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The effects of cathode modification by a conjugated polymer interlayer PFPA1 on the performance of reversed organic solar cells (substrate/cathode/active layer/transparent anode) based on different active material systems and different substrate electrodes are systematically investigated. A reduction of the work function irrespective of the substrate cathode used is observed upon the deposition of the PFPA1 interlayer, which is further related to an improved built-in electric field and open-circuit voltage. The amphiphilic character of the PFPA1 interlayer alters the surface energy of the substrate cathode, leading to the formation of a better active layer morphology aiding efficient exciton dissociation and photocurrent extraction in the modified solar cells. Hence, internal quantum efficiency is found to be significantly higher than that of their unmodified counterparts, while optically, the modified and unmodified solar cells are identical. Moreover, the deep highest occupied molecular orbital (HOMO) of the PFPA1 interlayer improves the selectivity for all investigated substrate cathodes, thus enhancing the fill factor. [ABSTRACT FROM AUTHOR]

A major issue in organic solar cells is the poor mobility and recombination of the photogenerated charge carriers. The active layer has to be kept thin to facilitate charge transport and minimize recombination losses. However, optical losses due to inefficient light absorption in the thin active layers can be considerable in organic solar cells. Therefore, light trapping schemes are critically important for efficient organic solar cells. Traditional light trapping schemes for thick solar cells need to be modified for organic thin film solar cells in which coherent optics and wave effects play a significant role. In this review, we discuss the light trapping schemes for organic thin film solar cells, which includes geometric engineering of the structure of the solar cell at the micro and nanoscale, plasmonic structures, and more. [ABSTRACT FROM AUTHOR]

Fluorination strategy is demonstrated to be a successful approach for optimizing the electron distribution and morphology of organic photovoltaic materials. The previous works focus on introducing only a few C(sp2)─F bonds into conjugated backbone or C(sp3)─F bonds into sidechains. Herein, a new strategy by introducing C(sp3)─F polyfluoride unit into the backbone is proposed, wherein the fluorine atoms are not involved into the conjugation but can promote the intermolecular interaction between backbones. Two wide‐bandgap fluoropolymers are prepared and employed as the third component for ternary organic solar cells. As expected, even if there are six fluorine atoms in a single repeat unit, the relevant fluoropolymers possess complementary absorption and aligned energy levels. More importantly, the polyfluoride backbone affords adequate non‐covalent interactions, consequently enhancing the polymer aggregation and packing order, which is verified by a fibril‐like morphology in the blend film with the host polymer PM6 and only 10 wt.% fluoropolymer. In addition, the decreased surface energy caused by polyfluoride unit is beneficial for the improvement of domain purity and the formation of nanoscale phase separation between donor and acceptor materials. As a result, the fluoropolymer‐assisted ternary device displays a higher efficiency of 18.74% compared with the binary device (17.39%). [ABSTRACT FROM AUTHOR]

Trap states in organic solar cells (OSCs) can capture free charges, leading to a reduction in current density and significant energy loss. Since charge collection is primarily dependent on the interface layer, minimizing trap states at interfaces can effectively suppress energy losses, a topic that has been rarely explored. Herein, an interface strategy is proposed by combining Me‐4PACz and PEDOT:PSS to mitigate the trap‐assisted nonradiative recombination at the hole transport layer (HTL). OSCs based on the Me‐4PACz/PEDOT:PSS exhibit reduced trap densities and low energy losses compared to devices fabricated with a single‐layer HTL. This reduction can be attributed to a lower nonradiative recombination rate during hole transport at the interface. Changes in the work function of the two interlayers due to contact result in the existence of a built‐in potential inside the composite interlayer, promoting charge collection and reducing energy loss from charge recombination. Furthermore, the composite HTL interface induces vertical phase separation of active layer, leading to significant improvements of the fill factor for OSCs. As a result, high power conversion efficiencies (PCEs) of 18.70% and 19.02% are achieved for binary all‐polymer solar cells and polymer donor/small molecule acceptor solar cells, respectively. [ABSTRACT FROM AUTHOR]

The development of high‐efficiency organic solar cells (OSCs) processed from non‐halogenated solvents is crucially important for their scale‐up industry production. However, owing to the difficulty of regulating molecular aggregation, there is a huge efficiency gap between non‐halogenated and halogenated solvent processed OSCs. Herein, we fabricate o‐xylene processed OSCs with approaching 20 % efficiency by incorporating a trimeric guest acceptor named Tri‐V into the PM6:L8‐BO‐X host blend. The incorporation of Tri‐V effectively restricts the excessive aggregation of L8‐BO‐X, regulates the molecular packing and optimizes the phase‐separation morphology, which leads to mitigated trap density states, reduced energy loss and suppressed charge recombination. Consequently, the PM6:L8‐BO‐X:Tri‐V‐based device achieves an efficiency of 19.82 %, representing the highest efficiency for non‐halogenated solvent‐processed OSCs reported to date. Noticeably, with the addition of Tri‐V, the ternary device shows an improved photostability than binary PM6:L8‐BO‐X‐based device, and maintains 80 % of the initial efficiency after continuous illumination for 1380 h. This work provides a feasible approach for fabricating high‐efficiency, stable, eco‐friendly OSCs, and sheds new light on the large‐scale industrial production of OSCs. [ABSTRACT FROM AUTHOR]

The development of high‐efficiency organic solar cells (OSCs) processed from non‐halogenated solvents is crucially important for their scale‐up industry production. However, owing to the difficulty of regulating molecular aggregation, there is a huge efficiency gap between non‐halogenated and halogenated solvent processed OSCs. Herein, we fabricate o‐xylene processed OSCs with approaching 20 % efficiency by incorporating a trimeric guest acceptor named Tri‐V into the PM6:L8‐BO‐X host blend. The incorporation of Tri‐V effectively restricts the excessive aggregation of L8‐BO‐X, regulates the molecular packing and optimizes the phase‐separation morphology, which leads to mitigated trap density states, reduced energy loss and suppressed charge recombination. Consequently, the PM6:L8‐BO‐X:Tri‐V‐based device achieves an efficiency of 19.82 %, representing the highest efficiency for non‐halogenated solvent‐processed OSCs reported to date. Noticeably, with the addition of Tri‐V, the ternary device shows an improved photostability than binary PM6:L8‐BO‐X‐based device, and maintains 80 % of the initial efficiency after continuous illumination for 1380 h. This work provides a feasible approach for fabricating high‐efficiency, stable, eco‐friendly OSCs, and sheds new light on the large‐scale industrial production of OSCs. [ABSTRACT FROM AUTHOR]

In the development of high‐performance organic solar cells (OSCs), the self‐organization of organic semiconductors plays a crucial role. This study focuses on the precisely manipulation of molecular assemble via tuning alkyl side‐chain topology in a series of low‐cost nonfused‐ring electron acceptors (NFREAs). Among the three NFREAs investigated, DPA‐4, which possesses an asymmetric alkyl side‐chain length, exhibits a tight packing in the crystal and high crystallinity in the film, contributing to improved electron mobility and favorable film morphology for DPA‐4. As a result, the OSC device based on DPA‐4 achieves an excellent power conversion efficiency of 16.67 %, ranking among the highest efficiencies for NFREA‐based OSCs. [ABSTRACT FROM AUTHOR]

In the development of high‐performance organic solar cells (OSCs), the self‐organization of organic semiconductors plays a crucial role. This study focuses on the precisely manipulation of molecular assemble via tuning alkyl side‐chain topology in a series of low‐cost nonfused‐ring electron acceptors (NFREAs). Among the three NFREAs investigated, DPA‐4, which possesses an asymmetric alkyl side‐chain length, exhibits a tight packing in the crystal and high crystallinity in the film, contributing to improved electron mobility and favorable film morphology for DPA‐4. As a result, the OSC device based on DPA‐4 achieves an excellent power conversion efficiency of 16.67 %, ranking among the highest efficiencies for NFREA‐based OSCs. [ABSTRACT FROM AUTHOR]

A pyrene‐fused dimerized electron acceptor has been successfully synthesized and subsequently incorporated as the third component in ternary organic solar cells (OSCs). Diverging from the traditional dimerized acceptors with a linear configuration, this novel electron acceptor displays a distinctive "butterfly‐like" structure, comprising two Y‐acceptors as wings fused with a pyrene‐based backbone. The extended π‐conjugated backbone and the electron‐donating nature of pyrene enable the new acceptor to show low solubility, elevated glass transition temperature (Tg), and low‐lying frontier energy levels. Consequently, the new dimerized acceptor seamlessly integrates as the third component into ternary OSCs, enhancing electron transporting properties, reducing non‐radiative voltage loss, and elevating open‐circuit voltage. These merits have enabled the ternary OSCs to show an exceptional efficiency of 19.07%, a marked improvement compared to the 17.6% attained in binary OSCs. More importantly, the high Tg exhibited by the pyrene‐fused electron acceptor helps to stabilize the morphology of the photoactive layer thermal‐treated at 70 °C, retaining 88.7% efficiency over 600 hours. For comparison, binary OSCs experience a decline to 73.7% efficiency after the same duration. These results indicate that the "butterfly‐like" design and the incorporation of a pyrene unit is a promising strategy in the development of dimerized electron acceptors for OSCs. [ABSTRACT FROM AUTHOR]

A pyrene‐fused dimerized electron acceptor has been successfully synthesized and subsequently incorporated as the third component in ternary organic solar cells (OSCs). Diverging from the traditional dimerized acceptors with a linear configuration, this novel electron acceptor displays a distinctive "butterfly‐like" structure, comprising two Y‐acceptors as wings fused with a pyrene‐based backbone. The extended π‐conjugated backbone and the electron‐donating nature of pyrene enable the new acceptor to show low solubility, elevated glass transition temperature (Tg), and low‐lying frontier energy levels. Consequently, the new dimerized acceptor seamlessly integrates as the third component into ternary OSCs, enhancing electron transporting properties, reducing non‐radiative voltage loss, and elevating open‐circuit voltage. These merits have enabled the ternary OSCs to show an exceptional efficiency of 19.07%, a marked improvement compared to the 17.6% attained in binary OSCs. More importantly, the high Tg exhibited by the pyrene‐fused electron acceptor helps to stabilize the morphology of the photoactive layer thermal‐treated at 70 °C, retaining 88.7% efficiency over 600 hours. For comparison, binary OSCs experience a decline to 73.7% efficiency after the same duration. These results indicate that the "butterfly‐like" design and the incorporation of a pyrene unit is a promising strategy in the development of dimerized electron acceptors for OSCs. [ABSTRACT FROM AUTHOR]

Nowadays, it is still a great challenge to obtain high‐performance green‐solvent‐processed organic solar cells (OSCs). In this study, a ternary blend strategy (one donor and two acceptors, 1D/2A) is developed to solve the difficulty of film morphology modulation during the fabrication of high‐performance green‐solvent‐processed OSCs. A typical high‐performance halogenated‐solvent processable binary system D18:BTP‐eC9‐4F is selected as the host, its green‐solvents‐processed devices show an inferior power conversion efficiency (PCE) of ≈16%. SM16 with two 3D shape persistent end groups is selected as the third component due to its high fluorescence quantum yield, reduced intermolecular interaction, good solubility, and moderate crystallinity. As a result, the ternary devices display bicontinuous interpenetrating networks, reduced energy loss, and suppressed charge carrier recombination losses. Hence, an excellent PCE of 18.20% is achieved for the D18:BTP‐eC9‐4F:SM16 ternary devices, which is much higher than D18:BTP‐eC9‐4F‐based binary ones and also one of the highest PCEs for the green‐solvents‐processed OSCs. Besides, this strategy also demonstrates a good universality for other binary systems and becomes an effective pathway for the development of green‐solvent processable high‐performance OSCs. [ABSTRACT FROM AUTHOR]

Comprehensive Summary: By simplifying the π‐bridge unit, a nonfused ring electron acceptor (NFREA) BM‐2F was designed and synthesized with several high‐yield steps. The specific molecular structure features of BM‐2F are planar molecular backbone and out‐of‐plane side chain, which is favorable for charge transport and can suppress the over‐aggregation. BM‐2F based neat and blend films display obvious face‐on molecular orientation. Specially, D18:BM‐2F based blend film can form good bicontinuous interpenetrating network. More excitingly, a power conversion efficiency of 16.15% was achieved with D18:BM‐2F based photovoltaic devices, which is the highest one based on NFREAs. Our researches manifest that NFREA is a promising direction for low‐cost and high‐performance organic solar cells. [ABSTRACT FROM AUTHOR]

Sequential deposition of the active layer in organic solar cells (OSCs) is favorable to circumvent the existing drawbacks associated with controlling the microstructure in bulk‐heterojunction (BHJ) device fabrication. However, how the processing solvents impact on the morphology during sequential deposition processes is still poorly understood. Herein, high‐efficiency OSCs are fabricated by a sequential blade coating (SBC) through optimization of the morphology evolution process induced by processing solvents. It is demonstrated that the device performance is highly dependent on the processing solvent of the upper layer. In situ morphology characterizations reveal that an obvious liquid–solid phase separation can be identified during the chlorobenzene processing of the D18 layer, corresponding to larger phase separation. During chloroform (CF) processing of the D18 layer, a proper aggregation rate of Y6 and favorable intermixing of lower and upper layers results in the enhanced crystallinity of the acceptor. This facilitates efficient exciton dissociation and charge transport with an inhibited charge recombination in the D18/CF‐based devices, contributing to a superior performance of 17.23%. These results highlight the importance of the processing solvent for the upper layer in the SBC strategy and suggest the great potential of achieving optimized morphology and high‐efficiency OSCs using the SBC strategy. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The large energy loss (Eloss) is one of the main obstacles to further improve the photovoltaic performance of organic solar cells (OSCs), which is closely related to the charge transfer (CT) state. Herein, ternary donor alloy strategy is used to precisely tune the energy of CT state (ECT) and thus the Eloss for boosting the efficiency of OSCs. The elevated ECT in the ternary OSCs reduce the energy loss for charge generation (ΔECT), and promote the hybridization between localized excitation state and CT state to reduce the nonradiative energy loss (ΔEnonrad). Together with the optimal morphology, the ternary OSCs afford an impressive power conversion efficiency of 19.22% with a significantly improved open‐circuit voltage (Voc) of 0.910 V without sacrificing short‐cicuit density (Jsc) and fill factor (FF) in comparison to the binary ones. This contribution reveals that precisely tuning the ECT via donor alloy strategy is an efficient way to minimize Eloss and improve the photovoltaic performance of OSCs. [ABSTRACT FROM AUTHOR]

Double‐cable conjugated polymers with near‐infrared (NIR) electron acceptors are synthesized for use in single‐component organic solar cells (SCOSCs). Through the development of a judicious synthetic pathway, the highly sensitive nature of the 2‐(3‐oxo‐2,3‐dihydroinden‐1‐ylidene)malononitrile (IC)‐based electron acceptors in basic and protonic solvents is overcome. In addition, an asymmetric design motif is adopted to optimize the packing of donor and acceptor segments, enhancing charge separation efficiency. As such, the new double‐cable polymers are successfully applied in SCOSCs, providing an efficiency of over 10 % with a broad photo response from 300 to 850 nm and exhibiting excellent thermal/light stability. These results demonstrate the powerful design of NIR‐acceptor‐based double‐cable polymers and will enable SCOSCs to enter a new stage. [ABSTRACT FROM AUTHOR]

Double‐cable conjugated polymers with near‐infrared (NIR) electron acceptors are synthesized for use in single‐component organic solar cells (SCOSCs). Through the development of a judicious synthetic pathway, the highly sensitive nature of the 2‐(3‐oxo‐2,3‐dihydroinden‐1‐ylidene)malononitrile (IC)‐based electron acceptors in basic and protonic solvents is overcome. In addition, an asymmetric design motif is adopted to optimize the packing of donor and acceptor segments, enhancing charge separation efficiency. As such, the new double‐cable polymers are successfully applied in SCOSCs, providing an efficiency of over 10 % with a broad photo response from 300 to 850 nm and exhibiting excellent thermal/light stability. These results demonstrate the powerful design of NIR‐acceptor‐based double‐cable polymers and will enable SCOSCs to enter a new stage. [ABSTRACT FROM AUTHOR]

Herein, we demonstrate a method to build highly efficient light trapping structures for printed organic solar cells and modules, compatible with roll to roll manufacturing. Echelle grating structures in combination with semitransparent electrodes allow for efficient light trapping via means of total internal reflection. With this method, we demonstrate an increased cell photocurrent response up to 24%, compared to a standard cell configuration with a planar reflector. The demonstrated light trapping approach is expected to be even more useful for photovoltaic modules, where light hitting 'dead areas' in between the sub-cells comprising the module will now be utilized. [ABSTRACT FROM AUTHOR]

Two new fused‐ring electron acceptor (FREA) isomers with nonlinear and linear molecular conformation, m‐BAIDIC and p‐BAIDIC, are designed and synthesized. Despite the similar light absorption range and energy levels, the two isomers exhibit distinct electron reorganization energies and molecular packing motifs, which are directly related to the molecular conformation. Compared with the nonlinear acceptor, the linear p‐BAIDIC shows more ordered molecular packing and higher crystallinity. Furthermore, p‐BAIDIC‐based devices exhibit reduced nonradiative energy loss and improved charge transport mobilities. It is beneficial to enhance the open‐circuit voltage (VOC) and short‐current current density (JSC) of the devices. Therefore, the linear FREA, p‐BAIDIC yields a relatively higher efficiency of 7.71% in the binary device with PM6, in comparison with the nonlinear m‐BAIDIC. When p‐BAIDIC is incorporated into the binary PM6/BO‐4Cl system to form a ternary system, synergistic enhancements in VOC, JSC, fill factor (FF), and ultimately a high efficiency of 17.6% are achieved. [ABSTRACT FROM AUTHOR]

Exaggerated charge losses from excited to charge transfer (CT) and ground states in bulk heterojunction (BHJ) structures results in small voltages (< 1 V) for organic solar cells (OSCs). Characterizing morphology‐voltage loss correlations is difficult due to the complexity of BHJ structures but promises the realization of 20% efficiency for OSCs. By utilizing two similar non‐fullerene acceptors (NFA) in a ternary blend, a pseudo‐binary system is constructed to control the acceptor composition and donor‐acceptor (D‐A) miscibility. Within the framework of miscibility‐morphology controlled device photovoltaics, it is found that higher D‐A miscibility results in enhanced domain purity, which is associated with inefficient excitons dissociation and improves the excited and CT state emission, thereby resulting in enhanced electroluminescence efficiency to reduce the non‐radiative (NR) loss contribution to device voltage. The simple but effective composition mediated morphology control identifies domain purity as one key feature to lower the NR recombination in high quantum yield polymer/NFA blends. [ABSTRACT FROM AUTHOR]

The semitransparent and colorful properties of organic solar cells (OSCs) attract intensive academic interests due to their potential application in building integrated photovoltaics, wearable electronics, and so forth. The most straightforward and effective method to tune these optical properties is varying the componential ratio in the blend film. However, the increase in device transmittance inevitably sacrifices the photovoltaic performance because of severe carrier recombination that originates from discontinuous charge‐transport networks in the blend film. Herein, a strategy is proposed via the molecular‐doping strategy to overcome these shortcomings. It is discovered that p‐doping is able to release the trapped holes in segregated polymer domains leading to short‐circuit current enhancement, while n‐doping is more effective to fill the bandgap states producing a higher fill factor. More importantly, either type of doping improves the photovoltaic performance in the semitransparent photovoltaic devices. These discoveries provide a new pathway to breaking the compromise between the photovoltaic performance and optical transmittance in semitransparent OSCs, and hold promise for their future commercialization. [ABSTRACT FROM AUTHOR]

Increasing the photoluminescence quantum yield (PLQY) of narrow bandgap acceptors is of critical importance to suppress the nonradiative voltage loss (ΔVnr) in organic solar cells (OSCs). Herein, two acceptors, SM16 and SM16‐R, with an identical backbone but different terminal groups (norbornenyl modified 1,1‐dicyanomethylene‐3‐indanone and dimethyl substituted 1,1‐dicyanomethylene‐3‐indanone) are designed and synthesized. Compared with SM16‐R, SM16 displays better solubility, higher PLQY, and more favorable nanomorphology when blended with polymer donor PBDB‐T. PBDB‐T:SM16‐based OSCs yield a ΔVnr as low as 0.145 V. Using SM16 as the third component, a high power conversion efficiency of 17.1% is achieved in the ternary OSCs based on PBDB‐T:Y14:SM16, considerably higher than that of the binary devices based on PBDB‐T:Y14 or PBDB‐T:SM16. These results highlight that enhancing the PLQY of low bandgap acceptor via terminal group engineering strategy is highly effective to reduce ΔVnr of OSCs. [ABSTRACT FROM AUTHOR]

The rapid advance of fused‐ring electron acceptors (FREAs) has greatly promoted the leap‐forward development of organic solar cells (OSCs). However, the synthetic complexity of FREAs may be detrimental for future commercial applications. Recently, nonfused‐ring electron acceptors (NREAs) have been developed to be a promising candidate to maintain a rational balance between cost and performance, of which the cores are composed of simple fused rings (NREAs‐I) or nonfused rings (NREAs‐II). Moreover, "noncovalently conformational locks", are used as an effective strategy to enhance the rigidity and planarity of NREAs and improve device performance. Herein, a novel series of NREAs‐II (PhO4T‐1, PhO4T‐2, and PhO4T‐3) is constructed as a valuable platform for exploring the impact of the end group engineering on optoelectronic properties, intermolecular packing behaviors, and device performance. As a result, a high power conversion efficiency of 13.76% is achieved for PhO4T‐3 based OSCs, which is much higher than those of the PhO4T‐1 and PhO4T‐2‐based devices. Compared with several representative FREAs, PhO4T‐3 possesses the highest figure‐of‐merit value of 133.45 based on a cost‐efficiency evaluation. This work demonstrates that the simple‐structured NREAs‐II are promising candidates for low‐cost and high‐performance OSCs. [ABSTRACT FROM AUTHOR]

Three nonfused ring electron acceptors (NFREAs; 2Th‐2F, BTh‐Th‐2F, and 2BTh‐2F) with thieno[3,2‐b]thiophene bearing two bis(4‐butylphenyl)amino substituents as the core, 3‐octylthiophene or 3‐octylthieno[3,2‐b]thiophene as the spacer, and 3‐(1,1‐dicyanomethylene)‐5,6‐difluoro‐1‐indanone as the terminal group are designed and synthesized. The molar extinction coefficient of acceptors and the electron mobility of blend films gradually increase with increasing π‐conjugation length. Moreover, 2BTh‐2F displays a planar molecular conformation assisted by S···N and S···O intramolecular interactions. More importantly, the molecular stacking changes from 2D packing for the 2Th‐2F analog to 3D network packing for 2BTh‐2F. Due to these comprehensive merits, 2BTh‐2F:PBDB‐T‐based organic solar cells give a high power conversion efficiency of 14.53%. More impressively, when D18 is used as the donor polymer, the power conversion efficiency is further enhanced to 15.44%, which is the highest value reported for solar cells based on NFREAs. [ABSTRACT FROM AUTHOR]

We developed a series of highly crystalline double‐cable conjugated polymers for application in single‐component organic solar cells (SCOSCs). These polymers contain conjugated backbones as electron donor and pendant perylene bisimide units (PBIs) as electron acceptor. PBIs are connected to the backbone via alkyl units varying from hexyl (C6H12) to eicosyl (C20H40) as flexible linkers. For double‐cable polymers with short linkers, the PBIs tend to stack in a head‐to‐head fashion, resulting in large d‐spacings (e.g. 64 Å for the polymer P12 with C12H24 linker) along the lamellar stacking direction. When the length of the linker groups is longer than a certain length, the PBIs instead adopt a more ordered packing likely via H‐aggregation, resulting in short d‐spacings (e.g. 50 Å for the polymer P16 with C16H32 linker). This work highlights the importance of linker length on the molecular packing of the acceptor units and the influences on the photovoltaic performance of SCOSCs. [ABSTRACT FROM AUTHOR]

We developed a series of highly crystalline double‐cable conjugated polymers for application in single‐component organic solar cells (SCOSCs). These polymers contain conjugated backbones as electron donor and pendant perylene bisimide units (PBIs) as electron acceptor. PBIs are connected to the backbone via alkyl units varying from hexyl (C6H12) to eicosyl (C20H40) as flexible linkers. For double‐cable polymers with short linkers, the PBIs tend to stack in a head‐to‐head fashion, resulting in large d‐spacings (e.g. 64 Å for the polymer P12 with C12H24 linker) along the lamellar stacking direction. When the length of the linker groups is longer than a certain length, the PBIs instead adopt a more ordered packing likely via H‐aggregation, resulting in short d‐spacings (e.g. 50 Å for the polymer P16 with C16H32 linker). This work highlights the importance of linker length on the molecular packing of the acceptor units and the influences on the photovoltaic performance of SCOSCs. [ABSTRACT FROM AUTHOR]

In this work, we successfully applied a fullerene derivative PC 71 BM as the second acceptor in PM6:BTP-BO-4Cl bulk heterojunction organic solar cell system. The device performance can be remarkably enhanced from 16.65% of the PM6:BTP-BO-4Cl binary system to approaching 17.4% of the ternary system with just low PC 71 BM loading. Detailed investigation revealed that introduction of small amount of PC 71 BM can improve the molecular aggregation and film morphology, thus display better exciton dissociation and charge transport. [Display omitted] In this work, we introduced a fullerene acceptor (PC 71 BM) into the binary photo-active layer based on a polymer donor (PM6) and a non-fullerene small molecular acceptor (BTP-BO-4Cl), and as a consequence, the ternary organic solar cells realized a high-power conversion efficiency of 17.39% compared to 16.65% in binary solar cells. The performance enhancement was found to be due to the optimized morphology and hence balanced hole and electron mobilities, which is responsible for the suppressed charge recombination and hence high photocurrent in solar cells. In addition, PC 71 BM shows the complementary absorption with PM6 and BTP-BO-4Cl, which can broaden the absorption range of the photo-active layer and hence more photons from the sunlight can be utilized. Besides, PC 71 BM shows the cascade energy level alignment between PM6 and BTP-BO-4Cl, which is helpful for charge transfer from donor to acceptor. All these merits explain the high performance in ternary solar cells, and also demonstrate that ternary photovoltaics adopting non-fullerene acceptor with the fullerene acceptor as small amount of additive is an efficient strategy to gain high performing organic solar cells. [ABSTRACT FROM AUTHOR]

A series of conjugated polymers containing benzodithiophene as donor and isoindigo as acceptor with no, one, two and three thiophene spacer groups is synthesized and characterized. The polymer with bithiophene as a spacer has a superior efficiency of 7.31% in solar cells. This demonstrates an important design strategy to produce polymers for high‐performance solar cells by inserting thiophene spacer groups. [ABSTRACT FROM AUTHOR]

Bimolecular charge carrier recombination in blends of a conjugated copolymer based on a thiophene and quinoxaline (TQ1) with a fullerene derivative ((6,6)-phenyl-C71-butyric acidmethyl ester, PC71BM) is studied by two complementary techniques. TRMC (time-resolved microwave conductance) monitors the conductance of photogenerated mobile charge carriers locally on a timescale of nanoseconds, while using photo-CELIV (charge extraction by linearly increasing voltage) charge carrier dynamics are monitored on a macroscopic scale and over tens of microseconds. Despite these significant differences in the length and time scales, both techniques show a reduced Langevin recombination with a prefactor ζ close to 0.05. For TQ1:PC71BM blends, the ζ value is independent of temperature. On comparing TRMC data with electroluminescence measurements it is concluded that the encounter complex and the charge transfer state have very similar energetic properties. The ζ value for annealed poly(3-hexylthiophene) (P3HT):(6,6)-phenyl-C61-butyric acid methyl ester (PC61BM) is approximately 10−4, while for blend systems containing an amorphous polymer ζ values are close to 1. These large differences can be related to the extent of charge delocalization of opposite charges in an encounter complex. Insight is provided into factors governing the bimolecular recombination process, which forms a major loss mechanism limiting the efficiency of polymer solar cells. [ABSTRACT FROM AUTHOR]

Three asymmetric non‐fullerene acceptors (LL2, LL3, and LL4) are designed and synthesized with one norbornyl‐modified 1,1‐dicyanomethylene‐3‐indanone (CBIC) terminal group and one chlorinated 1,1‐dicyanomethylene‐3‐indanone (IC‐2Cl) terminal group. The three‐dimensional shape‐persistent CBIC terminal group can effectively enhance the solubility and tune the packing mode of acceptors. Compared with their symmetric counterparts (LL2‐2Cl, LL3‐2Cl, and LL4‐2Cl) bearing two IC‐2Cl terminals, the asymmetric acceptors show improved solubilities, giving rise to enhanced crystallinity and favored nanomorphology for charge transport in the blend films with PBDB‐T. Asymmetric acceptors based organic solar cells (OSCs) also show much lower voltage loss due to their higher ECT and EQEEL values. Therefore, they exhibit 17−27% higher power conversion efficiency (PCE) than OSCs based on the corresponding symmetric acceptors. Among these six acceptors, LL3 with a central benzotriazole core shows the best PCE of 16.82% with an outstanding Jsc of 26.97 mA cm−2 and a low nonradiative voltage loss (ΔVnr) of 0.18 V, the best values for PBDB‐T based OSCs. The Jsc and ΔVnr also represent the best reported for asymmetric non‐fullerene acceptors‐based OSCs to date. The results demonstrate that the combination of the unique CBIC terminal group with the asymmetric strategy is a promising way to enhance the performance of OSCs. [ABSTRACT FROM AUTHOR]

Morphology evolution kinetics at multi‐scale regime is a challenging problem which is critical for industrial fabrication of high‐performance organic solar cells (OSCs). An innovative strategy utilizing a patterned blade to print non‐fullerene (NF) based devices in ambient conditions is demonstrated. A specially designed patterned blade with micro‐cylinder arrays exhibit a reasonable control over the fluid flow at high extensional and shear strain rate to enhance lateral mass transport during blade‐coating. Comparison of patterned and normal blade in printing polymer:NF blend film at different speeds reveals interesting avenues to optimize the blend films morphology. Patterned blade printed PM6:Y6 films yield a PCE of 15.93% as compared to 14.55% from a normal blade. Through in situ and ex situ morphology characterization techniques, the use of patterned blades induce conformational changes in PM6 chains, enabling Y6 to crystallize faster and more efficiently. Such improved blend morphology enables favorable charge transfer and transport to realize superior device performance. A lower stick‐slip effect at the macro‐scale with the patterned blade results in a smoother film promoting device reproducibility. Applications in efficient large‐scale devices, confirming the choice of patterned blade design are reported. The efforts collaborating device engineering, morphology evolution kinetics would enable reproducibility and eased commercialization of OSCs at large scale. [ABSTRACT FROM AUTHOR]

[Display omitted] • A pair of novel metal-free chiral molecular ferroelectric semiconductors was prepared. • Construction of narrow band gap structures by introducing polyiodide anions. • Designing ferroelectrics with helical arrangement by chiral chemical means. • The initial application in photovoltaics is demonstrated. Ferroelectric semiconductors have gained significant attraction for designing photovoltaic devices. However, their wide bandgap results in poor absorption of visible light. Herein, we report a pair of chiral metal-free molecular ferroelectric semiconductors (1 R ,4 R /1 S ,4 S - C 5 H 10 NO)I 3 (R/S-OABHI ; (1 R ,4 R /1 S ,4 S - C 5 H 10 NO)+ = 1 R ,4 R /1 S ,4 S -2-oxa-5-azabicyclo[2.2.1]heptonium) with notable ferroelectricity (saturation polarization of ∼6.8 and 6.1 μC/cm2 for R-/S-OABHI , respectively). They demonstrate an appropriate photovoltaic bandgap of ∼ 1.41 and 1.39 eV for R-/S-OABHI , respectively, comparable to MAPbI 3 (MA = methylammonium). Experiments and computational simulations reveal that the ferroelectricity of R / S-OABHI originates from their non-centrosymmetric crystal packing in a controllable helical manner, while the I 3 − contributes to band edges. Meanwhile, photovoltaic effect is firstly observed in the R-OABHI based solar cell with an open-circuit voltage of 0.581 V and a short-circuit current density of 1.734 mA/cm2. Overall, we establish a new approach for realizing metal-free ferroelectric photovoltaics, and it will pave the way for the exploration of multifunctional chiral molecular ferroelectrics. [ABSTRACT FROM AUTHOR]

Fused‐ring electron acceptors have made significant progress in recent years, while the development of fully non‐fused ring acceptors has been unsatisfactory. Here, two fully non‐fused ring acceptors, o‐4TBC‐2F and m‐4TBC‐2F, were designed and synthesized. By regulating the location of the hexyloxy chains, o‐4TBC‐2F formed planar backbones, while m‐4TBC‐2F displayed a twisted backbone. Additionally, the o‐4TBC‐2F film showed a markedly red‐shifted absorption after thermal annealing, which indicated the formation of J‐aggregates. For fabrication of organic solar cells (OSCs), PBDB‐T was used as a donor and blended with the two acceptors. The o‐4TBC‐2F‐based blend films displayed higher charge mobilities, lower energy loss and a higher power conversion efficiency (PCE). The optimized devices based on o‐4TBC‐2F gave a PCE of 10.26 %, which was much higher than those based on m‐4TBC‐2F at 2.63 %, and it is one of the highest reported PCE values for fully non‐fused ring electron acceptors. [ABSTRACT FROM AUTHOR]

Fused‐ring electron acceptors have made significant progress in recent years, while the development of fully non‐fused ring acceptors has been unsatisfactory. Here, two fully non‐fused ring acceptors, o‐4TBC‐2F and m‐4TBC‐2F, were designed and synthesized. By regulating the location of the hexyloxy chains, o‐4TBC‐2F formed planar backbones, while m‐4TBC‐2F displayed a twisted backbone. Additionally, the o‐4TBC‐2F film showed a markedly red‐shifted absorption after thermal annealing, which indicated the formation of J‐aggregates. For fabrication of organic solar cells (OSCs), PBDB‐T was used as a donor and blended with the two acceptors. The o‐4TBC‐2F‐based blend films displayed higher charge mobilities, lower energy loss and a higher power conversion efficiency (PCE). The optimized devices based on o‐4TBC‐2F gave a PCE of 10.26 %, which was much higher than those based on m‐4TBC‐2F at 2.63 %, and it is one of the highest reported PCE values for fully non‐fused ring electron acceptors. [ABSTRACT FROM AUTHOR]

A record power conversion efficiency of 8.40 % was obtained in single‐component organic solar cells (SCOSCs) based on double‐cable conjugated polymers. This is realized based on exciton separation playing the same role as charge transport in SCOSCs. Two double‐cable conjugated polymers were designed with almost identical conjugated backbones and electron‐withdrawing side units, but extra Cl atoms had different positions on the conjugated backbones. When Cl atoms were positioned at the main chains, the polymer formed the twist backbones, enabling better miscibility with the naphthalene diimide side units. This improves the interface contact between conjugated backbones and side units, resulting in efficient conversion of excitons into free charges. These findings reveal the importance of charge generation process in SCOSCs and suggest a strategy to improve this process: controlling miscibility between conjugated backbones and aromatic side units in double‐cable conjugated polymers. [ABSTRACT FROM AUTHOR]

A record power conversion efficiency of 8.40 % was obtained in single‐component organic solar cells (SCOSCs) based on double‐cable conjugated polymers. This is realized based on exciton separation playing the same role as charge transport in SCOSCs. Two double‐cable conjugated polymers were designed with almost identical conjugated backbones and electron‐withdrawing side units, but extra Cl atoms had different positions on the conjugated backbones. When Cl atoms were positioned at the main chains, the polymer formed the twist backbones, enabling better miscibility with the naphthalene diimide side units. This improves the interface contact between conjugated backbones and side units, resulting in efficient conversion of excitons into free charges. These findings reveal the importance of charge generation process in SCOSCs and suggest a strategy to improve this process: controlling miscibility between conjugated backbones and aromatic side units in double‐cable conjugated polymers. [ABSTRACT FROM AUTHOR]

Sequential deposition has great potential to achieve high performance in organic solar cells due to the resulting well‐controlled vertical phase separation. In this work, double bulk heterojunction organic solar cells are fabricated by sequential‐blade cast in ambient conditions. Probed by the in situ grazing incidence X‐ray diffraction and in situ UV–vis absorption measurements, the seq‐blade system exhibits a different tendency from each of the binary films during the film formation process. Due to the extensive aggregation of FOIC, the binary PBDB‐T:FOIC film displays a strong and large phase separation, resulting in low current density (Jsc) and unsatisfactory power conversion efficiency. In the seq‐blade cast system, the bottom layer PBDB‐T:IT‐M produces many crystal nuclei for the top layer PBDB‐T:FOIC, so the PBDB‐T molecules are able to crystallize easily and quickly. Balanced crystallization kinetics between polymer and small molecule and an ideal percolation network in the film are observed. In addition, the balanced crystallization kinetics are favorable toward realizing lower recombination loss through charge transport processes. [ABSTRACT FROM AUTHOR]

Single‐layered organic solar cells (OSCs) using nonfullerene acceptors have reached 16% efficiency. Such a breakthrough has inspired new sparks for the development of the next generation of OSC materials. In addition to the optimization of electronic structure, it is important to investigate the essential solid‐state structure that guides the high efficiency of bulk heterojunction blends, which provides insight in understanding how to pair an efficient donor–acceptor mixture and refine film morphology. In this study, a thorough analysis is executed to reveal morphology details, and the results demonstrate that Y6 can form a unique 2D packing with a polymer‐like conjugated backbone oriented normal to the substrate, controlled by the processing solvent and thermal annealing conditions. Such morphology provides improved carrier transport and ultrafast hole and electron transfer, leading to improved device performance, and the best optimized device shows a power conversion efficiency of 16.88% (16.4% certified). This work reveals the importance of film morphology and the mechanism by which it affects device performance. A full set of analytical methods and processing conditions are executed to achieve high efficiency solar cells from materials design to device optimization, which will be useful in future OSC technology development. [ABSTRACT FROM AUTHOR]

The crystalline cooperativity of the donor and acceptor segment in double‐cable conjugated polymers plays an important role in the nanophase separation and photovoltaic performance in single‐component organic solar cells (SCOSCs). Two double‐cable conjugated polymers with the same conjugated backbone and perylene bisimide (PBI) side units were designed in which PBIs were positioned symmetrically and perpendicularly (P1) and asymmetrically and slantingly (P2) along the conjugated backbones. After thermal annealing, both conjugated backbones and PBI side units in P1 tend to form ordered nanostructures, while PBI side units in P2 dominated the crystallization and hamper the crystallization of conjugated backbones. P1 showed good crystalline cooperativity between conjugated backbones and PBI side units, resulting in improved power conversion efficiencies (PCEs) up to 3.43 % in SCOSCs, while P2 with poor crystalline cooperativity exhibited PCEs below 2.42 %. [ABSTRACT FROM AUTHOR]

The crystalline cooperativity of the donor and acceptor segment in double‐cable conjugated polymers plays an important role in the nanophase separation and photovoltaic performance in single‐component organic solar cells (SCOSCs). Two double‐cable conjugated polymers with the same conjugated backbone and perylene bisimide (PBI) side units were designed in which PBIs were positioned symmetrically and perpendicularly (P1) and asymmetrically and slantingly (P2) along the conjugated backbones. After thermal annealing, both conjugated backbones and PBI side units in P1 tend to form ordered nanostructures, while PBI side units in P2 dominated the crystallization and hamper the crystallization of conjugated backbones. P1 showed good crystalline cooperativity between conjugated backbones and PBI side units, resulting in improved power conversion efficiencies (PCEs) up to 3.43 % in SCOSCs, while P2 with poor crystalline cooperativity exhibited PCEs below 2.42 %. [ABSTRACT FROM AUTHOR]

• Acceptor fluorination leads to increased voltage losses in organic solar cells. • The increased voltage loss is associated with increased reorganization energy. • A side chain modification strategy is proposed to address the voltage loss issue. Acceptor fluorination is a commonly employed molecular modification strategy aimed at enhancing the quantum efficiency and charge carrier transport properties of organic solar cells. However, this approach often leads to a significant reduction in the open-circuit voltage (V oc) of the solar cells, thereby limiting their overall performance. In this study, we investigate the limitation of V oc in organic solar cells based on fluorinated acceptors. Our investigation reveals that the reduced V oc can be attributed to increased voltage losses (V loss), primarily arising from more significant non-radiative voltage losses originating from a decline in the external quantum efficiency of electroluminescence (EQE EL). Furthermore, we establish that the reduced EQE EL is a result of deteriorated molecular packing, which leads to an elevated reorganization energy. To address the high V loss and limited performance observed in solar cells utilizing fluorinated acceptors, we propose a strategy involving acceptor side-chain modifications. These results provide new insights into enhancing the performance of organic solar cells. [ABSTRACT FROM AUTHOR]

• Increasing donor side chain size leads to reduced CT dissociation efficiency. • Increasing acceptor side chain size results in reduced device voltage losses. • Highest PCE is realized when both the donor and acceptor are with large side chains. Increasing the size of the side chains of the donor or the acceptor materials is a highly effective strategy to reduce voltage losses, and increase the open-circuit voltage (Voc) of organic solar cells (OSCs). However, higher Voc does not necessarily translate to improved overall performance. To optimize side-chains and improve the performance of OSCs, the origin of the impact of the increased size of the donor and/or acceptor side side-chains size on the performance of OSCs is investigated. The study demonstrates that increasing the size of donor side chains can increase Voc, but it can also lead to deteriorated molecular packing, limiting overall solar cell performance. On the other hand, increasing the size of acceptor side chains can also increase Voc and improve molecular packing properties of the active layer, resulting in improved solar cell performance. Finally, the study shows that the best photovoltaic performance is achieved when both the donor and acceptor have large side chains. This research establishes the relationship between side chains of active materials, molecular packing properties, and the energetics of the donor/acceptor active layer, which is crucial for overcoming performance bottlenecks in OSCs. [ABSTRACT FROM AUTHOR]

A new nonfused ring electron acceptor PDI-DO-2F is designed and synthesized by attaching perylenediimide (PDI) unit as a pendent group to the central donor core. Compared with the control molecule DO-2F , the introduction of PDI lateral substituent can greatly enhance the solubility and decrease the crystallinity of the resulted acceptor. The PBDB-T :PDI-DO-2F blend film exhibits a much better morphology with higher and more balanced carrier mobility in contrast to PBDB-T :DO-2F one. PDI-DO-2F based organic solar cells (OSCs) give a power conversion efficiency (PCE) of 11.78%, higher than DO-2F based ones (9.82%). Furthermore, PDI-DO-2F based OSCs shows a Δ E non-rad value of 0.23 eV, which is significantly lower than the DO-2F based ones (0.28 eV). More importantly, the addition of PDI-DO-2F as the third component to the PBDB-T :DO-2F binary system can optimize the morphology of blend films and improve the shelf stability of devices. And the PBDB-T :DO-2F : PDI-DO-2F based ternary OSCs achieve a higher PCE of 13.82%. [Display omitted] • A new nonfused ring electron acceptor is designed and synthesized. • PDI unit as a pendent group can greatly enhance the solubility and decrease the crystallinity of the acceptor. • Significantly different power conversion efficiencies of 9.82%, 11.78% and 13.82% are achieved. [ABSTRACT FROM AUTHOR]

[Display omitted] • Three small molecular acceptors were designed and synthesized. • Noncovalent Conformational Locks and Side-Chain Engineering can adjust the properties of acceptors. • Significantly different power conversion efficiencies of 12.09%, 12.30% and 14.25% are achieved. Three novel small molecular acceptors (SMAs) BO-2F , BO-C8-2F and BO-C2C6-C8-2F were designed and synthesized. These acceptors all possess planar molecular backbone because of the introduction of intramolecular noncovalent interaction. Among them, BO-C2C6-C8-2F with four side chains, which has the highest solubility, can form more appropriate nanomorphology when blending with PBDB-T. Hence, organic solar cells (OSCs) based on PBDB-T: BO-C2C6-C8-2F displayed an outstanding power convesion efficiency (PCE) of 14.25%, which is higher than BO-2F and BO-C8-2F based ones. To the best of our knowledge, the PCE of 14.25% is one of the highest for the OSCs based on A-π-D-π-A type SMAs. Our results have demonstrated that the combination of side-chain engineering and intramolecular conformation lock has a great prospect in the design of high performance SMAs for OSCs. [ABSTRACT FROM AUTHOR]

• Minor terminal and central changes endow DO-2F and FO-N complementary absorption. • Asymmetrical FO-N effectively suppress the self-aggregation of DO-2F. • Acceptor alloy is found between the FO-N and DO-2F. • Alloy state acceptors produce suitable morphology with reduced V nr of 0.23 eV. • FO-N is an excellent third component for highly efficient OSCs of 14.10% Nonfused ring acceptors have shown great potential for future commercial applications of organic solar cells (OSCs) due to their simple structure and low synthetic costs. Herein, a novel asymmetrical nonfused ring acceptor FO-N with one branched lateral chain and one fluoro substituent at the central phenylene core was designed and introduced into PBDB-T : DO-2F binary system to fabricate high-efficiency ternary OSCs. The high-lying LUMO level of FO-N is conducive to improve V oc for ternary devices. More importantly, the introduction of FO-N as the third component can efficiently improve the compatibility of the ternary system via tuning the crystal size and optimizing the blend film morphology, which is beneficial to charge separation and reduced the non-radiative energy loss (Δ E nonrad). Finally, the ternary device achieved a low Δ E nonrad of 0.23 eV and a greatly improved PCE of 14.10% and with a V oc of 0.88 V, a J sc of 21.48 mA/cm2 and an FF of 74.41%. These results imply that the asymmetric nonfused ring acceptor design strategy is an effective way for optimizing the photovoltaic performance of highly crystallized blend system. [ABSTRACT FROM AUTHOR]

The surface defects of solution-processed ZnO films lead to various intragap states. When the solution-processed ZnO films are used as electron transport interlayers (ETLs) in inverted organic solar cells, the intragap states act as interfacial recombination centers for photogenerated charges and thereby degrade the device performance. Here, a simple passivation method based on ethanedithiol (EDT) treatment is demonstrated, which effectively removes the surface defects of the ZnO nanocrystal films by forming zinc ethanedithiolates. The passivation by EDT treatment modulates the intragap states of the ZnO films and introduces a new intragap band. When the EDT-treated ZnO nanocrystal films are used as ETLs in inverted organic solar cells, both the power conversion efficiency and stability of the devices are improved. The control studies show that the solar cells with EDT-treated ZnO films exhibit reduced charge recombination rates and enhanced charge extraction properties. These features are consistent with the fact that the modulation of the intragap states results in reduction of interfacial recombination as well as the improved charge selectivity and electron transport properties of the ETLs. It is further demonstrated that the EDT treatment-based passivation method can be extended to ZnO films deposited from sol-gel precursors. [ABSTRACT FROM AUTHOR]

Photoexcitation of conjugated polymer–fullereneblends resultsin population of a local charge transfer (CT) state at the interfacebetween the two materials. The competition between recombination anddissociation of this interfacial state limits the generation of fullyseparated free charges. Therefore, a detailed understanding of theCT states is critical for building a comprehensive picture of theorganic solar cells operation. We applied a new fluorescence microscopymethod called two-dimensional polarization imaging to gain insightinto the orientation of the transition dipole moments of the CT states,and the associated excitation energy transfer processes in TQ1:PCBMblend films. The polymer phase was oriented mechanically to relatethe polymer dipole moment orientation to that of the CT states. CTstate formation was observed to be much faster than energy transferin the polymer phase. However, after being formed an emissive CT statedoes not exchange excitation energy with other CT states, suggestingthat they are spatially and/or energetically isolated. We found thatthe quantum yield of the CT emission is smaller for CT states spatiallylocated in the highly oriented polymer domains, which is interpretedas the result of enhanced CT state dissociation in highly orderedstructures. [ABSTRACT FROM AUTHOR]

Based on the flexibility of polymer film, cone-shaped polymer solar cells (PSCs) are fabricated and studied. Effective light trapping is achieved due to multi-absorption in all 360° directions. Monte Carlo ray tracing is used to simulate the absorption of cone-shaped PSCs with two variables: wavelength and half cone angle. With an inverted indium-tin-oxide-free device structure, a 43% enhanced light utilization without loss of material utilization is realized in the cone-shaped PSCs with a half cone angle of 45°, compared with the planar PSCs. [ABSTRACT FROM AUTHOR]

A series of alkyl, alkoxyl, and alkylthio substituted A–π–D–π–A type nonfullerene acceptors (NFAs) IDTCN‐C, IDTCN‐O, and IDTCN‐S are designed and synthesized. The introduction of a lateral side chain at the outer position of the π bridge unit can endow the terminal moiety with a confined planar conformation due to the steric hindrance. Thus, compared with nonsubstituted NFA (IDTT2F), these acceptors tend to form favorable face‐on orientation and exhibit strong crystallinity as verified with grazing‐incidence wide‐angle X‐ray scattering measurement. Moreover, the variation of side chain can significantly change the lowest unoccupied molecular orbital (LUMO) energy level of acceptors. As state‐of‐the‐art NFAs, a power conversion efficiency of 13.28% (Voc = 0.91 V, Jsc = 19.96 mA cm−2, and FF = 73.2%) is obtained for the as‐cast devices based on IDTCN‐O, which is among the highest value reported in literature. The excellent photovoltaic performance for IDTCN‐O can be attributed to its slightly up‐shifted LUMO level and more balanced charge transport. This research demonstrates side chain engineering is an effective way to achieve high efficiency organic solar cells. [ABSTRACT FROM AUTHOR]