Asymmetric Acceptors with Fluorine and Chlorine Substitution for Organic Solar Cells toward 16.83% Efficiency

Small‐molecule acceptors (SMAs)‐based organic solar cells (OSCs) have exhibited great potential for achieving high power conversion efficiencies (PCEs). Meanwhile, developing asymmetric SMAs to improve photovoltaic performance by modulating energy level distribution and morphology has drawn lots of attention. In this work, based on the high‐performance SMA (Y6), three asymmetric SMAs are developed by substituting the fluorine atoms on the terminal group with chlorine atoms, namely SY1 (two F atoms and one Cl atom), SY2 (two F atoms and two Cl atoms), and SY3 (three Cl atoms). Y6 (four F atoms) and Y6‐4Cl (four Cl atoms) are synthesized as control molecules. As a result, SY1 exhibits the shallowest lowest unoccupied molecular orbital energy level and the best molecular packing among these five acceptors. Consequently, OSCs based on PM6:SY1 yield a champion PCE of 16.83% with an open‐circuit voltage (V_OC) of 0.871 V, and a fill factor (FF) of 0.760, which is the best result among the five devices. The highest FF for the PM6:SY1‐based device is mainly ascribed to the most balanced charge transport and optimal morphology. This contribution provides deeper understanding of applying asymmetric molecule design method to further promote PCEs of OSCs.     

Molecular Orientation Unified Nonfullerene Acceptor Enabling 14% Efficiency As‐Cast Organic Solar Cells

Molecular orientation and π–π stacking of nonfullerene acceptors (NFAs) determine its domain size and purity in bulk‐heterojunction blends with a polymer donor. Two novel NFAs featuring an indacenobis(dithieno[3,2‐b:2?,3?‐d]pyrrol) core with meta‐ or para‐alkoxyphenyl sidechains are designed and denoted as m‐INPOIC or p‐INPOIC , respectively. The impact of the alkoxyl group positioning on molecular orientation and photovoltaic performance of NFAs is revealed through a comparison study with the counterpart ( INPIC‐4F ) bearing para‐alkylphenyl sidechains. With inward constriction toward the conjugated backbone, m‐INPOIC presents predominant face‐on orientation to promote charge transport. The as‐cast organic solar cells (OSCs) by blending m‐INPOIC and PBDB‐T as active layers exhibit a power conversion efficiency (PCE) of 12.1%. By introducing PC₇₁BM as the solid processing‐aid, the ternary OSCs are further optimized to deliver an impressive PCE of 14.0%, which is among the highest PCEs for as‐cast single‐junction OSCs reported in literature to date. More attractively, PBDB‐T: m‐INPOIC :PC₇₁BM based OSCs exhibit over 11% PCEs even with an active layer thickness over 300 nm. And the devices can retain over 95% of PCE after storage for 20 days. The outstanding tolerance to film thickness and outstanding stability of the as‐cast devices make m‐INPOIC a promising candidate NFA for large‐scale solution‐processable OSCs.     

Over 15% Efficiency Polymer Solar Cells Enabled by Conformation Tuning of Newly Designed Asymmetric Small‐Molecule Acceptors

The prosperous period of polymer solar cells (PSCs) has witnessed great progress in molecule design methods to promote power conversion efficiency (PCE). Designing asymmetric structures has been proved effective in tuning energy level and morphology, which has drawn strong attention from the PSC community. Two hepta‐ring and octa‐ring asymmetric small molecular acceptors (SMAs) (IDTP‐4F and IDTTP‐4F) with S‐shape and C‐shape confirmations are developed to study the relationship between conformation shapes and PSC efficiencies. The similarity of absorption and energy levels between two SMAs makes the conformation a single variable. Additionally, three wide‐bandgap polymer donors (PM6, S1, and PM7) are chosen to prove the universality of the relationship between conformation and photovoltaic performance. Consequently, the champion PCE afforded by PM7: IDTP‐4F is as high as 15.2% while that of PM7: IDTTP‐4F is 13.8%. Moreover, the S‐shape IDTP‐4F performs obviously better than their IDTTP‐4F counterparts in PSCs regardless of the polymer donors, which confirms that S‐shape conformation performs better than the C‐shape one. This work provides an insight into how conformations of asymmetric SMAs affect PCEs, specific functions of utilizing different polymer donors to finely tune the active‐layer morphology and another possibility to reach an excellent PCE over 15%.     

Naphthodithiophene Diimide (NDTI)-Based Cathode Interlayer Material Enables 19% Efficiency Binary Organic Solar Cells

A fused naphthodithiophene diimide (NDTI) derivative is first used as cathode interlayer materials (CIMs) in organic solar cells, by introducing two dimethylamine-functionalized fluorenes on both sides, namely NDTI1 . Meanwhile, two non-fused naphthalene diimide (NDI) derivatives are synthesized as the control CIMs to validate the design strategy of fused NDI. All three CIMs show high thermal stability, robust adhesion, and strong electrode modification capability. Compared with two NDI-based materials, NDTI1 possesses excellent film-forming capacity and strong crystallinity, simultaneously. Besides, NDTI1 presents a strong self-doping effect and distinct intermolecular interaction with non-fullerene acceptors. As expected, the NDTI1 -based OSCs achieve a power conversion efficiency (PCE) of 18.02% using the PM6:Y6 active layer and a champion PCE of 19.01% employing the active layer PM6:L8-BO, which is attributed to improve charge transport and extraction, and suppressive charge recombination. More importantly, NDTI1 retains 91% of the optimal PCE when the film thickness increases from 7 to 20 nm. Furthermore, NDTI1 also exhibits satisfactory universality for different active layer materials and excellent device stability.     

Efficient Hole Transfer via Delocalized Excited State in Small Molecular Acceptor: A Comparative Study on Photodynamics of PM6:Y6 and PM6:ITIC Organic Photovoltaic Blends

Organic solar cells (OSCs) based on small molecular acceptors (SMAs) have made great development with a power conversion efficiency (PCE) over 16% due to the design of novel materials and advances in device preparation technology. This work fabricates two bulk-heterojunction photovoltaic devices containing the same wide-bandgap donor PM6, respectively, matched with popular Y6 and ITIC SMAs. The PM6:Y6-based device achieves a much higher PCE of 15.21% than the PM6:ITIC-based device of 9.02%. On the basis of comparisons of macroscopic performances in the quasistatic regime, transient absorption spectroscopy (TAS) is further performed to better understand the microscopic dynamics difference in charge separation processes between the two photovoltaic blends. According to the TAS results, the calculated hole transfer efficiency in PM6:Y6 is 71.4%, far greater than the efficiency of 13.1% in PM6:ITIC, demonstrating favorable charge separation at donor/acceptor interfaces via hole transfer channel in PM6:Y6. The favorable hole transfer in PM6:Y6 is accounted for by its better mutual miscibility between the donor and acceptor, and the formation of long-lived delocalized intramoiety excimer state in the acceptor. These results highlight the important role of proper molecular design strategy with strong intermolecular coupling and beneficial film morphology on facilitating charge generation in OSCs adopting SMAs.     

Versatile Self-Assembled Hole Transport Monolayer Enables Facile Processing Organic Solar Cells over 18% Efficiency with Good Generality

Simplifying solution-processing of bulk-heterojunction (BHJ) organic solar cells (OSCs) via efficient interfacial layers with good generality is in great demand for pushing their large-scale applications. In this study, such a novel and cost-effective self-assembled monolayer (SAM) is reported herein as efficient hole transport layer (HTL) for high efficiency OSCs. The SAM-structured 4-(5,9-dibromo-7H-dibenzo[c,g]carbazol-7-yl)butyl)phosphonic acid (DCB-BPA) enables not only enhanced photon harvesting in the active layer but also minimized nonradiative recombination losses to improve interface charge extraction/transport. As a consequence, high short-circuit current (≈28.07 mA cm⁻²) is achieved for PM6:BTP-eC9 based OSCs to deliver a champion power conversion efficiency of 18.16%, among the highest values for OSCs using small organic HTLs to date. Importantly, good generality of this SAMs is demonstrated for representative high-efficiency BHJ OSCs systems like PM6:Y6 and PM6:PC₆₁BM, outperforming conventional poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate)-based counterparts. Excitingly, the SAM is applicable for large-area HTL processing via immersion method, affording 16.59% efficiency for PM6:BTP-BO-4Cl based OSCs. This study highlights the great potential of engineered SAMs for facile large-scale fabrication of high performance OSCs.     

Importance of Terminal Group Pairing of Polymer Donor and Small-Molecule Acceptor in Optimizing Blend Morphology and Voltage Loss of High-Performance Solar Cells

As a variety of non-fullerene small molecule acceptors (SMAs) have been developed to improve power conversion efficiency (PCE) of organic solar cells (OSCs), the pairing of the SMAs with optimal polymer donors (P_Ds) is an important issue. Herein, a systematic investigation is conducted with the development of the SMA series, named C6OB-H, C6OB-Me, and C6OB-F, which contain distinctive terminal substituents –H, –CH₃, and –F, respectively. These SMAs are paired with two P_Ds, PBDT-H and PBDT-F. Interestingly, the P_D/SMA pairs with similar terminal groups yield enhanced molecular compatibility and energetic interactions, which suppress voltage loss while improving blend morphology to enhance simultaneously the open–circuit voltage, short–circuit current, and fill factor of the OSCs. In particular, the OSC based on the PBDT-F:C6OB-F blend sharing fluorine terminal groups achieves the highest PCE of 15.2%, which outperforms those of PBDT-H:C6OB-F (10.1%) and PBDB-F:C6OB-H OSCs (11.2%). Furthermore, the PBDT-F:C6OB-F OSC maintains high PCEs with active layer thicknesses between 85 and 310 nm. In contrast, the PCE of PBDT-H:C6OB-F-based OSC already drops by 80% from 10.1% to 2.1% when the active layer thickness increases from 100 to 200 nm. This study establishes an important P_D/SMA pairing rule in terms of terminal functional groups for achieving high-performance OSC.     

Efficient Ternary Organic Solar Cells Enabled by the Integration of Nonfullerene and Fullerene Acceptors with a Broad Composition Tolerance

The ternary structure that combines fullerene and nonfullerene acceptors in a photoactive layer is demonstrated as an effective approach for boosting the power conversion efficiencies (PCEs) of organic solar cells (OSCs). Here, highly efficient ternary OSCs comprising a wide‐bandgap polymer donor (PBT1‐C), a narrow‐bandgap nonfullerene acceptor (IT‐2F), and a typical fullerene derivative (PC₇₁BM) are reported. It is found that the addition of PC₇₁BM into the PBT1‐C:IT‐2F blend not only increases the device efficiency up to 12.2%, but also improves the ambient stability of the OSCs. Detailed investigations indicate that the improvement in photovoltaic performance benefits from synergistic effects of increased photon‐harvesting, enhanced charge separation and transport, suppressed trap‐assisted recombination, and optimized film morphology. Moreover, it is noticed that such a ternary system exhibits excellent tolerance to the PC₇₁BM component, for which PCEs over 11.2% can be maintained throughout the whole blend ratios, higher than that (11.0%) of PBT1‐C:IT‐2F binary reference device.     

Hydrogen Bond Induced Green Solvent Processed High Performance Ternary Organic Solar Cells with Good Tolerance on Film Thickness and Blend Ratios

For comprehensive development of organic solar cells (OSCs), some factors such as environmental stability, low cost, insensitive film thickness, component contents tolerance, and green preparation processes are equally crucial to achieve high power conversion efficiencies (PCEs). In this work, a small molecule 3‐(diethylamino)‐7‐imino‐7H‐benzo[4,5]imidazo[1,2‐a]chromeno[3,2‐c]pyridine‐6‐carbonitrile (DIBC), which is commercially available at low cost, is utilized to realize high‐performance ternary OSCs. Demonstrated via Fourier transform infrared and 2D‐¹HNMR, DIBC can form hydrogen bond interactions with [6,6]‐phenyl‐C₇₁‐butyric acid methyl ester (PC₇₁BM) in solid films. Further electrostatic potential (ESP) calculations indicate that the hydrogen bond interaction enhances the ESP of PC₇₁BM and accelerates charge transport between donor and acceptor. As a result, poly(4,8‐bis(5‐(2‐ethylhexyl)thiophen‐2‐yl)benzo[1,2‐b;4,5‐b0]dithiophene‐2,6‐diylalt‐(4‐(2‐ethylhexyl)‐3‐fluorothieno[3,4‐b]thiophene‐)‐2‐carboxylate‐2‐6‐diyl (PTB7‐Th):DIBC:PC₇₁BM‐based ternary OSC achieves a maximum efficiency of 12.17%, which is the best result of green solvent processed fullerene OSCs at present. It is noteworthy that the ternary OSCs also show great tolerance to film thickness and blend ratios. These unique properties are attributed to the hydrogen‐bond‐linked DIBC and PC₇₁BM, which modulates molecule distribution and improves film morphology with an interpenetrating network structure. Furthermore, the DIBC containing device also exhibits good thermal and light radiation stability. These results illustrate that intermolecular hydrogen bond interaction has great potential for realizing high‐performance OSCs.     

High-Efficiency (16.93%) Pseudo-Planar Heterojunction Organic Solar Cells Enabled by Binary Additives Strategy

Acquiring precision adjustable morphology of the blend films to improve the efficiency of charge separation and collection is a constant goal of organic solar cells (OSCs). Here, the above problem is improved by synergistically combining the sequential deposition (SD) method and the additive general strategy. By adding one additive 1,10-decanediol (DDO) into PM6 and another 1-chloronaphthalene (CN) into Y6, the molecule orientation of PM6 and the crystallite texture of the Y6 all become order. During the SD processing, a vertical phase separation OSCs device is formed where the donor enrichment at the anode and acceptor enrichment at the cathode. In comparison, the SD OSCs device with only CN additive still displays the bulk-heterojunction morphology similar to PM6:Y6 blend film. The morphology with vertical phase distribution can not only inhibit charge recombination but also facilitate charge collection, finally enhancing the fill factor (FF) and photocurrent in binary additives SD-type OSCs. As a result, the binary additives SD-type OSCs with blend film PM6 + DDO/Y6 + CN exhibit a high FF of 77.45%, enabling a power conversion efficiency as high as 16.93%. This work reveals a simple but effective approach for boosting high-efficiency OSCs with ideal morphologies and demonstrates that the additive is a promising processing alternative.     

High-Performance Green Thick-Film Ternary Organic Solar Cells Enabled by Crystallinity Regulation

The power conversion efficiency (PCE) of organic solar cells (OSCs) has reached high values of over 19%. However, most of the high-efficiency OSCs are fabricated by spin-coating with toxic solvents and the optimal photoactive layer thickness is limited to 100 nm, limiting practical development of OSCs. It is a great challenge to obtain ideal morphology for high-efficiency thick-film OSCs when using non-halogenated solvents due to the unfavorable film formation kinetics. Herein, high-efficiency ternary thick-film (300 nm) OSCs with PCE of 15.4% based on PM6:BTR-Cl:CH1007 are fabricated by hot slot-die coating using non-halogenated solvent (o-xylene) in the air. Compared to PM6:BTR-Cl:Y6 blends, the stronger pre-aggregation of CH1007 in solution induces the earlier aggregation of CH1007 molecules and longer aggregation time, and thus results in high and balanced crystallinity of donors and acceptor in CH1007-based ternary film, which led to high-carrier mobility and suppressed charge recombination. The ternary strategy is further used to fabricate high-efficiency, thick-film, large-area, and flexible devices processed from non-halogenated solvents, paving the way for industrial development of OSCs.     

Novel brominated compounds using in binary additives based organic solar cells to achieve high efficiency over 10.3%

Solvent additives have been considered as a simple and efficient method to increase the performance of bulk-heterojunction (BHJ) organic solar cells, in which, the morphology of the active layer could obtain further improvements by using the binary solvent additives. In this paper, a series of brominated compounds, 1-Bromo-4-butylbenzene (Brbb), 1-Bromo-4-n-hexylbenzene (Brbh) and 1-Bromo-4-n-octylbenzene (Brbo), have been respectively incorporated with 1, 8-diiodooctane (DIO) and regarded as binary solvent additives to fabricate highly efficient bulk heterojunction (BHJ) organic solar cells (OSCs). Compared with the BHJ film based on single additive, the binary additives contained BHJ film shows increased optical absorption, efficient charge transport and better active layer morphology, leading to an enhancement of short-circuit current (J_SC) together with a higher achieved fill factor (FF). The conventional BHJ device using PTB7: PC₇₁BM or PTB7-th: PC₇₁BM with the binary solvent additives exhibit enhanced PCE of 8.13% and 10.31%, respectively, which is much higher than that of single additive based devices (7.04% for PTB7 and 8.73% for PTB7-th). The optimized performance of BHJ devices indicates that these brominated compounds are promising additives to improve device efficiency.     

Plasmonic Electrically Functionalized TiO2 for High‐Performance Organic Solar Cells

Optical effects of the plasmonic structures and the materials effects of the metal nanomaterials have recently been individually studied for enhancing performance of organic solar cells (OSCs). Here, the effects of plasmonically induced carrier generation and enhanced carrier extraction of the carrier transport layer (i.e., plasmonic‐electrical effects) in OSCs are investigated. Enhanced charge extraction in TiO₂ as a highly efficient electron transport layer by the incorporation of metal nanoparticles (NPs) is proposed and demonstrated. Efficient device performance is demonstrated by using Au NPs incorporated TiO₂ at a plasmonic wavelength (560–600 nm), which is far longer than the originally necessary UV light. By optimizing the concentration ratio of the Au NPs in the NP‐TiO₂ composite, the performances of OSCs with various polymer active layers are enhanced and efficiency of 8.74% is reached. An integrated optical and electrical model, which takes into account plasmonic‐induced hot carrier tunneling probability and extraction barrier between TiO₂ and the active layer, is introduced. The enhanced charge extraction under plasmonic illumination is attributed to the strong charge injection of plasmonically excited electrons from NPs into TiO₂. The mechanism favors trap filling in TiO₂, which can lower the effective energy barrier and facilitate carrier transport in OSCs.     

A two-dimension-conjugated small molecule for efficient ternary organic solar cells

Ternary organic solar cells (OSCs) are burgeoning as one of the effective strategies to achieve high power conversion efficiencies (PCEs) by incorporating a third component with a complementary absorption into the binary blends. In this study, we presented a new two-dimension-conjugated small molecule denoted by DR3TBDTTVT, which alone gave rise to a best PCE of 5.71% with acceptor PC₇₁BM as active layer. Given the complementary absorption with PTB7-Th, DR3TBDTTVT was doped into (PTB7-Th:PC₇₁BM)-based binary blends, and ternary OSCs were developed. The ternary OSCs with 10 wt% of DR3TBDTTVT displayed improved hole-mobility, reduced device resistance and better phase separation of active layer, thus leading to an impressive PCE of 7.77% with open-circuit voltage of 0.77 V, short-circuit density of 14.52 mA cm⁻² and fill factor of 70.3%. Ternary OSCs well make up for the light-harvesting insufficiency of binary OSCs, and this research provides a new material for the improvement of PCEs for single-junction OSCs.     

Monomolecular and Bimolecular Recombination of Electron–Hole Pairs at the Interface of a Bilayer Organic Solar Cell

While it has been argued that field‐dependent geminate pair recombination (GR) is important, this process is often disregarded when analyzing the recombination kinetics in bulk heterojunction organic solar cells (OSCs). To differentiate between the contributions of GR and nongeminate recombination (NGR) the authors study bilayer OSCs using either a PCDTBT‐type polymer layer with a thickness from 14 to 66 nm or a 60 nm thick p‐DTS(FBTTh₂)₂ layer as donor material and C₆₀ as acceptor. The authors measure JV‐characteristics as a function of intensity and charge‐extraction‐by‐linearly‐increasing‐voltage‐type hole mobilities. The experiments have been complemented by Monte Carlo simulations. The authors find that fill factor (FF) decreases with increasing donor layer thickness (L_p) even at the lowest light intensities where geminate recombination dominates. The authors interpret this in terms of thickness dependent back diffusion of holes toward their siblings at the donor–acceptor interface that are already beyond the Langevin capture sphere rather than to charge accumulation at the donor–acceptor interface. This effect is absent in the p‐DTS(FBTTh₂)₂ diode in which the hole mobility is by two orders of magnitude higher. At higher light intensities, NGR occurs as evidenced by the evolution of s‐shape of the JV‐curves and the concomitant additional decrease of the FF with increasing layer thickness.     

Quantifying charge transportation for stable organic solar cells with a novel aluminum acetylacetone electron collection layer

Elucidating charge transportation mechanism for low-temperature solution-processed charge collection layer is crucial for efficient and stable organic solar cells (OSCs). Herein, we present a facile method to fabricate Al(acac)₃ film and integrate it as electron collection layer (ECL) in OSCs. The PM6:Y6-based OSCs with Al(acac)₃ ECL achieve a higher efficiency of 16.12% as compared to the control devices with a 10.90% efficiency. Importantly, the Al(acac)₃-based devices present superior operational stability, which retains 60% of the initial PCE after 100 h continuous illumination in air. Investigations on optics and carrier recombination dynamics reveal that the improved performance benefits from high up to 98% transparency of Al(acac)₃ ECL, optimized interfacial contact and enhanced exciton dissociation ratio from 85.10% to 97.51%. Further studies on quantified interface resistances during the internal charge transfer indirectly reflect the enhancement of stability. These results highlight the promising prospect of Al(acac)₃ ECL in processing compatible, operationally stable high efficiency OSCs.     

Indoline‐Based Molecular Engineering for Optimizing the Performance of Photoactive Thin Films

New indoline dyes ( RK‐1 – 4 ) were designed with a planar geometry and high molar extinction coefficient, which provided surprising power conversion efficiency (PCE) with a thin titanium dioxide film in dye‐sensitized solar cells (DSCs). They had a difference in only alkyl chain length. Despite the same molecular structure, the performance of the respective DSCs varied significantly. Investigating the dye adsorption processes and charge transfer kinetics, the alkyl chain length was determined to affect the dye surface coverage as well as the recombination between the injected photoelectrons and the oxidized redox mediators. When applied to the DSCs as a light harvester, RK‐3 with the dodecyl group exhibited the best photocurrent density, consequently achieving the best PCE of 9.1% with a 1.8 μm active and 2.5 μm scattering layer because of the most favorable charge injection. However, when increasing the active layer thickness, overall device performance deteriorated and the charge collection and regeneration played major roles for determining the PCE. Therefore, RK‐2 featuring the highest surface coverage and moderate alkyl chain length obtained the highest PCEs of 8.8% and 7.9% with 3.5 and 5.1 μm active layers, respectively. These results present a promising perspective of organic dye design for thin film DSCs.     

Investigating the reason for high FF from ternary organic solar cells

Organic solar cells (OSCs) have attracted huge attention because of their unique merits[1-3].In last few years,thanks to the design of new materials and device engineering,the power conversion efficiencies (PCEs) of OSCs have surpassed 18％[4-8].The PM6:Y6 cells are efficient binary cells,offering high PCEs over 16％[9-11].The high performance originates from the efficient free charge generation and the ground state dipole field at the donor-acceptor interface that pro-motes the exciton dissociation[12].To further boost the per-formance of PM6:Y6 cells,ternary architectures were adop-ted.Significant improvements in short-circuit current density(Jsc) and open-circuit voltage (Voc) were realized.However,most of the ternary cells still suffer from low fill factor (FF) (gen-erally ＜78％) (Table S1).The FF is generally determined by the competition between recombination and extraction of charge carriers[13-15].The interfacial electronic structures have nonnegligible impacts on charge transport in OSCs,also influ-encing the FF[16,17].Previously,Bao et al.demonstrated that the energy of positive integer charge transfer (ICT) states(EICT+) of PM6 is equal to the energy of negative ICT states(EICT-) of Y6,leading to no potential step at the PM6:Y6 inter-face and an ideal binary host system[18].To avoid the forma-tion of potential step in the ternary system,the EICT-of the second acceptor should be lower than (or equal to) EICT+ of the donor,thus suppressing the ICT trap-assisted recombina-tion[1].In this work,we carefully incorporate a second accept-or EH-IDTBR into the host PM6:Y6 blend (Fig.1(a)).From the ultraviolet photoelectron spectroscopy (UPS)-derived energy levels (Fig.1(b)),the negative ICT states of EH-IDTBR (EICT-=4.25 eV) is smaller than the positive ICT states of PM6 (EICr+ =4.5 eV),suggesting no ground state charge transfer at the PM6:EH-IDTBR interface,thus avoiding interfacial ICT trap-assisted recombination.     

Boosting Performance of Non‐Fullerene Organic Solar Cells by 2D g‐C3N4 Doped PEDOT:PSS

The power‐conversion efficiency (PCE) of single‐junction organic solar cells (OSCs) has exceeded 16% thanks to the development of non‐fullerene acceptor materials and morphological optimization of active layer. In addition, interfacial engineering always plays a crucial role in further improving the performance of OSCs based on a well‐established active‐layer system. Doping of graphitic carbon nitride (g‐C₃N₄) into poly(3,4‐ethylene‐dioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) as a hole transport layer (HTL) for PM6:Y6‐based OSCs is reported, boosting the PCE to almost 16.4%. After being added into the PEDOT:PSS, the g‐C₃N₄ as a Bronsted base can be protonated, weakening the shield effect of insulating PSS on conductive PEDOT, which enables exposures of more PEDOT chains on the surface of PEDOT:PSS core‐shell structure, and thus increasing the conductivity. Therefore, at the interface between g‐C₃N₄ doped HTL and PM6:Y6 layer, the charge transport is improved and the charge recombination is suppressed, leading to the increases of fill factor and short‐circuit current density of devices. This work demonstrates that doping g‐C₃N₄ into PEDOT:PSS is an efficient strategy to increase the conductivity of HTL, resulting in higher OSC performance.     

Secondary Bonds Modifying Conjugate‐Blocked Linkages of Biomass‐Derived Lignin to Form Electron Transfer 3D Networks for Efficiency Exceeding 16% Nonfullerene Organic Solar Cells

Fabricating high‐efficient electron transporting interfacial layers (ETLs) with isotropic features is highly desired for all‐directional electron transfer/collection from an anisotropic active layer, achieving excellent power conversion efficiency (PCEs) on nonfullerene acceptor (NFA) organic solar cells (OSCs). The complicated synthesis and cost‐consumption in exploring versatile materials arouse great interest in the development of binary‐doping interlayers without phase separation and flexible manipulation. Herein, for the first time, a novel cathode interfacial layer based on biomass‐derived demethylated kraft lignin (D_MeKL) is proposed. Features of multiple phenolic‐hydroxyl (PhOH) and uniform‐distributed render D_MeKL to exhibit an excellent bonding capacity with amino terminal substituted perylene diiminde (PDIN), and successfully form a high‐efficient isotropic electron transfer 3D network. Synchronously, secondary bonds completely modify conjugate‐blocked linkages of D_MeKL, significantly enhance the electron transporting performance on cross‐section and vertical‐sections, and repair the contact of PDIN with active layer. The D_MeKL/PDIN‐based 3D‐network exhibits well‐matched work function (WF) (–4.34 eV) with cathode (–4.30 eV) and energy level of electron acceptor (–4.11 eV). D_MeKL/PDIN‐based NFAs‐OSC shows excellent short‐circuit current density (26.61 mA cm^–2) and PCE (16.02%) beyond the classic PDIN‐based NFA‐OSC (25.64 mA cm^–2, 15.41%), which is the highest PCEs among biomaterials interlayers. The results supply a novel method to achieve high‐efficient cathode interlayer for NFAs‐OSCs.