Chen Weijie

Herein, a series of organic spacer cations with different alkyl chain lengths are introduced onto the three-dimensional perovskite to investigate the chain length effect. It's found that the chain length affects the quality of as-casted two-dimensional perovskite, leading to distinct effects on passivation and charge transfer properties.

While interface modification based on organic spacer cations has been proven to be a viable strategy to boost the performance of 3D perovskite solar cells, the mechanisms behind the accomplished efficiency enhancement and the selection rule for organic spacers are yet to be clarified. Herein, based on representative four ammonium halide salts featuring different chain lengths as spacer cations for the 2D perovskite surface modifier, it is shown that choosing appropriately sized spacers can lead to synergetic mediation on interfacial passivation of point and structural defects and the crystallization of 2D perovskite components in protecting the buried 3D perovskite film. As a result, promoted charge transport and extraction with suppressed charge trapping and recombination are simultaneously realized in the 3D/2D perovskite solar cells. With the optimal spacer cation phenylpropylammonium iodide (PPAI), the resultant 3D/2D devices produce a power conversion efficiency of 22.57% with a fill factor exceeding 0.8. Favorably, the PPAI-treated devices exhibit considerable gains in stability under various external stresses.

(CsFA)PbI_3–x Br _x film is in situ formed atop CsPbI_2.2Br_0.8 perovskite via a facile formamidinium iodide posttreatment method, which can broaden the light absorption range of CsPbI_2.2Br_0.8 and accelerate hole extraction from CsPbI_2.2Br_0.8 to the carbon electrode, thus greatly boosting the efficiency of a hole transporting layer-free carbon-based perovskite solar cell to 15.03% with an ultrahigh fill factor of 0.81.

Hole transporting layer (HTL)-free, all-inorganic CsPbX₃ (X: I, Br, or mixed halides), carbon-based perovskite solar cells (C-PSCs) show promising prospect for photovoltaic application due to their low cost, excellent stability, and theoretical high efficiency. However, the inefficient hole extraction of the carbon electrode and relatively narrow light absorption range of inorganic perovskite limit the power conversion efficiency (PCE) of this kind of PSCs. Herein, these issues are addressed through in situ constructing of an intermediate energy-level perovskite transition layer between CsPbI_2.2Br_0.8 and the carbon electrode via a facile formamidinium iodide (FAI) posttreatment strategy. It is demonstrated that the (CsFA)PbI_3–x Br _x film is in situ formed atop inorganic perovskite due to the ions exchange between FAI and CsPbI_2.2Br_0.8, which can not only broaden the light absorption edge of CsPbI_2.2Br_0.8 from 657 to 680 nm, but also serve as a hole transfer highway between CsPbI_2.2Br_0.8 and the carbon electrode, mainly due to its suitable intermediate energy-level and effective defect passivation. Consequently, the optimized HTL-free C-PSC achieves a champion PCE of 15.03% with an ultrahigh fill factor of 0.81. Besides, the stability of CsPbI_2.2Br_0.8 film (especially under humid environment) and corresponding C-PSC are also improved.

Herein, the advancements of the pure formamidinium (FA) and FA-rich perovskite solar cells (PSCs) with efficiencies exceeding 23% from the viewpoints of composition engineering, solvent engineering, additive engineering, and interface engineering are discussed. Further improvement in voltage and fill factor for the FA-based PSCs is expected to be able to achieve an efficiency over 30%.

To further improve power conversion efficiency (PCE) toward Shockley−Queisser limit efficiency approaching 32% for a single-junction perovskite solar cell (PSC) based on a lead halide perovskite with a bandgap of about 1.45 eV, it is important to improve the open-circuit voltage and fill factor (FF) significantly without sacrificing short-circuit current density. Herein, the advancements of the formamidinium-rich PSCs with PCEs exceeding 23% from the viewpoints of composition engineering, solvent engineering, additive engineering, and interface engineering are summarized and discussed. Based on the lessons, the possible strategies, methods, and research directions are proposed to further improve voltage and FF for ideal PCEs.

Emerging metallic nanomaterials including metal nanowires, metal meshes, and metal films are highly attractive for future flexible photovoltaics as bendable transparent electrodes. Herein, their material classifications, measurement/design considerations, and recent progress in flexible organic and perovskite solar cells are reviewed.

The rapid development of smart and wearable electronics calls for revolutionizing optoelectronics to become flexible, lightweight, and affordable. To meet these demands in photovoltaic devices, that is, solar cells, it is essential to develop mechanically flexible transparent electrodes over the conventional rigid ones while features such as low-temperature procedures, stability, solution process, and/or low cost are highly desired and often required. Moreover, the optoelectronic properties of an electrode must not be compromised in an operational flexible cell. Despite the considerable challenges, various bendable transparent electrodes for solar cells have emerged in recent years. Particularly, transparent electrodes based on metallic materials are especially attractive as metal offers excellent conductivity and their formation processing is generally mature and commercially viable. This work aims to provide an overview of the recent development of metal-based transparent electrodes for flexible organic and perovskite photovoltaics. After the introduction, metallic materials for the transparent electrodes including nanowires, meshes/grids, and films are discussed. The procedures and protocols for cell flexibility testing are summarized, before highlighting recent progress on fully functional, high-efficiency flexible organic and perovskite solar cells using these transparent metallic electrodes. Finally, the challenges and outlook of the research field are discussed.

C₆H₇NO and C₆H₆FNO additives are first doped into FA_0.75MA_0.25SnI₃ precursors and induce conspicuous increases in power conversion efficiency and stability in FA_0.75MA_0.25SnI₃ perovskite solar cells. The C₆H₆FNO additive with a fluorinated group has a low surface energy, which causes spontaneous migration of themselves to solution–air surface during the spin-coating process and then resulting in more expected initial crystal nucleation and growth from surface.

Stability and efficiency issues are closely related with poor perovskite film quality in perovskite solar cells (PSCs). Herein, 2-aminophenol (C₆H₇NO) and 2-amino-4-fluorophenol (C₆H₆FNO) are introduced to improve film quality of FA_0.75MA_0.25SnI₃, both of which consist of —NH₂ and —OH groups, and the latter also contains —F group. The experimental and theoretical analyses show both —NH₂ and —OH groups interact with I of the SnI₆ ⁴⁻ octahedron via hydrogen bond and fluorinated group with low surface energy causes spontaneous migration of C₆H₆FNO to solution–air surface and induces initial crystal nucleation and growth from surface, both of which contribute to improved film morphology and crystallinity and suppressed Sn²⁺ oxidation via reducing defect-state density and nonradiative recombination. The F atom of C₆H₆FNO facing outward protects FA_0.75MA_0.25SnI₃ from water penetration due to its hydrophobic feature. The C₆H₆FNO-doped PSC acquires a champion efficiency of 9.50% and a long-term stability of >800 h (80% efficiency remained in N₂).

New starburst molecules, bearing the carbazole moiety both as a central core and as peripheral groups, are synthesized and evaluated as hole transporting materials for perovskite solar cells. Their power conversion efficiencies range from 16.3% to 19.0%. Compounds bearing short aliphatic chains show exceptionally high glass transition temperatures, resulting in superior thermal stability compared with that of spiro-OMeTAD.

Five new star-shaped carbazole-based molecules are successfully synthesized from low-cost, commercially available reagents via a simple one-step synthesis route. All carbazole derivatives comprise a 3,6-diaminocarbazole core with carbazole peripheral groups substituted at the 2- or 3-positions and various aliphatic side chains. These molecules are evaluated as hole transporting materials to replace 2,2′,7,7′-tetrakis-(N,N-di-p-methoxyphenylamine)-9,9′-spirobifluorene (spiro-OMeTAD) in perovskite solar cells. Power conversion efficiencies of the devices with these carbazole hole transporting layers reach 19.0%, comparable with 19.7% obtained with the spiro-OMeTAD-based device. The thermal and operational stability of the candidate molecules are found to depend on the side chain substituents. Two candidate molecules with ethyl side chains show superior thermal stability compared with that of the reference solar cells prepared with spiro-OMeTAD.

Aiming to the application of power-generating windows, semitransparent organic solar cells (STOSCs) with ternary strategy are demonstrated. The third component not only assists to achieve proper film morphology for better optical properties, but also suppresses the recombination in devices. The best performing ternary STOSCs achieve power conversion efficiency (PCE) of 13.19% (Opaque 17.02%) with average visible transmittance (AVT) of 24.56%.

Semitransparent organic solar cells (STOSCs) make the industrialization of power-generating windows a reality with promising average visible transmittance (AVT) and rapidly increased power conversion efficiencies (PCEs). To achieve the ultimate goal, improving the efficiency of STOSCs without degrading the transparency in visible range is critical. Herein, a nonfused ring acceptor (BDC-4F-C8) by alkyl chain engineering is used as third component for ternary blend active layer to enhance the electrical and optical properties of STOSCs. With optimizing the proportion of third component, STOSCs with ternary active layer exhibit improved open-circuit voltage, short-circuit current, and fill factor, which leads to the best PCE of 13.19% with AVT of 24.56%, while the PCE of opaque one is 17.02%. This work presents an effective strategy to achieve high-performance ternary STOSCs with high AVT employing a low-cost nonfused ring electron acceptor material, and manifests how the third component affects the optical features of a ternary active layer to achieve efficient semitransparent devices.

An electron-withdrawing PZ-T unit is employed to incorporate into the PM6 polymer backbone as the third component, and a series of high-performance D-A₁-D-A₂ type terpolymers are synthesized by random copolymerization strategy. Among them, the PMZ-10:Y6-based polymer solar cells (PSCs) achieved an outstanding power conversion efficiency of 18.23%, which is the highest reported performance among the terpolymer-based PSCs so far.

Abstract

Recently, a random ternary copolymerization strategy has become a promising and efficient approach to develop high-performance polymer donors for polymer solar cells (PSCs). In this study, a low-cost electron-withdrawing unit, 2,5-bis(4-(2-ethylhexyl)thiophen-2-yl)pyrazine (PZ-T), is incorporated into the polymer backbone of PM6 as the third component, and three D-A₁-D-A₂ type terpolymers PMZ-10, PMZ-20, and PMZ-30 are synthesized by the random copolymerization strategy, with the PZ-T proportion of 10%, 20%, and 30%, respectively. The terpolymers exhibit downshifted highest occupied molecular orbital energy levels than PM6, which is beneficial for obtaining higher open-circuit voltage (V _oc) of the PSCs with the polymer as a donor. Importantly, the PSCs based on PMZ-10:Y6 demonstrate efficient exciton dissociation, higher and balanced electron/hole mobilities, desirable aggregation, and high power conversion efficiency of 18.23%, which is the highest efficiency among the terpolymer-based PSCs so far. The results indicate that the ternary copolymerization strategy with PZ-T as the second A-unit is an efficient approach to further improve the photovoltaic performance and reduce the synthetic cost of the D-A copolymer donors.

An effective light-deflecting pattern is introduced to nonfullerene organic solar cells to improve energy conversion efficiency in the blue region. The normal incidence light is guided into a cavity-like chamber and mostly captured by the active layer, resulting in broadband absorption enhancement. The optimized device based on all A-D-A type nonfullerene acceptors achieves the highest reported efficiency of approaching 18%.

Abstract

Using narrow bandgap nonfullerene acceptors (NFAs) can broaden the absorption spectrum of organic solar cells (OSCs) to the near-infrared region. However, the simultaneously decreased extinction coefficient of the active layer at the blue region results in inevitable light escaping and energy loss. Herein, a blazed grating-based device configuration consisting of a patterned rear electrode is employed to compensate for the low absorption of nonfullerene OSCs. Experimental results reveal that the normal incidence light, especially blue light, that bounces off the patterned rear electrode is concentrated in a large tilted angle and subsequently trapped in waveguide mode. Along with the excitation of surface plasmon polariton, the structured nonfullerene OSCs using a new-designed PM6:M36 active layer obtain the broadband absorption enhancement with 1.5 times increase at the blue region. The optimized device achieves an 8.95% increase in photocurrent and a champion power conversion efficiency of approaching 18%, which is the highest reported value among all the devices based on A-D-A type NFAs.

By introducing a dipole layer at the indium tin oxide/perovskite interface of the electron transport layer-free devices, with an efficient quantum tunneling effect, a quasi-ohmic contact of the front interface is realized. As a result, the device changes from a metal-semiconductor/PN cascade heterojunction solar cell to a single PN junction solar cell, and the corresponding ideal factor is reduced from 3.35 to 2.05.

Abstract

The pursuit of high power conversion efficiency (PCE) and cost-effective perovskite solar cells (PSCs) has spawned many innovative device structure designs. Compared with the traditional NIP type PSCs, electron transport layer (ETL) free PSCs have attracted growing attention due to their enormous potential in large area, low-cost flexible application. However, there is still a lack of in-depth understanding of the energy level arrangement indium tin oxide (ITO)/perovskite interface, resulting in poor device performance. Here, a metal/insulator/n-type perovskite/p-type spiro-MeOTAD (MINP) structure is proposed to elaborate on the influence of the apparent work function and contact barrier change of the metal–semiconductor (MS) and metal–insulator–semiconductor (MIS) junction on the carrier transfer and collection. Common and easily available 5-amino-valeric acid is inserted into the ITO/perovskite interface to form an insulating dipole layer and to ensure quasi-ohmic contact at the front interface. Consequently, the device changes from Schottky/PN cascade heterojunction type to a single PN heterojunction device with its ideal factor decreasing from 3.35 to 2.05. Accordingly, the champion device achieves 19.37% PCE with significantly increased V _oc and FF compared to the pristine device. This work provides a facile and effective method to improve the application potential of novel ETL-free PSCs.

Nonionic cross-linked 1D PbI₂-DPPO located at perovskite grain boundaries can passivate the defects and suppress the ion migration in 3D perovskites, thus significantly improving the intrinsic stability of perovskite films. Consequently, a 1D-PbI₂/3D heterojunction perovskite solar cells mini-module demonstrates a certified stabilized power conversion efficiency of 17.8% and superior long-term stability.

Abstract

Long-term stability has become the major obstacle for the successful large-scale application of perovskites devices. Owing to the ionic nature of metal-halide perovskites, the interfacial ion diffusion can induce irreversible degradation under operational conditions, which presents a great challenge to realize stable perovskite solar modules. Here, a diphenylphosphine oxide compound, ethane-1,2-diylbis(diphenylphosphine oxide) (DPPO) is introduced to coordinate with lead iodide and form a cross-linked 1D Pb₃I₆-DPPO (1D-PbI₂) complex. These judiciously designed cross-linked nonionic low-dimensional lead halide/organic adducts can passivate the defects of perovskite while acting as a robust ion diffusion barrier, thus significantly improving the electronic quality and intrinsic stability of perovskite films. As a result, high-performance inverted (p-i-n) solar modules with a champion efficiency approaching 19% (a certified stabilized efficiency of 17.8%) for active device areas above 17 cm² without the use of antisolvents, accompanied by outstanding operational stability under heat stress and continuous illumination are achieved.

A 10.7% -efficiency Sb₂(S,Se)₃ solar cell is achieved by a solution post-treatment technique, which regulates the energy band alignment and reduces the mismatch of the valence bands between the absorber and hole transport layer.

Abstract

Continuously boosting the power conversion efficiency (PCE) and delving deeper into its functionalities are essential problems faced by the very new antimony selenosulfide (Sb₂(S,Se)₃) solar technology. Here, a convenient and effective solution post-treatment (SPT) technique is used to fabricate high-performance Sb₂(S,Se)₃ solar cells, where alkali metal fluorides are applied to improve the quality of Sb₂(S,Se)₃ films in terms of morphology, crystallinity, and conductivity. In particular, this approach is able to manipulate the S/Se gradient in the films and creates favorable energy alignment which facilitates the carrier transport. As a result, the fill factor and short-circuit current density of Sb₂(S,Se)₃ solar cells (Glass/FTO/Zn(O,S)/CdS/Sb₂(S,Se)₃/Spiro-OMeTAD/Au) based on the SPT strategy are significantly enhanced, achieving a champion efficiency of 10.7%. To date, this conversion efficiency value represents the highest efficiency of all Sb-based solar cells. This study provides an effective post-treatment strategy for improving the quality of Sb₂(S,Se)₃ film which sheds new light on the fabrication of high-efficiency Sb₂(S,Se)₃ solar cells.

The similarities and differences in the charge carrier dynamics in organic solar cells and organic–inorganic hybrid metal halide perovskite solar cells, two leading technologies in thin-film photovoltaics, are discussed, linking these back to the intrinsic material properties of organic and perovskite semiconductors, and how these factors impact on photovoltaic device performance is elucidated.

Abstract

The charge carrier dynamics in organic solar cells and organic–inorganic hybrid metal halide perovskite solar cells, two leading technologies in thin-film photovoltaics, are compared. The similarities and differences in charge generation, charge separation, charge transport, charge collection, and charge recombination in these two technologies are discussed, linking these back to the intrinsic material properties of organic and perovskite semiconductors, and how these factors impact on photovoltaic device performance is elucidated. In particular, the impact of exciton binding energy, charge transfer states, bimolecular recombination, charge carrier transport, sub-bandgap tail states, and surface recombination is evaluated, and the lessons learned from transient optical and optoelectronic measurements are discussed. This perspective thus highlights the key factors limiting device performance and rationalizes similarities and differences in design requirements between organic and perovskite solar cells.

Two novel small-molecule donors with thioalkyl chains in the para- (P-PhS) and the meta-position (M-PhS) are synthesized to regulate surface tension and molecular packing. An optimized morphology with small domains and ordered packing is simultanously obtained in the M-PhS:BTP-eC9 blend, promoting a record power conversion efficiency (PCE) of 16.2% with excellent (FF × J _sc) in all-small-molecule organic solar cells (ASM-OSCs).

Abstract

In all-small-molecule organic solar cells (ASM-OSCs), a high short-circuit current (J _sc) usually needs a small phase separation, while a high fill factor (FF) is generally realized in a highly ordered packing system. However, small domain and ordered packing always conflicted each other in ASM-OSCs, leading to a mutually restricted J _sc and FF. In this study, alleviation of the previous dilemma by the strategy of obtaining simultaneous good miscibility and ordered packing through modulating homo- and heteromolecular interactions is proposed. By moving the alkyl-thiolation side chains from the para- to the meta-position in the small-molecule donor, the surface tension and molecular planarity are synchronously enhanced, resulting in compatible properties of good miscibility with acceptor BTP-eC9 and strong self-assembly ability. As a result, an optimized morphology with multi-length-scale domains and highly ordered packing is realized. The device exhibits a long carrier lifetime (39.8 μs) and fast charge collection (15.5 ns). A record efficiency of 16.2% with a high FF of 75.6% and a J _sc of 25.4 mA cm⁻² in the ASM-OSCs is obtained. These results demonstrate that the strategy of simultaneously obtaining good miscibility with high crystallinity could be an efficient photovoltaic material design principle for high-performance ASM-OSCs.

Three D–D type wide-bandgap donor polymers (PBDTT, PBDTT1Cl, and PBDTT2Cl) are designed and facilely synthesized. Organic solar cells (OSCs) based on PBDTT1Cl exhibit a high power conversion efficiency of 17% and a low nonradiative energy loss of 0.19 eV. In addition, PBDTT1Cl has a very low figure-of-merit and good universality, indicating its potential as a low-cost polymer donor for high-performance OSCs.

Abstract

Three regioregular benzodithiophene-based donor–donor (D–D)-type polymers (PBDTT, PBDTT1Cl, and PBDTT2Cl) are designed, synthesized, and used as donor materials in organic solar cells (OSCs). Because of the weak intramolecular charge-transfer effect, these polymers exhibit large optical bandgaps (>2.0 eV). Among these three polymers, PBDTT1Cl exhibits more ordered and closer molecular stacking, and its devices demonstrate higher and more balanced charge mobilities and a longer charge-separated state lifetime. As a result of these comprehensive benefits, PBDTT1Cl-based OSCs give a very impressive power conversion efficiency (PCE) of 17.10% with a low nonradiative energy loss (0.19 eV). Moreover, PBDTT1Cl also possesses a low figure-of-merit value and good universality to match with different acceptors. This work provides a simply and efficient strategy to design low-cost high-performance polymer donor materials.

In this work, the flexible monovalent spacer cations are introduced into the formamidinium-based low-dimensional perovskite, which effectively alleviates lattice distortion and reduce crystal defects. The resultant perovskite films possess desirable microscopic morphology, preferable crystal orientation, reduced defect states, and improved charge transport capability, which delivers highly efficient and thermostable perovskite solar cells.

Abstract

2D Dion–Jacobson (DJ) perovskite solar cells generally show mediocre device performances as they are restrained by their defective film quality. The rigid diammonium organic interlayer spacers are intolerant to lattice mismatches, which induces defects and distortions and ultimately deteriorates the optoelectronic properties. Herein, a secondary interlayer spacer is introduced into formamidinium (FA)-based low-dimensional perovskite, which substantially improves the film quality. The flexible monovalent spacer cations effectively alleviate lattice distortions and reduce crystal defects, providing perovskite films with desirable microscopic morphology, preferable crystal orientation, reduced defect states, and improved charge transport capability. As a result, the optimized perovskite solar cell based on the (PDA_0.9PA_0.2)(FA)₃Pb₄I₁₃ (PDA = propane-1,3-diammonium, PA = propylammonium) film exhibits the exceptional power conversion efficiency of 16.0%, the highest reported value in its class. In addition, the device demonstrates the enhanced thermal stability, retaining 90% of its initial efficiency after aging at 85 °C for 800 h.

Dion–Jacobson (DJ) and alternating-cation-interlayer (ACI) phases are two emerging types of layered 2D halide perovskites with high potential in balanced charge-transport properties and chemical stability. By tailoring the molecular, thin-film, and device chemistries, high-performance solar cells have been demonstrated.

Abstract

Layered halide perovskites (LHPs) with crystallographically 2D structures have gained increasing interest for photovoltaic applications due to their superior chemical stability and intriguing anisotropic properties, which are in contrast to their conventional 3D perovskite counterparts. The most frequently studied LHPs are Ruddlesden–Popper (RP) phases, which suffer from a carrier-transport bottleneck due to the van der Waals gap associated with their intrinsic organic interlayer structures. To address this issue, Dion–Jacobson (DJ) and alternating-cation-interlayer (ACI) LHPs have rapidly emerged, which exhibit unique structural and (opto)electronic characteristics that may resemble those of the 3D counterparts owing to the eliminated or reduced van der Waals gap. Improved photophysical properties have been achieved in DJ and ACI LHPs, leading towards better photovoltaic performance. Here we provide a comprehensive discussion on the merits and promises of DJ and ACI LHPs from a chemistry perspective. Then, we review recent progress on the synthesis and tailoring of DJ and ACI LHP crystals and thin films, as well as their optoelectronic properties and photovoltaic performance. Finally, we discuss possible pathways to overcome critical challenges to realize the full potential of DJ and ACI LHPs for high-performance solar cells and beyond.

Nature Photonics, Published online: 27 October 2021; doi:10.1038/s41566-021-00898-5

Nature Photonics, Published online: 27 October 2021; doi:10.1038/s41566-021-00905-9

Nature Energy, Published online: 01 November 2021; doi:10.1038/s41560-021-00923-5

Publication date: 10 January 2022

Source: Electrochimica Acta, Volume 402

Author(s): Mohamad Firdaus Mohamad Noh, Nurul Affiqah Arzaee, Inzamam Nawas Nawas Mumthas, Amin Aadenan, Hussain Alessa, Mohammed N. Alghamdi, Hazim Moria, Nurul Aida Mohamed, Abd Rashid Bin Mohd Yusoff, Mohd Asri Mat Teridi

Perovskite surface treatment by homologous bromide salts is investigated. It is found that bromides not only passivate surface defects but also penetrate into the perovskite providing bulk passivation. This leads to a large voltage of 1.24 V in a 1.63 eV bandgap device and an efficiency of 23.7% in a 1.56 eV bandgap device.

Abstract

The power conversion efficiency (PCE) of solution-processed organic–inorganic mixed halide perovskite solar cells has achieved rapid improvement. However, it is imperative to minimize the voltage deficit (W _oc = E _g/q − V _oc) for their PCE to approach the theoretical limit. Herein, the strategy of depositing homologous bromide salts on the perovskite surface to achieve a surface and bulk passivation for the fabrication of solar cells with high open-circuit voltage is reported. Distinct from the conclusions given by previous works, that homologous bromides such as FABr only react with PbI₂ to form a large-bandgap perovskite layer on top of the original perovskite, this work shows that the bromide also penetrates the perovskite film and passivates the perovskite in the bulk. This is confirmed by the small-bandgap enlargement observed by absorbance and photoluminescence, and the bromide element ratio increasing in the bulk by time-of-flight secondary-ion mass spectrometry and depth-resolved X-ray photoelectron spectroscopy. Furthermore, a clear suppression of non-radiative recombination is confirmed by a variety of characterization methods. This work provides a simple and universal way to reduce the W _oc of single-junction perovskite solar cells and it will also shed light on developing other high-performance optoelectronic devices, including perovskite-based tandems and light-emitting diodes.

High-efficiency ternary organic solar cells are fabricated using two nonfullerene acceptors DO-2F, IDTT-OB and one polymer donor PBDB-T. The introduction of IDTT-OB into PBDB-T:DO-2F can effectively optimize blend film morphology, improve charge dissociation and extraction, and suppress bimolecular recombination and nonradiative energy loss. The PBDB-T:DO-2F:IDTT-OB ternary device can achieve significantly enhanced power conversion efficiency of 14.09%.

Ternary strategy has been demonstrated to be an effective way to improve power conversion efficiency (PCE) of single-junction organic solar cells (OSCs). Herein, high-efficiency ternary OSCs are fabricated based on the PBDB-T:DO-2F binary system and acceptor IDTT-OB with asymmetric side chains as the third component. The introduction of nonfullerene acceptors (NFAs) IDTT-OB as a third component can efficiently increase the compatibility of the ternary system, reduce the crystallinity of DO-2F, optimize the blend film morphology, improve the charge transport and collection, suppress the bimolecular recombination, and reduce the nonradiative energy loss (ΔE _nonrad). Finally, the PBDB-T:DO-2F:IDTT-OB-based ternary device exhibits a high PCE of 14.09% with V _oc of 0.87 V, J _sc of 21.47 mA cm⁻², and fill factor of 75.70%, which is about 30% higher than the corresponding PBDB-T:DO-2F- and PBDB-T:IDTT-OB-based binary devices. Meanwhile, the ternary device also achieves a very low ΔE _nonrad of 0.22 eV. This work indicates that the ternary strategy can effectively optimize morphology of active layer, reduce nonradiative energy loss, and further improve photovoltaic performance of OSCs.