilized PCE of 12.3% in simple planar heterojunction cells—the highest value to date for a polymeric intrinsic HTM. This high performance is attributed to efficient hole extraction/collection (the most efficient pBBTa‐BDT is highly ordered and orients π‐face‐down on the perovskite surface) and balanced electron/hole transport. The smooth, conformal polymer coatings suppress aerobic perovskite film degradation, significantly enhancing the solar cell 85 °C/65% RH PCE stability versus typical molecular HTMs.     

Improved Optics in Monolithic Perovskite/Silicon Tandem Solar Cells with a Nanocrystalline Silicon Recombination Junction

Perovskite/silicon tandem solar cells are increasingly recognized as promi­sing candidates for next‐generation photovoltaics with performance beyond the single‐junction limit at potentially low production costs. Current designs for monolithic tandems rely on transparent conductive oxides as an intermediate recombination layer, which lead to optical losses and reduced shunt resistance. An improved recombination junction based on nanocrystalline silicon layers to mitigate these losses is demonstrated. When employed in monolithic perovskite/silicon heterojunction tandem cells with a planar front side, this junction is found to increase the bottom cell photocurrent by more than 1 mA cm^?2. In combination with a cesium‐based perovskite top cell, this leads to tandem cell power‐conversion efficiencies of up to 22.7% obtained from J–V measurements and steady‐state efficiencies of up to 22.0% during maximum power point tracking. Thanks to its low lateral conductivity, the nanocrystalline silicon recombination junction enables upscaling of monolithic perovskite/silicon heterojunction tandem cells, resulting in a 12.96 cm² monolithic tandem cell with a steady‐state efficiency of 18%.     

Rational Design of Dopant‐Free Coplanar D‐π‐D Hole‐Transporting Materials for High‐Performance Perovskite Solar Cells with Fill Factor Exceeding 80%

In this paper, two novel D‐π‐D hole‐transporting materials (HTM) are reported, abbreviated as BDT‐PTZ and BDT‐POZ , which consist of 4,8‐di(hexylthio)‐benzo[1,2‐b:4,5‐b′]dithiophene (BDT) as π‐conjugated linker, and N‐(6‐bromohexyl) phenothiazine (PTZ)/N‐(6‐bromohexyl) phenoxazine (POZ) as donor units. The above two HTMs are deployed in p‐i‐n perovskite solar cells (PSCs) as dopant‐free HT layers, exhibiting excellent power conversion efficiencies of 18.26% and 19.16%, respectively. Particularly, BDT‐POZ demonstrates a superior fill factor of 81.7%, which is consistent with its more efficient hole extraction and transport verified via steady‐state/transient fluorescence spectra and space‐charge‐limited current technique. Single‐crystal X‐ray diffraction characterization implies these two molecules present diverse packing tendencies, which may account for various interfacial hole‐transport ability in PSCs.     

Highly Efficient and Stable Perovskite Solar Cells Using a Dopant‐Free Inexpensive Small Molecule as the Hole‐Transporting Material

The hole transporting layer (HTL) plays an important role in realizing efficient and stable perovskite solar cells (PSCs). In spite of intensive research efforts toward the development of HTL materials, low‐cost, dopant‐free hole transporting materials that lead to efficient and stable PSCs remain elusive. Herein, a simple polycyclic heteroaromatic hydrocarbon‐based small molecule, 2,5,9,12‐tetra(tert‐butyl)diacenaphtho[1,2‐b:1′,2′‐d]thiophenen, as an efficient HTL material in PSCs is presented. This molecule is easy to synthesize and inexpensive. It is hydrophobic and exhibits excellent film‐forming properties on perovskites. It has unusually high hole mobility and a desirable highest occupied molecular orbital energy level, making it an ideal HTL material. PSCs fabricated using both the n‐i‐p planar and mesoscopic architectures with this compound as the HTL show efficiencies as high as 15.59% and 18.17%, respectively, with minimal hysteresis and high long term stability under ambient conditions.     

Low‐Temperature Solution‐Processed CuCrO2 Hole‐Transporting Layer for Efficient and Photostable Perovskite Solar Cells

Organic–inorganic hybrid perovskite solar cells (PVSCs) have become the front‐running photovoltaic technology nowadays and are expected to profoundly impact society in the near future. However, their practical applications are currently hampered by the challenges of realizing high performance and long‐term stability simultaneously. Herein, the development of inverted PVSCs is reported based on low temperature solution‐processed CuCrO₂ nanocrystals as a hole‐transporting layer (HTL), to replace the extensively studied NiO_x counterpart due to its suitable electronic structure and charge carrier transporting properties. A ≈45 nm thick compact CuCrO₂ layer is incorporated into an inverted planar configuration of indium tin oxides (ITO)/c‐CuCrO₂/perovskite/[6,6]‐phenyl‐C61‐butyric acid methyl ester (PCBM)/bathocuproine (BCP)/Ag, to result in the high steady‐state power conversion efficiency of 19.0% versus 17.1% for the typical low temperature solution‐processed NiO_x‐based devices. More importantly, the optimized CuCrO₂‐based device exhibits a much enhanced photostability than the reference device due to the greater UV light‐harvesting of the CuCrO₂ layer, which can efficiently prevent the perovskite film from intense UV light exposure to avoid associated degradation. The results demonstrate the promising potential of CuCrO₂ nanocrystals as an efficient HTL for realizing high‐performance and photostable inverted PVSCs.     

Low‐Cost N,N′‐Bicarbazole‐Based Dopant‐Free Hole‐Transporting Materials for Large‐Area Perovskite Solar Cells

Despite the recent unprecedented development of efficient dopant‐free hole transporting materials (HTMs) for high‐performance perovskite solar cells (PSCs) on small‐area devices (≤0.1 cm²), low‐cost dopant‐free HTMs for large‐area PSCs (≥1 cm²) with high power conversion efficiencies (PCEs) have rarely been reported. Herein, two novel HTMs, 3,3′,6,6′ (or 2,2′,7,7′)‐tetrakis(N,N′‐di‐p‐methoxyphenylamine)‐N,N′‐bicarbazole (3,6 BCz‐OMeTAD or 2,7 BCz‐OMeTAD), are synthesized via an extremely simple route from very cheap raw materials. Owing to their excellent film‐forming abilities and matching energy levels, 3,6 BCz‐OMeTAD and 2,7 BCz‐OMeTAD can be successfully employed as a perfect ultrathin (≈30 nm) hole transporting layer in large‐area PSCs up to 1 cm². The 3,6 BCz‐OMeTAD and 2,7 BCz‐OMeTAD based large‐area PSCs show highest PCEs up to 17.0% and 17.6%, respectively. More importantly, high performance large‐area PSCs based on 2,7 BCz‐OMeTAD retain 90% of the initial efficiency after 2000 h storage in an ambient environment without encapsulation.     

Efficient Indium‐Doped TiOx Electron Transport Layers for High‐Performance Perovskite Solar Cells and Perovskite‐Silicon Tandems

In addition to a good perovskite light absorbing layer, the hole and electron transport layers play a crucial role in achieving high‐efficiency perovskite solar cells. Here, a simple, one‐step, solution‐based method is introduced for fabricating high quality indium‐doped titanium oxide electron transport layers. It is shown that indium‐doping improves both the conductivity of the transport layer and the band alignment at the ETL/perovskite interface compared to pure TiO₂, boosting the fill‐factor and voltage of perovskite cells. Using the optimized transport layers, a high steady‐state efficiency of 17.9% for CH₃NH₃PbI₃‐based cells and 19.3% for Cs_0.05(MA_0.17FA_0.83)_0.95Pb(I_0.83Br_0.17)₃‐based cells is demonstrated, corresponding to absolute efficiency gains of 4.4% and 1.2% respectively compared to TiO₂‐based control cells. In addition, a steady‐state efficiency of 16.6% for a semi‐transparent cell is reported and it is used to achieve a four‐terminal perovskite‐silicon tandem cell with a steady‐state efficiency of 24.5%.     

LiTFSI‐Free Spiro‐OMeTAD‐Based Perovskite Solar Cells with Power Conversion Efficiencies Exceeding 19%

To date, the most efficient perovskite solar cells (PSCs) employ an n–i–p device architecture that uses a 2,2′,7,7′‐tetrakis(N,N‐di‐p‐methoxyphenyl‐amine)‐9,9′‐spirobifluorene (spiro‐OMeTAD) hole‐transporting material (HTM), which achieves optimum conductivity with the addition of lithium bis(trifluoromethane)sulfonimide (LiTFSI) and air exposure. However, this additive along with its oxidation process leads to poor reproducibility and is detrimental to stability. Herein, a dicationic salt spiro‐OMeTAD(TFSI)₂, is employed as an effective p‐dopant to achieve power conversion efficiencies of 19.3% and 18.3% (apertures of 0.16 and 1.00 cm²) with excellent reproducibility in the absence of LiTFSI and air exposure. As far as it is known, these are the highest‐performing n–i–p PSCs without LiTFSI or air exposure. Comprehensive analysis demonstrates that precise control of the proportion of [spiro‐OMeTAD]⁺ directly provides high conductivity in HTM films with low series resistance, fast hole extraction, and lower interfacial charge recombination. Moreover, the spiro‐OMeTAD(TFSI)₂‐doped devices show improved stability, benefitting from well‐retained HTM morphology without forming aggregates or voids when tested under an ambient atmosphere. A facile approach is presented to fabricate highly efficient PSCs by replacing LiTFSI with spiro‐OMeTAD(TFSI)₂. Furthermore, this study provides an insight into the relationship between device performance and the HTM doping level.     

High Electron Affinity Enables Fast Hole Extraction for Efficient Flexible Inverted Perovskite Solar Cells

Inverted perovskite solar cells (PSCs) with low‐temperature processed hole transporting materials (HTMs) suffer from poor performance due to the inferior hole‐extraction capability at the HTM/perovskite interfaces. Here, molecules with controlled electron affinity enable a HTM with conductivity improved by more than ten times and a decreased energy gap between the Fermi level and the valence band from 0.60 to 0.24 eV, leading to the enhancement of hole‐extraction capacity by five times. As a result, the 3,6‐difluoro‐2,5,7,7,8,8‐hexacyanoquinodimethane molecules are used for the first time enhancing open‐circuit voltage (V_oc) and fill factor (FF) of the PSCs, which enable rigid‐and flexible‐based inverted perovskite devices achieving highest power conversion efficiencies of 22.13% and 20.01%, respectively. This new method significantly enhances the V_oc and FF of the PSCs, which can be widely combined with HTMs based on not only NiO_x but also PTAA, PEDOTT:PSS, and CuSCN, providing a new way of realizing efficient inverted PSCs.     

4‐Tert‐butylpyridine Free Organic Hole Transporting Materials for Stable and Efficient Planar Perovskite Solar Cells

4‐Tert ‐butylpyridine (t BP) is an important additive in triarylamine‐based organic hole‐transporting materials (HTMs) for improving the efficiency and steady‐state performance of perovskite solar cells (PVSCs). However, the low boiling point of t BP (196 °C) significantly affects the long‐term stability and device performance of PVSCs. Herein, the design and synthesis of a series of covalently linked Spiro[fluorene‐9,9′‐xanthene] (SFX)‐based organic HTMs and pyridine derivatives to realize efficient and stable planar PVSCs are reported. One of the tailored HTMs, N2,N2,N7,N7‐tetrakis(4‐methoxyphenyl)‐3′,6′‐bis(pyridin‐4‐ylmethoxy) spiro[fluorene‐9,9′‐xanthene]‐2,7‐diamine ( XPP ) with two para‐position substituted pyridines that immobilized on the SFX core unit shows a high power conversion efficiency (PCE) of 17.2% in planar CH₃NH₃PbI₃‐based PVSCs under 100 mW cm^?2 AM 1.5G solar illumination, which is much higher than the efficiency of 5.5% that using the well‐known 2,2′,7,7′‐tetrakis‐(N ,N ‐di‐p ‐methoxy‐phenyl‐amine)9,9′‐spirobifluorene (Spiro‐OMeTAD) as HTM (without t BP) under the same condition. Most importantly, the pyridine‐functionalized HTM‐based PVSCs without t BP as additive show much better long‐term stability than that of the state‐of‐the‐art HTM Spiro‐OMeTAD‐based solar cells that containing t BP as additive. This is the first case that the t BP‐free HTMs are demonstrated in PVSCs with high PCEs and good stability. It paves the way to develop highly efficient and stable t BP‐free HTMs for PVSCs toward commercial applications.     

Metal‐Oxide‐Free Methylammonium Lead Iodide Perovskite‐Based Solar Cells: the Influence of Organic Charge Transport Layers

Metal‐oxide‐free methylammonium lead iodide perovskite‐based solar cells are prepared using a dual‐source thermal evaporation method. This method leads to high quality reproducible films with large crystal domain sizes allowing for an in depth study of the effect of perovskite film thickness and the nature of the electron and hole blocking layers on the device performance. The power conversion efficiency increases from 4.7% for a device with only an organic electron blocking layer to almost 15% when an organic hole blocking layer is also employed. In addition to the in depth study on small area cells, larger area cells (approx. 1 cm^?2) are prepared and exhibit efficiencies in excess of 10%.     

Ionic Reactivity at Contacts and Aging of Methylammonium Lead Triiodide Perovskite Solar Cells

Hybrid lead halide perovskites have reached very large solar to electricity power conversion efficiencies, in some cases exceeding 20%. The most extensively used perovskite‐based solar cell configuration comprises CH₃NH₃PbI₃ (MAPbI₃) in combination with electron (TiO₂) and hole 2,2′,7,7′‐tetrakis(N,N‐di‐p‐methoxyphenylamine)‐9,9‐spiro‐bifluorene (spiro‐OMeTAD) selective contacts. The recognition that the solar cell performance is heavily affected by time scale of the measurement and preconditioning procedures has raised many concerns about the stability of the device and reliability for long‐time operation. Mechanisms at contacts originate observable current–voltage distortions. Two types of reactivity sources have been identified here: (i) weak Ti–I–Pb bonds that facilitate interfacial accommodation of moving iodine ions. This interaction produces a highly reversible capacitive current originated at the TiO₂/MAPbI₃ interface, and it does not alter steady‐state photovoltaic features. (ii) An irreversible redox peak only observable after positive poling at slow scan rates. It corresponds to the chemical reaction between spiro‐OMeTAD⁺ and migrating I^? which progressively reduces the hole transporting material conductivity and deteriorates solar cell performance.     

Elucidating the Role of a Tetrafluoroborate‐Based Ionic Liquid at the n‐Type Oxide/Perovskite Interface

Halide perovskites are currently one of the most heavily researched emerging photovoltaic materials. Despite achieving remarkable power conversion efficiencies, perovskite solar cells have not yet achieved their full potential, with the interfaces between the perovskite and the charge‐selective layers being where most recombination losses occur. In this study, a fluorinated ionic liquid (IL) is employed to modify the perovskite/SnO₂ interface. Using Kelvin probe and photoelectron spectroscopy measurements, it is shown that depositing the perovskite onto an IL‐treated substrate results in the crystallization of a perovskite film which has a more n‐type character, evidenced by a decrease of the work function and a shift of the Fermi level toward the conduction band. Photoluminescence spectroscopy and time‐resolved microwave conductivity are used to investigate the optoelectronic properties of the perovskite grown on neat and IL‐modified surfaces and it is found that the modified substrate yields a perovskite film which exhibits an order of magnitude lower trap density than the control. When incorporated into solar cells, this interface modification results in a reduction in the current–voltage hysteresis and an improvement in device performance, with the best performing devices achieving steady‐state PCEs exceeding 20%.     

Recombination in Polymer:Fullerene Solar Cells with Open‐Circuit Voltages Approaching and Exceeding 1.0 V

Polymer:fullerene solar cells are demonstrated with power conversion efficiencies over 7% with blends of PBDTTPD and PC₆₁BM. These devices achieve open‐circuit voltages (V_oc) of 0.945 V and internal quantum efficiencies of 88%, making them an ideal candidate for the large bandgap junction in tandem solar cells. V_oc’s above 1.0 V are obtained when the polymer is blended with multiadduct fullerenes; however, the photocurrent and fill factor are greatly reduced. In PBDTTPD blends with multiadduct fullerene ICBA, fullerene emission is observed in the photoluminescence and electroluminescence spectra, indicating that excitons are recombining on ICBA. Voltage‐dependent, steady state and time‐resolved photoluminescence measurements indicate that energy transfer occurs from PBDTTPD to ICBA and that back hole transfer from ICBA to PBDTTPD is inefficient. By analyzing the absorption and emission spectra from fullerene and charge transfer excitons, we estimate a driving free energy of –0.14 ± 0.06 eV is required for efficient hole transfer. These results suggest that the driving force for hole transfer may be too small for efficient current generation in polymer:fullerene solar cells with V_oc values above 1.0 V and that non‐fullerene acceptor materials with large optical gaps (>1.7 eV) may be required to achieve both near unity internal quantum efficiencies and values of V_oc exceeding 1.0 V.     

Mixed 3D–2D Passivation Treatment for Mixed‐Cation Lead Mixed‐Halide Perovskite Solar Cells for Higher Efficiency and Better Stability

Layered low‐dimensional perovskite structures employing bulky organic ammonium cations have shown significant improvement on stability but poorer performance generally compared to their 3D counterparts. Here, a mixed passivation (MP) treatment is reported that uses a mixture of bulky organic ammonium iodide (iso‐butylammonium iodide, iBAI) and formammidinium iodide (FAI), enhancing both power conversion efficiency and stability. Through a combination of inactivation of the interfacial trap sites, characterized by photoluminescence measurement, and formation of an interfacial energetic barrier by which ionic transport is reduced, demonstrated by Kelvin probe force microscopy, MP treatment of the perovskite/hole transport layer interface significantly suppresses photocurrent hysteresis. Using this MP treatment, the champion mixed‐halide perovskite cell achieves a reverse scan and stabilized power conversion efficiency of 21.7%. Without encapsulation, the devices show excellent moisture stability, sustaining over 87% of the original performance after 38 d storage in ambient environment under 75 ± 20% relative humidity. This work shows that FAI/ i BAI, is a new and promising material combination for passivating perovskite/selective‐contact interfaces.     

Vacuum‐Assisted Growth of Low‐Bandgap Thin Films (FA0.8MA0.2Sn0.5Pb0.5I3) for All‐Perovskite Tandem Solar Cells

All‐perovskite multijunction photovoltaics, combining a wide‐bandgap (WBG) perovskite top solar cell (E_G ≈1.6–1.8 eV) with a low‐bandgap (LBG) perovskite bottom solar cell (E_G < 1.3 eV), promise power conversion efficiencies (PCEs) >33%. While the research on WBG perovskite solar cells has advanced rapidly over the past decade, LBG perovskite solar cells lack PCE as well as stability. In this work, vacuum‐assisted growth control (VAGC) of solution‐processed LBG perovskite thin films based on mixed Sn–Pb perovskite compositions is reported. The reported perovskite thin films processed by VAGC exhibit large columnar crystals. Compared to the well‐established processing of LBG perovskites via antisolvent deposition, the VAGC approach results in a significantly enhanced charge‐carrier lifetime. The improved optoelectronic characteristics enable high‐performance LBG perovskite solar cells (1.27 eV) with PCEs up to 18.2% as well as very efficient four‐terminal all‐perovskite tandem solar cells with PCEs up to 23%. Moreover, VAGC leads to promising reproducibility and potential in the fabrication of larger active‐area solar cells up to 1 cm².     

Dominating Energy Losses in NiO p‐Type Dye‐Sensitized Solar Cells

Nickel oxide based p‐type dye‐sensitized solar cells (DSCs) are limited in their efficiencies by poor fill factors (FFs). This work explores the origins of this limitation. Transient absorption spectroscopy identifies fast recombination between the injected hole and the dye anion under applied load as one of the predominant reasons for the poor FF of NiO‐based DSCs. A reduced hole injection efficiency, η_INJ, under applied load is found to play an equally important role. Both, the dye regeneration yield, Φ_REG, and η_INJ decrease by approximately 40%–50% when moving from short‐ to open‐circuit conditions. Spectroelectrochemical measurements reveal that the electrochromic properties of NiO are a further limiting factor for the device performance leading to variable light‐harvesting efficiencies, η_LH, under applied load. The peak light‐harvesting efficiency decreases from 63% at short circuit to 57% at 600 mV reducing the FF of NiO DSCs by 5%. This effect is expected to be more pronounced for future devices with higher operating voltages. Incident, photon‐to‐electron conversion efficiency front–back analysis at applied bias is utilized to characterize the interfacial charge recombination. It is found that the recombination between the injected hole and the redox mediator has a surprisingly small effect on the FF.     

Cesium Doped NiOx as an Efficient Hole Extraction Layer for Inverted Planar Perovskite Solar Cells

Organic–inorganic hybrid perovskite solar cells have resulted in tremendous interest in developing next generation photovoltaics due to high record efficiency exceeding 22%. For inverted structure perovskite solar cells, the hole extraction layers play a significant role in achieving efficient and stable perovskite solar cell by modifying charge extraction, interfacial recombination losses, and band alignment. Here, cesium doped NiO_x is selected as a hole extraction layer to study the impact of Cs dopant on the optoelectronic properties of NiO_x and the photovoltaic performance. Cs doped NiO_x films are prepared by a simple solution‐based method. Both doped and undoped NiO_x films are smooth and highly transparent, while the Cs doped NiO_x exhibits better electron conductivity and higher work function. Therefore, Cs doping results in a significant improvement in the performance of NiO_x‐based inverted planar perovskite solar cells. The best efficiency of Cs doped NiO_x devices is 19.35%, and those devices show high stability as well. The improved efficiency in devices with Cs:NiO_x is attributed to a significant improvement in the hole extraction and better band alignment compared to undoped NiO_x. This work reveals that Cs doped NiO_x is very promising hole extraction material for high and stable inverted perovskite solar cells.     

Few‐Layer MoS2 Flakes as Active Buffer Layer for Stable Perovskite Solar Cells

Solution‐processed few‐layer MoS₂ flakes are exploited as an active buffer layer in hybrid lead–halide perovskite solar cells (PSCs). Glass/FTO/compact‐TiO₂/mesoporous‐TiO₂/CH₃NH₃PbI₃/MoS₂/Spiro‐OMeTAD/Au solar cells are realized with the MoS₂ flakes having a twofold function, acting both as a protective layer, by preventing the formation of shunt contacts between the perovskite and the Au electrode, and as a hole transport layer from the perovskite to the Spiro‐OMeTAD. As prepared PSC demonstrates a power conversion efficiency (η) of 13.3%, along with a higher lifetime stability over 550 h with respect to reference PSC without MoS₂ (Δη/η = ?7% vs. Δη/η = ?34%). Large‐area PSCs (1.05 cm² active area) are also fabricated to demonstrate the scalability of this approach, achieving η of 11.5%. Our results pave the way toward the implementation of MoS₂ as a material able to boost the shelf life of large‐area perovskite solar cells in view of their commercialization.     

Room‐Temperature Vapor Deposition of Cobalt Nitride Nanofilms for Mesoscopic and Perovskite Solar Cells

Organic/inorganic hybrid solar cells, typically mesoscopic and perovskite solar cells, are regarded as promising candidates to replace conventional silicon or thin film photovoltaics. There have been intensive investigations on the development of advanced materials for improved power conversion efficiencies, however, economical feasibilities and reliabilities of the organic/inorganic photovoltaics are yet to reach at a sufficient level for practical utilizations. In this study, cobalt nitride (CoN) nanofilms prepared by room‐temperature vapor deposition in an inert N₂ atmosphere, which is a facile and highly reproducible procedure, are proposed as a low‐cost counter electrode in mesoscopic dye‐sensitized solar cells (DSCs) and a hole transport material in inverted planar perovskite solar cells (PSCs) for the first time. The CoN film successfully replaces conventional Pt in DSCs, resulting in a power conversion efficiency comparable to the ones based on Pt. In addition, PSCs employing the CoN manifest high efficiency even up to 15.0%, which is comparable to state‐of‐the‐art performance in the cases of PSCs employing inorganic hole transporters. Furthermore, flexible solar cell applications of the CoN are performed in both mesoscopic and perovskite solar cells, verifying the advantages of the room‐temperature deposition process and feasibilities of the CoN nanofilms in various fields.