Yingzhi Jin

Ternary Ni−Co–Cu sulfides confined in a nanosheets array are constructed on 3D copper foam by in situ growth and an ion-exchange process. The as-prepared ternary metal sulfides demonstrate synergistic interaction in unique structures and diverse compositions, which endows the material with a great potential for applications in supercapacitors and solar steam generation.

Copper foam (CF)-supported 3D nanosheets array composed of ternary Ni−Co−Cu chalcogenides are prepared by a simple in situ formation process. Specifically, a highly electroactive Ni−Co binary sulfide in nanosheets is synthesized against the CF backbone, whereas the copper species migrate from the CF to the Ni−Co nanosheets, leading to the in situ formation of the ternary metallic sulfide (Ni−Co−Cu−S, NCCS). Due to the synergistic interaction of Ni, Co, and Cu sulfides confined in nanosheets, this NCCS material demonstrates good mechanical robustness, a large surface area, and enhanced electric conductivity. As a result, the NCCS exhibits a high specific capacitance (750 mF cm⁻² at 100 mA cm⁻²) with good cycling performance (97.14% after 10 000 cycles) when used as supercapacitor electrodes. In addition, the 3D porous hierarchical nanostructure of NCCS provides nanoconfined water molecule channels to achieve high-yield solar steam generation, delivering an enhanced evaporation rate of 2.48 kg m⁻² h⁻¹ under 1 sun irradiation.

Three structurally similar non‐fullerene acceptors with various outer side chains are designed and matched with a cost‐effective donor polymer named PTQ10 to fabricate organic solar cells. High efficiencies of 17.1% and 17.6% are achieved by the PTQ10‐based binary and ternary devices, respectively, demonstrating the significance of material compatibility in fine‐tuning morphology toward high‐performance organic photovoltaics.

Abstract

In this work, the properties and performance of three structurally similar non‐fullerene acceptors (named BTP‐Ph, BTP‐Th, and BTP‐C11) possessing different side chains on the β‐positions of the thienothiophene units of the Y6 molecule are systematically studied. The steric and electronic effects of these side chains on the blend morphology and device performance based on the PTQ10 donor polymer are investigated. It is found that the thiophene and benzene units on the side chains introduce more steric hindrance and thus slightly reduce the crystallinity of the molecule. However, an interesting matching trend with the PTQ10 donor that appears to better match with the less crystalline molecules is observed. Overall, PTQ10:BTP‐Ph delivers the highest performance of 17.1% due to the suitable phase separation among three blends. Next, a ternary strategy is explored by incorporating BTP‐Th/BTP‐C11 with better molecular packing into PTQ10:BTP‐Ph, which successfully extends photon response, enhances charge transport, and suppresses charge recombination compared with the binary blend. Due to these synergistic effects, the ternary device based on PTQ10:BTP‐Ph:BTP‐Th achieves an outstanding power conversion efficiency of 17.6% with a fill factor of 78.8%, which is the highest value of PTQ10‐based devices to date.

External quantum efficiency spectra are parameterized through the sigmoid function for reporting the bandgap energy (E _g) and the sigmoid wavelength range (λ_s), which quantify the steepness of the absorption onset. Large values of λ_s indicate significant photovoltage losses and produce particularly high short‐circuit currents for some ranges of E _g, regarding the Shockley–Queisser model.

Abstract

The external quantum efficiency (EQE), also known as incident‐photon‐to‐collected‐electron spectra are typically used to access the energy dependent photocurrent losses for photovoltaic devices. The integral over the EQE spectrum results in the theoretical short‐circuit current under a given incident illumination spectrum. Additionally, one can also estimate the photovoltaic bandgap energy (E _g) from the inflection point in the absorption threshold region. The latter has recently been implemented in the “Emerging PV reports,” where the highest power conversion efficiencies are listed for different application categories, as a function of E _g. Furthermore, the device performance is put into perspective thereby relating it to the corresponding theoretical limit in the Shockley–Queisser (SQ) model. Here, the evaluation of the EQE spectrum through the sigmoid function is discussed and proven to effectively report the E _g value and the sigmoid wavelength range λ_s, which quantifies the steepness of the absorption onset. It is also shown how EQE spectra with large λ_s indicate significant photovoltage losses and present the corresponding implications on the photocurrent SQ model. Similarly, the difference between the photovoltaic and optical bandgap is analyzed in terms of λ_s.

A novel naphtho[2,3‐b:6,7‐b′]difuran (NDF)‐based copolymer NDF‐3T is designed and applied in organic solar cells (OSCs). The champion device based on NDF‐3T/ ITIC‐4Cl shows a PCE of 14.21%, due to the favorable molecular conformational modulation. Importantly, 14.21% is the highest PCE reported for furan‐based single‐junction OSCs. Therefore, the NDF is shown to be a promising building block in organic electronic materials.

Abstract

As one kind of abundant product from renewable resources, furan and its fused‐ring derivatives, have provoked great interest in the context of developing efficient photovoltaic materials. However, the power conversion efficiency (PCE) of furan‐based photovoltaic materials has lagged behind its thiophene counterparts. In this work, in consideration of the ordered π–π stacking via extending conjugation to further improve the charge mobility, a novel furan fused‐ring derivative of naphtho[2,3‐b:6,7‐b′]difuran (NDF) based copolymer of NDF‐3T is designed and synthesized. Because of its favorable linear molecular conformation, the NDF‐3T possesses a high crystallinity, as well as ordered and dense π–π stacking. Subsequently, the NDF‐3T‐based device exhibits an efficient PCE of 14.21%, which is higher than that of the analogue naphthodithiophene (NDT) counterpart (10.86%). To the best of the authors’ knowledge, the PCE is also the best record in furan‐based photovoltaic materials. More importantly, the development of line NDF shows great potential in construing highly efficient photovoltaic materials and can be referenced to other furan fused‐ring structures.

The potential of wide bandgap perovskite solar cells is often limited by low open‐circuit voltages. By tuning the lowest‐unoccupied molecular‐orbital of electron transport layers via the use of different fullerenes and fullerene blends, open‐circuit voltages exceeding 1.35 V in CH₃NH₃Pb(I_0.8Br_0.2)₃ device without loss in fill factor leading to a high V _oc FF product of 1.10 V are demonstrated.

Abstract

Nonradiative recombination processes are the biggest hindrance to approaching the radiative limit of the open‐circuit voltage for wide bandgap perovskite solar cells. In addition to high bulk quality, good interfaces and good energy level alignment for majority carriers at charge transport layer‐absorber interfaces are crucial to minimize nonradiative recombination pathways. By tuning the lowest‐unoccupied molecular‐orbital of electron transport layers via the use of different fullerenes and fullerene blends, open‐circuit voltages exceeding 1.35 V in CH₃NH₃Pb(I_0.8Br_0.2)₃ device are demonstrated. Further optimization of mobility in binary fullerenes electron transport layers can boost the power conversion efficiency as high as 18.9%. It is noted in particular that the V _oc fill factor product is >1.096 V, which is the highest value reported for halide perovskites with this bandgap.

A novel IDTT‐based small molecule (SM) additive (IDTT‐ThCz) is developed and introduced into perovskite solar cells (PSCs) through an anti‐solvent engineering method. This IDTT‐ThCz passivates defect states of perovskite layers, providing efficient charge extraction as well as preventing the decomposition of perovskite crystals. Therefore, IDTT‐ThCz treated PSCs achieve a highest efficiency of 22.5% and remarkable thermal stability.

Abstract

Although perovskite solar cells (PSCs) have attracted enormous attention owing to their fascinating optoelectronic properties and solution processability, defects in PSCs, which adversely affect efficiency and stability, are still not completely resolved. Herein, a novel indacenodithieno[3,2‐b]thiophene‐based small molecule (SM) additive (IDTT‐ThCz), capable of interacting with perovskite layers, is developed. In particular, the IDTT‐ThCz, which can perform a surface passivation, is introduced into the perovskite layer to significantly suppress perovskite defects via antisolvent treatment. Furthermore, this facile surface passivation not only significantly improves the charge extraction capability, but also prevents perovskite degradation. The IDTT‐ThCz‐treated PSCs exhibits a power conversion efficiency (PCE) of 22.5% and retains 95% of its initial PCE after 500 h storage under thermal condition (85 °C), representing the most remarkable efficiency as well as stability among the SM additives reported to date.

Bottom-surface defect passivation of perovskite film is enabled by covalently attaching –OH to a hole-transporting polymer. A solvent evaporation-induced self-assembly of the resultant amphiphilic hole-transporting polymer enriches –OH on the film surface, passivating defects of the upper perovskite layer. Inverted perovskite solar cells based on this polymer afford an efficiency of 20.12% with improved device stability compared to its poly(bis(4-phenyl)(2,5,6-trimethylphenyl)amine) counterpart.

Abstract

Bottom-surface defect passivation of perovskite film, lagging far behind easily conducted bulk and top-surface passivations in perovskite solar cells (PSCs), remains rather challenging because most passivation molecules/groups can be eroded by polar solvents used for the subsequent perovskite deposition. In this work, an effective bottom-surface passivation is enabled for enhanced performance of inverted PSCs by covalently attaching a passivation group (hydroxyl) to a hole transporting polymer. A short linker (methylene) between the hydroxyl and the conjugated backbone bearing hydrophobic long alkyl chains is adopted to improve the resistance of the resultant amphiphilic polymer to polar solvents. A solvent evaporation-induced self-assembly of the amphiphilic hole transporting polymer is developed to enrich hydroxyl groups on the film surface, passivating defects of the upper perovskite layer via interactions with undercoordinated Pb²⁺ and I^– sites. Inverted PSCs based on this hole transporting film are superior in efficiency (20.12%), reproducibility, large-area fabrication, and stability to its classical poly(bis(4-phenyl)(2,5,6-trimethylphenyl)amine) counterpart. This work demonstrates that rational introduction of passivation groups into the hole transporting layer combined with self-assembly-modulated component distributions is useful to realize bottom-surface passivation of the perovskite layer for improved photovoltaic performance.

Room‐temperature high‐efficiency light‐emitting diodes based on metal halide perovskite FAPbI₃ can work perfectly at low temperatures. A peak external quantum efficiency of 32.8%, corresponding to an internal quantum efficiency of 100%, is achieved at 45 K. Importantly, the device shows almost no degradation after working at a constant current density of 200 mA m⁻² for 330 h.

Abstract

Room‐temperature‐high‐efficiency light‐emitting diodes based on metal halide perovskite FAPbI₃ are shown to be able to work perfectly at low temperatures. A peak external quantum efficiency (EQE) of 32.8%, corresponding to an internal quantum efficiency of 100%, is achieved at 45 K. Importantly, the devices show almost no degradation after working at a constant current density of 200 mA m⁻² for 330 h. The enhanced EQEs at low temperatures result from the increased photoluminescence quantum efficiencies of the perovskite, which is caused by the increased radiative recombination rate. Spectroscopic and calculation results suggest that the phase transitions of the FAPbI₃ play an important role for the enhancement of exciton binding energy, which increases the recombination rate.

Notable developments of SnO₂ as an electron‐selective layer for efficient perovskite solar cells (PSCs) are reviewed, along with an overview of the fabrication methods and interfacial passivation routes. Furthermore, techno‐economic and toxicology analyses of SnO₂ are discussed for possible large‐scale deployment of PSCs. Finally, the role of SnO₂ in scaled module and tandem solar cell production is revealed.

Abstract

Perovskite solar cells (PSCs) have become a promising photovoltaic (PV) technology, where the evolution of the electron‐selective layers (ESLs), an integral part of any PV device, has played a distinctive role to their progress. To date, the mesoporous titanium dioxide (TiO₂)/compact TiO₂ stack has been among the most used ESLs in state‐of‐the‐art PSCs. However, this material requires high‐temperature sintering and may induce hysteresis under operational conditions, raising concerns about its use toward commercialization. Recently, tin oxide (SnO₂) has emerged as an attractive alternative ESL, thanks to its wide bandgap, high optical transmission, high carrier mobility, suitable band alignment with perovskites, and decent chemical stability. Additionally, its low‐temperature processability enables compatibility with temperature‐sensitive substrates, and thus flexible devices and tandem solar cells. Here, the notable developments of SnO₂ as a perovskite‐relevant ESL are reviewed with emphasis placed on the various fabrication methods and interfacial passivation routes toward champion solar cells with high stability. Further, a techno‐economic analysis of SnO₂ materials for large‐scale deployment, together with a processing‐toxicology assessment, is presented. Finally, a perspective on how SnO₂ materials can be instrumental in successful large‐scale module and perovskite‐based tandem solar cell manufacturing is provided.

Owing to intramolecular charge transfer enhanced by cucurbit[8]uril, a supramolecular pin shows afterglow with high phosphorescence quantum yield (99.38%) after incorporation into a rigid matrix, which is the highest yield reported to date for phosphorescent materials. Moreover, supramolecular pins are applied for targeted phosphorescence imaging of mitochondria.

Abstract

Constructing ultralong organic phosphorescent materials possessing a high quantum yield is challenging. Herein, assemblies of purely organic supramolecular pins composed of alkyl‐bridged phenylpyridinium salts and cucurbit[8]uril (CB[8]) are reported. Different from “one host with two guests” and “head‐to‐tail” binding, the binding formation of supramolecular pins is “one host with one guest” and “head‐to‐head,” which overcomes electrostatic repulsion and promotes intramolecular charge transfer. The supramolecular pin 1/CB[8] displays afterglow with high phosphorescence quantum yield (99.38%) after incorporation into a rigid matrix, which is the highest yield reported to date for phosphorescent materials. Moreover, multicolor photoluminescence can be obtained by different excitation wavelengths and ratios of host to guest. Owing to the redshift of the absorption, the supramolecular pins are applied for targeted phosphorescence imaging of mitochondria. This work will provide a reasonable supramolecular strategy to achieve redshifted and efficient phosphorescence both in the solid state and in aqueous solution.

Thermodynamically stable β‐CsPbI₃ nanocrystals are prepared, and they are demonstrated to function as a stable, efficient red‐emitting layer. With incorporation of poly(maleic anhydride‐alt‐1‐octadecene), the β‐CsPbI₃ further exhibits reduced deep defects of Pb_Cs, increased exciton binding energy, and reduced longitudinal‐optical phonon energy. Red‐emitting perovskite light‐emitting diodes (PeLEDs) based on β‐CsPbI₃ achieve both high external quantum efficiency and superior operational stability.

Abstract

The long‐term operational stability of perovskite light‐emitting diodes (PeLEDs), especially red PeLEDs with only several hours typically, has always faced great challenges. Stable β‐CsPbI₃ nanocrystals (NCs) are demonstrated for highly efficient and stable red‐emitting PeLEDs through incorporation of poly(maleic anhydride‐alt‐1‐octadecene) (PMA) in synthesizing the NCs. The PMA can chemically interact with PbI₂ in the precursors via the coupling effect between O groups in PMA and Pb²⁺ to favor crystallization of stable β‐CsPbI₃ NCs. Meanwhile, the cross‐linked PMA significantly reduces the Pb_Cs anti‐site defect on the surface of the β‐CsPbI₃ NCs. Benefiting from the improved crystal phase quality, the photoluminescence quantum yield for β‐CsPbI₃ NCs films remarkably increases from 34% to 89%. The corresponding red‐emitting PeLEDs achieves a high external quantum efficiency of 17.8% and superior operational stability with the lifetime, the time to half the initial electroluminescence intensity (T ₅₀) reaching 317 h at a constant current density of 30 mA cm⁻².

Small‐molecule organic solar cells based on a new electron donor reach power conversion efficiencies exceeding 13% with and without the use of electrode interlayers, but differ strongly in stability. Surprisingly, the surface composition and morphology of the interlayers deteriorate with time even under inert conditions, reducing device performance. Without interlayers, the cells give stable high performance.

Abstract

Electron transport layers (ETLs) placed between the electrodes and a photoactive layer can enhance the performance of organic solar cells but also impose limitations. Most ETLs are ultrathin films, and their deposition can disturb the morphology of the photoactive layers, complicate device fabrication, raise cost, and also affect device stability. To fully overcome such drawbacks, efficient organic solar cells that operate without an ETL are preferred. In this study, a new small‐molecule electron donor (H31) based on a thiophene‐substituted benzodithiophene core unit with trialkylsilyl side chains is designed and synthesized. Blending H31 with the electron acceptor Y6 gives solar cells with power conversion efficiencies exceeding 13% with and without 2,9‐bis[3‐(dimethyloxidoamino)propyl]anthra[2,1,9‐def:6,5,10‐d′e′f ′]diisoquinoline‐1,3,8,10(2H,9H)‐tetrone (PDINO) as the ETL. The ETL‐free cells deliver a superior shelf life compared to devices with an ETL. Small‐molecule donor–acceptor blends thus provide interesting perspectives for achieving efficient, reproducible, and stable device architectures without electrode interlayers.

A facile strategy of employing an acceptor‐analogue is developed to efficiently reduce trap density to a magnitude of 10¹⁵ cm⁻³ for organic photovoltaic materials, which is comparable to and even lower than those of some inorganic counterparts, and boosts the power conversion efficiency of organic solar cells up to 17.8%.

Abstract

Typical organic semiconductor materials exhibit a high trap density of states, ranging from 10¹⁶ to 10¹⁸ cm⁻³, which is one of the important factors in limiting the improvement of power conversion efficiencies (PCEs) of organic solar cells (OSCs). In order to reduce the trap density within OSCs, a new strategy to design and synthesize an electron acceptor analogue, BTPR, is developed, which is introduced into OSCs as a third component to enhance the molecular packing order of electron acceptor with and without blending a polymer donor. Finally, the as‐cast ternary OSC devices employing BTPR show a notable PCE of 17.8%, with a low trap density (10¹⁵ cm⁻³) and a low energy loss (0.217 eV) caused by non‐radiative recombination. This PCE is among the highest values for single‐junction OSCs. The trap density of OSCs with the BTPR additives, as low as 10¹⁵ cm⁻³, is comparable to and even lower than those of several typical high‐performance inorganic/hybrid counterparts, like 10¹⁶ cm⁻³ for amorphous silicon, 10¹⁶ cm⁻³ for metal oxides, and 10¹⁴ to 10¹⁵ cm⁻³ for halide perovskite thin film, and makes it promising for OSCs to obtain a PCE of up to 20%.

Combining the layer‐by‐layer processing method and a ternary strategy, 18.16% efficiency, which is among the highest values reported to date, is achieved in single‐junction organic photovoltaics (OPVs) based on the PM6:BO‐4Cl:BTP‐S2 blend, superior to that (18.03%) of bulk‐heterojunction OPVs, proving that layer‐by‐layer processed ternary OPVs could be a promising approach to high efficiencies.

Abstract

Obtaining a finely tuned morphology of the active layer to facilitate both charge generation and charge extraction has long been the goal in the field of organic photovoltaics (OPVs). Here, a solution to resolve the above challenge via synergistically combining the layer‐by‐layer (LbL) procedure and the ternary strategy is proposed and demonstrated. By adding an asymmetric electron acceptor, BTP‐S2, with lower miscibility to the binary donor:acceptor host of PM6:BO‐4Cl, vertical phase distribution can be formed with donor‐enrichment at the anode and acceptor‐enrichment at the cathode in OPV devices during the LbL processing. In contrast, LbL‐type binary OPVs based on PM6:BO‐4Cl still show bulk‐heterojunction like morphology. The formation of the vertical phase distribution can not only reduce charge recombination but also promote charge collection, thus enhancing the photocurrent and fill factor in LbL‐type ternary OPVs. Consequently, LbL‐type ternary OPVs exhibit the best efficiency of 18.16% (certified: 17.8%), which is among the highest values reported to date for OPVs. The work provides a facile and effective approach for achieving high‐efficiency OPVs with expected morphologies, and demonstrates the LbL‐type ternary strategy as being a promising procedure in fabricating OPV devices from the present laboratory study to future industrial production.

A thermally stable perovskite solar cell is developed by capturing mobile lithium ions using a new molecular hole transporter, 1,3‐bis(5‐(4‐(bis(4‐methoxyphenyl)amino)phenyl)thieno[3,2‐b]thiophen‐2‐yl)‐5‐octyl‐4H‐thieno[3,4‐c]pyrrole‐4,6(5H)‐dione (coded HL38), where a strong interaction of the lithium ions in lithium bis(trifluoromethanesulfonyl)imide with the 5‐octylthieno[3,4‐c]pyrrole‐4,6‐dione (octyl‐TPD) moiety in HL38 is responsible for maintaining ≈86% of the initial power conversion efficiency for over 1000 h at 85 °C.

Abstract

A thermally stable perovskite solar cell (PSC) based on a new molecular hole transporter (MHT) of 1,3‐bis(5‐(4‐(bis(4‐methoxyphenyl) amino)phenyl)thieno[3,2‐b]thiophen‐2‐yl)‐5‐octyl‐4H‐thieno[3,4‐c]pyrrole‐4,6(5H)‐dione (coded HL38) is reported. Hole mobility of 1.36 × 10⁻³ cm² V⁻¹ s⁻¹ and glass transition temperature of 92.2 °C are determined for the HL38 doped with lithium bis(trifluoromethanesulfonyl)imide and 4‐tert‐butylpyridine as additives. Interface engineering with 2‐(2‐aminoethyl)thiophene hydroiodide (2‐TEAI) between the perovskite and the HL38 improves the power conversion efficiency (PCE) from 19.60% (untreated) to 21.98%, and this champion PCE is even higher than that of the additive‐containing 2,2′,7,7′‐tetrakis(N,N‐di‐p‐methoxyphenylamine)‐9,9′‐spirobifluorene (spiro‐MeOTAD)‐based device (21.15%). Thermal stability testing at 85 °C for over 1000 h shows that the HL38‐based PSC retains 85.9% of the initial PCE, while the spiro‐MeOTAD‐based PSC degrades unrecoverably from 21.1% to 5.8%. Time‐of‐flight secondary‐ion mass spectrometry studies combined with Fourier transform infrared spectroscopy reveal that HL38 shows lower lithium ion diffusivity than spiro‐MeOTAD due to a strong complexation of the Li⁺ with HL38, which is responsible for the higher degree of thermal stability. This work delivers an important message that capturing mobile Li⁺ in a hole‐transporting layer is critical in designing novel MHTs for improving the thermal stability of PSCs. In addition, it also highlights the impact of interface design on non‐conventional MHTs.

Conjugated D–A polymers with two types of azo groups, for which trans–cis isomerization can sequentially occur with light irradiation at different wavelengths, in the side chains possess tri‐stable semiconducting states. As a consequence, the performance of the resulting field‐effect transistors can be logically controlled by light irradiation at three different wavelengths, mimicking three‐value logic gates.

Abstract

A new design strategy for photoresponsive semiconducting polymer with tri‐stable semiconducting states is reported by simultaneous incorporation of tetra‐ortho‐methoxy‐substituted azobenzene (mAzo) and arylazopyrazole (pAzo) in the side chains. The trans‐to‐cis transformations for mAzo and pAzo groups can sequentially occur within the polymer thin film after sequential 560 and 365 nm light irradiation. Remarkably, the trans–cis isomerization of mAzo and pAzo groups can modulate the thin film crystallinity. Accordingly, the performances of the resulting field‐effect transistors (FETs) can be reversibly modulated, leading to tri‐stable semiconducting states after sequential 560, 365, and 470 nm light irradiation. Therefore, the device performance can be logically controlled by light irradiation at three different wavelengths. In addition, with light irradiation and device current as the input and output signals, the three‐value logic gate by using single FET device can be successfully mimicked.

Molecular vibrations govern the charge transport in organic semiconductors, which is limited by different sources of disorder. Understanding and mastering the disorder in these materials can drive the design of better semiconductors featuring band‐like transport.

Abstract

Charge transport in organic semiconductors is notoriously extremely sensitive to the presence of disorder, both internal and external (i.e., related to interactions with the dielectric layer), especially for n‐type materials. Internal dynamic disorder stems from large thermal fluctuations both in intermolecular transfer integrals and (molecular) site energies in weakly interacting van der Waals solids and sources transient localization of the charge carriers. The molecular vibrations that drive transient localization typically operate at low‐frequency (<a‐few‐hundred cm⁻¹), which makes it difficult to assess them experimentally. Hitherto, this has prevented the identification of clear molecular design rules to control and reduce dynamic disorder. In addition, the disorder can also be external, being controlled by the gate insulator dielectric properties. Here a comprehensive study of charge transport in two closely related n‐type molecular organic semiconductors using a combination of temperature‐dependent inelastic neutron scattering and photoelectron spectroscopy corroborated by electrical measurements, theory, and simulations is reported. Unambiguous evidence that ad hoc molecular design enables the electron charge carriers to be freed from both internal and external disorder to ultimately reach band‐like electron transport is provided.

A charge‐transfer complex strategy to reduce the energy disorder of organic semiconductor (OS) charge transport layers (CTLs) by doping a well‐designed OS (BDT‐Si) with electron‐acceptor features in a commercial hole‐transport material (PTAA) is proposed. As a result, the p–i–n planar perovskite solar cells with the optimized hole‐transport layer exhibit the best power conversion efficiency of 21.87%, and good operating stability at maximum power point under continuous illumination.

Abstract

Solution‐processed organic semiconductor charge‐transport layers (OS‐CTLs) with high mobility, low trap density, and energy level alignment have dominated the important progress in p–i–n planar perovskite solar cells (pero‐SCs). Unfortunately, their inevitable long chains result in weak molecular stacking, which is likely to generate high energy disorder and deteriorate the charge‐transport ability of OS‐CTLs. Here, a charge‐transfer complex (CTC) strategy to reduce the energy disorder in the OS‐CTLs by doping an organic semiconductor, 4,4′‐(4,8‐bis(5‐(trimethylsilyl)thiophen‐2‐yl)benzo[1,2‐b:4,5‐b′]dithiophene‐2,6‐diyl)bis(N,N‐bis(4‐methoxyphenyl)aniline) (BDT‐Si), in a commercial hole‐transport layer (HTL), poly[bis(4‐phenyl) (2,4,6‐trimethylphenyl)amine (PTAA), is proposed. The formation of the CTC makes the PTAA conjugated backbone electron‐deficient, resulting in a quinoidal and stiffer character, which is likely to planarize the PTAA backbone and enhance the ordering of the film in nanoscale. The resultant HTL exhibits a reduced energy disorder, which simultaneously promotes hole transport in the HTL, hole extraction at the interface, energy level alignment, and quasi‐Fermi level splitting in the device. As a result, the p–i–n planar pero‐SCs with optimized HTL exhibit the best power conversion efficiency of 21.87% with good operating stability. This finding demonstrates that the CTC strategy is an effective way to reduce the energy disorder in HTLs and to improve the performance of planar pero‐SCs.