Green‐Solvent‐Processed All‐Polymer Solar Cells Containing a Perylene Diimide‐Based Acceptor with an Efficiency over 6.5%

To realize high power conversion efficiencies (PCEs) in green‐solvent‐processed all‐polymer solar cells (All‐PSCs), a long alkyl chain modified perylene diimide (PDI)‐based polymer acceptor PPDIODT with superior solubility in nonhalogenated solvents is synthesized. A properly matched PBDT‐TS1 is selected as the polymer donor due to the red‐shifted light absorption and low‐lying energy level in order to achieve the complementary absorption spectrum and matched energy level between polymer donor and polymer acceptor. By utilizing anisole as the processing solvent, an optimal efficiency of 5.43% is realized in PBDT‐TS1/PPDIODT‐based All‐PSC with conventional configuration, which is comparable with that of All‐PSCs processed by the widely used binary solvent. Due to the utilization of an inverted device configuration, the PCE is further increased to over 6.5% efficiency. Notably, the best‐performing PCE of 6.58% is the highest value for All‐PSCs employing PDI‐based polymer acceptors and green‐solvent‐processed All‐PSCs. The excellent photovoltaic performance is mainly attributed to a favorable vertical phase distribution, a higher exciton dissociation efficiency (P_diss) in the blend film, and a higher electrode carrier collection efficiency. Overall, the combination of rational molecular designing, material selection, and device engineering will motivate the efficiency breakthrough in green‐solvent‐processed All‐PSCs.     

Improvement of Photovoltaic Performance of Polymer Solar Cells by Rational Molecular Optimization of Organic Molecule Acceptors

Two n‐type organic semiconductor (n‐OS) small molecules m‐ITIC‐2F and m‐ITIC‐4F with fluorinated 2‐(2,3‐dihydro‐3‐oxo‐1H‐inden‐1‐ylidene)propanedinitrile (IC) terminal moieties are prepared, for the application as an acceptor in polymer solar cells (PSCs), to further improve the photovoltaic performance of the n‐OS acceptor 3,9‐bis(2‐methylene‐(3‐(1,1‐dicyanomethylene) indanone) ‐5,5,11,11‐tetrakis(3‐hexylphenyl)‐dithieno[2,3‐d:2′,3′‐d′]‐sindaceno[1,2‐b:5,6‐b′]‐dithiophene (m‐ITIC). Compared to m‐ITIC, these two new acceptors show redshifted absorption, higher molecular packing order, and improved electron mobilities. The power conversion efficiencies (PCE) of the as‐cast PSCs with m‐ITIC‐2F or m‐ITIC‐4F as an acceptor and a low‐cost donor–acceptor (D–A) copolymer PTQ10 as a donor reach 11.57% and 11.64%, respectively, which are among the highest efficiency for the as‐cast PSCs so far. Furthermore, after thermal annealing treatment, improved molecular packing and enhanced phase separation are observed, and the higher PCE of 12.53% is achieved for both PSCs based on the two acceptors. The respective and unique advantage with the intrinsic high degree of order, molecular packing, and electron mobilities of these two acceptors will be suitable to match with different p‐type organic semiconductor donors for higher PCE values, which provide a great potential for the PSCs commercialization in the near future. These results indicate that rational molecular structure optimization is of great importance to further improve photovoltaic properties of the photovoltaic materials.     

All‐Polymer Solar Cells with over 12% Efficiency and a Small Voltage Loss Enabled by a Polymer Acceptor Based on an Extended Fused Ring Core

Although the field of all‐polymer solar cells (all‐PSCs) has seen rapid progress in device efficiencies during the past few years, there are limited choices of polymer acceptors that exhibit strong absorption in the near‐IR region and achieve high open‐circuit voltage (V_OC) at the same time. In this paper, an all‐PSC device is demonstrated with a 12.06% efficiency based on a new polymer acceptor (named PT‐IDTTIC) that exhibits strong absorption (maximum absorption coefficient: 2.41 × 10⁵ cm^?1) and a narrow optical bandgap (1.49 eV). Compared to previously reported polymer acceptors such as those based on the indacenodithiophene (IDT) core, the indacenodithienothiophene (IDTT) core has further extended fused ring, providing the polymer with extended absorption into the near‐IR region and also increases the electron mobility of the polymer. By blending PT‐IDTTIC with the donor polymer, PM6, a high‐efficiency all‐PSC is achieved with a small voltage loss of 0.52 V, without sacrificing J_SC and FF, which demonstrates the great potential of high‐performance all‐PSCs.     

Effect of Molecular Orientation of Donor Polymers on Charge Generation and Photovoltaic Properties in Bulk Heterojunction All‐Polymer Solar Cells

All‐polymer solar cells (all‐PSCs) utilizing p‐type polymers as electron‐donors and n ‐typepolymers as electron‐acceptors have attracted a great deal of attention, and their efficiencies have been improved considerably. Here, five polymer donors with different molecular orientations are synthesized by random copolymerization of 5‐fluoro‐2,1,3‐benzothiadiazole with different relative amounts of 2,2′‐bithiophene (2T) and dithieno[3,2‐b;2′,3′‐d]thiophene (DTT). Solar cells are prepared by blending the polymer donors with a naphthalene diimide‐based polymer acceptor (PNDI) or a [6,6]‐phenyl C₇₁‐butyric acid methyl ester (PC₇₁BM) acceptor and their morphologies and crystallinity as well as optoelectronic, charge‐transport and photovoltaic properties are studied. Interestingly, charge generation in the solar cells is found to show higher dependence on the crystal orientation of the donor polymer for the PNDI‐based all‐PSCs than for the conventional PC₇₁BM‐based PSCs. As the population of face‐on‐oriented crystallites of the donor increased in PNDI‐based PSC, the short‐circuit current density (J_SC) and external quantum efficiency of the devices are found to significantly improve. Consequently, device efficiency was enhanced of all‐PSC from 3.11% to 6.01%. The study reveals that producing the same crystal orientation between the polymer donor and acceptor (face‐on/face‐on) is important in all‐PSCs because they provide efficient charge transfer at the donor/acceptor interface.     

Facile Synthesis of Polycyclic Aromatic Hydrocarbon (PAH)–Based Acceptors with Fine‐Tuned Optoelectronic Properties: Toward Efficient Additive‐Free Nonfullerene Organic Solar Cells

A series of polycyclic aromatic hydrocarbons (PAHs) with extended π‐conjugated cores (from naphthalene, anthracene, pyrene, to perylene) are incorporated into nonfullerene acceptors for the first time. Four different fused‐ring electron acceptors (FREAs), i.e., DTN‐IC‐2Ph , DTA‐IC‐3Ph , DTP‐IC‐4Ph , and DTPy‐IC‐5Ph , are prepared via simple and facile synthetic procedures, yielding a remarkable platform to study the structure–property relationship for nonfullerene solar cells. With the PAH core being extended systematically, the gradually redshifted absorption with enhanced molar extinction coefficient (ε) is realized, the energy level of the highest occupied molecular orbital is up‐shifted, and the electron mobility is greatly enhanced. Meanwhile, the solubility decreases and the molecular packing becomes strengthened. As a result, with an optimized combination of these characteristics, DTP‐IC‐4Ph attains good solubility, high molar extinction coefficient, complementary absorption, suitable morphology, well‐matched energy levels, as well as efficient charge dissociation and transport in blend film. Consequently, the DTP‐IC‐4Ph ‐based solar cells with a donor polymer, poly[(2,6‐(4,8‐bis(5‐(2‐ethylhexyl)thiophen‐2‐yl)‐benzo[1,2‐b:4,5‐b′]dithiophene))‐alt‐(5,5‐(1′,3′‐di‐2‐thienyl‐5′,7′‐bis(2‐ethylhexyl)benzo[1′,2′‐c:4′,5′‐c′]dithiophene‐4,8‐dione))] (PBDB‐T) exhibit a promising power conversion efficiency of 10.37% without any additives, which is close to the best performance achieved in additive‐free nonfullerene solar cells (NFSCs). The results demonstrate that the PAH building blocks have great potential for the construction of novel FREAs for efficient additive‐free NFSCs.     

Design of Cyanovinylene‐Containing Polymer Acceptors with Large Dipole Moment Change for Efficient Charge Generation in High‐Performance All‐Polymer Solar Cells

Designing polymers that facilitate exciton dissociation and charge transport is critical for the production of highly efficient all‐polymer solar cells (all‐PSCs). Here, the development of a new class of high‐performance naphthalenediimide (NDI)‐based polymers with large dipole moment change (Δµ_ge) and delocalized lowest unoccupied molecular orbital (LUMO) as electron acceptors for all‐PSCs is reported. A series of NDI‐based copolymers incorporating electron‐withdrawing cyanovinylene groups into the backbone (PNDITCVT‐R) is designed and synthesized with 2‐hexyldecyl (R = HD) and 2‐octyldodecyl (R = OD) side chains. Density functional theory calculations reveal an enhancement in Δµ_ge and delocalization of the LUMO upon the incorporation of cyanovinylene groups. All‐PSCs fabricated from these new NDI‐based polymer acceptors exhibit outstanding power conversion efficiencies (7.4%) and high fill factors (65%), which is attributed to efficient exciton dissociation, well‐balanced charge transport, and suppressed monomolecular recombination. Morphological studies by grazing X‐ray scattering and resonant soft X‐ray scattering measurements show the blend films containing polymer donor and PNDITCVT‐R acceptors to exhibit favorable face‐on orientation and well‐mixed morphology with small domain spacing (30–40 nm).     

3,4‐Dicyanothiophene—a Versatile Building Block for Efficient Nonfullerene Polymer Solar Cells

In this contribution, a versatile building block, 3,4‐dicyanothiophene (DCT), which possesses structural simplicity and synthetic accessibility for constructing high‐performance, low‐cost, wide‐bandgap conjugated polymers for use as donors in polymer solar cells (PSCs), is reported. A prototype polymer, PB3TCN‐C66, and its cyano‐free analogue polymer PB3T‐C66, are synthesized to evaluate the potential of using DCT in nonfullerene PSCs. A stronger aggregation property in solution, higher thermal transition temperatures with higher enthalpies, a larger dipole moment, higher relative dielectric constant, and more linear conformation are exhibited by PB3TCN‐C66. Solar cells employing IT‐4F as the electron acceptor offer power conversion efficiencies (PCEs) of 11.2% and 2.3% for PB3TCN‐C66 and PB3T‐C66, respectively. Morphological characterizations reveal that the PB3TCN‐C66:IT‐4F blend exhibits better π–π paracrystallinity, a contracted domain size, and higher phase purity, consistent with its higher molecular interaction parameter, derived from thermodynamic calculations. Moreover, PB3TCN‐C66 offers a higher open‐circuit voltage and reduced energy loss than most state‐of‐the‐art wide‐bandgap polymers, without the need of additional electron‐withdrawing substituents. Two additional polymers derived from DCT also demonstrate promising performance with a higher PCE of 13.4% being achieved. Thus, DCT represents a versatile and promising building block for constructing high‐performance, low‐cost, conjugated polymers for application in PSCs.     

Side‐Chain Impact on Molecular Orientation of Organic Semiconductor Acceptors: High Performance Nonfullerene Polymer Solar Cells with Thick Active Layer over 400 nm

A new n‐type organic semiconductor (n‐OS) acceptor IDTPC with n‐hexyl side chains is developed. Compared to side chains with 4‐hexylphenyl counterparts (IDTCN), such a design endows the acceptor of IDTPC with higher electron mobility, more ordered face‐on molecular packing, and lower band gap. Therefore, the IDTPC‐based polymer solar cells (PSCs) with a newly developed wide bandgap polymer PTQ10 as donor exhibit the maximum power conversion efficiency (PCE) of 12.2%, a near 65% improvement in PCE relative to the IDTCN‐based control device. Most importantly, the IDTPC‐based device is insensitive to the thickness of the active layer from 70 to 505 nm, which still gives a PCE of 10.0% with the active‐layer thickness of 400 nm. To the best of the authors' knowledge, a PCE of 10.0% is the highest value for the nonfullerene PSCs with an active layer thicker than 400 nm. These results reveal that the blend of PTQ10 and IDTPC exhibits great potential for highly efficient nonfullerene PSCs and large‐area device fabrication.     

Improved Tandem All‐Polymer Solar Cells Performance by Using Spectrally Matched Subcells

All‐polymer solar cells (all‐PSCs) are attractive as alternatives to fabricate thermally and mechanically stable solar cells, especially with recent improvements in their power conversion efficiency (PCE). In this work, efficient all‐PSCs with near‐infrared response (up to 850 nm) are developed using newly designed regioregular polymer donors with relatively narrow optical gap. These all‐PSCs systems achieve PCEs up to 6.0% after incorporating fluorine into the polymer backbone. More importantly, these polymers exhibit absorbance that is complementary to previously reported wide bandgap polymer donors. Thus, the superior properties of the newly designed polymers afford opportunities to fabricate the first spectrally matched all‐polymer tandem solar cells with high performance. A PCE of 8.3% is then demonstrated which is the highest efficiency so far for all‐polymer tandem solar cells. The design of narrow bandgap polymers provides new directions to enhance the PCE of emerging single‐junction and tandem all polymer solar cells.     

Thermally Stable All‐Polymer Solar Cells with High Tolerance on Blend Ratios

Tuning the blend composition is an essential step to optimize the power conversion efficiency (PCE) of organic bulk heterojunction (BHJ) solar cells. PCEs from devices of unoptimized donor:acceptor (D:A) weight ratio are generally significantly lower than optimized devices. Here, two high‐performance organic nonfullerene BHJ blends PBDB‐T:ITIC and PBDB‐T:N2200 are adopted to investigate the effect of blend ratio on device performance. It is found that the PCEs of polymer‐polymer (PBDB‐T:N2200) blend are more tolerant to composition changes, relative to polymer‐molecule (PBDB‐T:ITIC) devices. In both systems, short‐circuit current density (J_sc) is tracked closely with PCE, indicating that exciton dissociation and transport strongly influence PCEs. With dilute acceptor concentrations, polymer‐polymer blends maintain high electron mobility relative to the polymer‐molecule blends, which explains the dramatic difference in PCEs between them as a function of D:A blend ratio. In addition, polymer‐polymer solar cells, especially at high D:A blend ratio, are stable (less than 5% relative loss) over 70 d under continuous heating at 80 °C in a glovebox without encapsulation. This work demonstrates that all‐polymer solar cells show advantage in operational lifetime under thermal stress and blend‐ratio resilience, which indicates their high potential for designing of stable and scalable solar cells.     

Room Temperature Processed Highly Efficient Large‐Area Polymer Solar Cells Achieved with Molecular Engineering of Copolymers

The room temperature (RT) processability of the photoactive layers in polymer solar cells (PSCs) from halogen‐free solvent along with their highly reproducible power conversion efficiencies (PCEs) and intrinsic thickness tolerance are extremely desirable for the large‐area roll‐to‐roll (R2R) production. However, most of the photoactive materials in PSCs require elevated processing temperatures due to their strong aggregation, which are unfavorable for the industrial R2R manufacturing of PSCs. These limiting factors for the commercialization of PSCs are alleviated by synthesizing random terpolymers with components of (2‐decyltetradecyl)thiophen‐2‐yl)naphtho[1,2‐c:5,6‐c′]bis[1,2,5]thiadiazole and bithiophene substituted with methyl thiophene‐3‐carboxylate (MTC). In contrast to the temperature‐dependent PNTz4T polymer, the resulting random terpolymers (PNTz4T‐MTC) show better solubility, slightly reduced crystallinity and aggregation, and weaker intermolecular interaction, thus enabling PNTz4T‐MTC to be processed at RT from a halogen‐free solvent. Particularly, the PNTz4T‐5MTC‐based photoactive layer exhibits an excellent PCE of 9.66%, which is among the highest reported PCEs for RT and ecofriendly halogen‐free solvent processed fullerene‐based PSCs, and a thickness tolerance with a PCE exceeding 8% from 100 to 520 nm. Finally, large‐area modules fabricated with the PNTz4T and PNTz4T‐5MTC polymer have shown 4.29% and 6.61% PCE respectively, with an area as high as 54.45 cm² in air.     

Layer‐by‐Layer Solution‐Processed Low‐Bandgap Polymer‐PC61BM Solar Cells with High Efficiency

Polymer solar cells (PSCs) are fabricated without solvent additives using a low‐bandgap polymer, PBDTTT‐C‐T, as the donor and [6,6]‐phenyl‐C61‐butyric‐acid‐methyl‐ester (PC₆₁BM) as the acceptor. Donor‐acceptor blend and layer‐by‐layer (LL) solution process are used to form active layers. Relative to the blend devices, the LL devices exhibit stronger absorption, better vertical phase separation, higher hole and electron mobilities, and better charge extraction at correct electrodes. As a result, after thermal annealing the LL devices exhibit an average power conversion efficiency (PCE) of 6.86%, which is much higher than that of the blend devices (4.31%). The best PCE of the LL devices is 7.13%, which is the highest reported for LL processed PSCs and among the highest reported for PC₆₁BM‐based single‐junction PSCs.     

High‐Performance Thick‐Film All‐Polymer Solar Cells Created Via Ternary Blending of a Novel Wide‐Bandgap Electron‐Donating Copolymer

A novel wide‐bandgap electron‐donating copolymer containing an electron‐deficient, difluorobenzotriazole building block with a siloxane‐terminated side chain is developed. The resulting polymer, poly{(4,8‐bis(4,5‐dihexylthiophen‐2‐yl)benzo[1,2‐b:4,5‐b′]dithiophene‐co‐4,7‐di(thiophen‐2‐yl)‐5,6‐difluoro‐2‐(6‐(1,1,1,3,5,5,5‐heptamethyltri‐siloxan‐3‐yl)hexyl)‐2H‐benzo[d][1,2,3]triazole} (PBTA‐Si), is used to successfully fabricate high‐performance, ternary, all‐polymer solar cells (all‐PSCs) insensitive to the active layer thickness. An impressively high fill factor of ≈76% is achieved with various ternary‐blending ratios. The optimized all‐PSCs attain a power conversion efficiency (PCE) of 9.17% with an active layer thickness of 350 nm and maintain a PCE over 8% for thicknesses over 400 nm, which is the highest reported efficiency for thick all‐PSCs. These results can be attributed to efficient charge transfer, additional energy transfer, high and balanced charge transport, and weak recombination behavior in the photoactive layer. Moreover, the photoactive layers of the ternary all‐PSCs are processed in a nonhalogenated solvent, 2‐methyltetrahydrofuran, which greatly improves their compatibility with large‐scale manufacturing.     

2‐Thiopheneformamidinium‐Based 2D Ruddlesden–Popper Perovskite Solar Cells with Efficiency of 16.72% and Negligible Hysteresis

Formamidinium (FA)‐based 3D perovskite solar cells (PSCs) have been widely studied and they show reduced bandgap, enhanced stability, and improved efficiency compared to MAPbI₃‐based devices. Nevertheless, the FA‐based spacers have rarely been studied for 2D Ruddlesden–Popper (RP) perovskites, which have drawn wide attention due to their enormous potential for fabricating efficient and stable photovoltaic devices. Here, for the first time, FA‐based derivative, 2‐thiopheneformamidinium (ThFA), is successfully synthesized and employed as an organic spacer for 2D RP PSCs. A precursor organic salts‐assisted crystal growth technique is further developed to prepare high quality 2D (ThFA)₂(MA)_n?1Pb_nI_3n+1 (nominal n = 3) perovskite films, which shows preferential vertical growth orientations, high charge carrier mobilities, and reduced trap density. As a result, the 2D RP PSCs with an inverted planar p‐i‐n structure exhibit a dramatically improved power conversion efficiency (PCE) from 7.23% to 16.72% with negligible hysteresis, which is among the highest PCE in 2D RP PSCs with low nominal n‐value of 3. Importantly, the optimized 2D PSCs exhibit a dramatically improved stability with less than 1% degradation after storage in N₂ for 3000 h without encapsulation. These findings provide an effective strategy for developing FA‐based organic spacers toward highly efficient and stable 2D PSCs.     

Bandgap Narrowing in Non‐Fullerene Acceptors: Single Atom Substitution Leads to High Optoelectronic Response Beyond 1000 nm

Two narrow bandgap non‐fullerene acceptors (NBG‐NFAs), namely, COTIC‐4F and SiOTIC‐4F, are designed and synthesized for the fabrication of efficient near‐infrared organic solar cells (OSCs). The chemical structures of the NBG‐NFAs contain a D′‐D‐D′ electron‐rich internal core based on a cyclopentadithiophene (or dithienosilole) (D) and alkoxythienyl (D′) core, end‐capped with the highly electron‐deficient unit 2‐(5,6‐difluoro‐3‐oxo‐2,3‐dihydro‐1H‐inden‐1‐ylidene)malononitrile (A), ultimately providing a A‐D′‐D‐D′‐A molecular configuration that enhances the intramolecular charge transfer characteristics of the excited states. One can thereby reduce the optical bandgap (E_g^opt) to as low as ≈1.10 eV, one of the smallest values for NFAs reported to date. In bulk‐heterojunction (BHJ) OSCs, NBG‐NFA blends with the polymer donor PTB7‐Th yield power conversion efficiencies (PCE) of up to 9.0%, which is particularly high when compared against a range of NBG BHJ blends. Most significantly, it is found that, despite the small energy loss (E_g^opt ? eV_OC) of 0.52 eV, the PTB7‐Th/NBG‐NFA bulk heterojunction blends can yield short‐circuit current densities of up to 22.8 mA cm^?2, suggesting that the design and application of NBG‐NFA materials have substantial potential to further improve the PCE of OSCs.     

Efficiency Enhancement of Polymer Solar Cells Based on Poly(3‐hexylthiophene)/Indene‐C70 Bisadduct via Methylthiophene Additive

Photovoltaic performance of polymer solar cells based on poly(3‐hexylthiophene) (P3HT) as the donor and indene‐C₇₀ bisadduct (IC₇₀BA) as the acceptor is improved by adding 3 vol% 3‐methylthiophene (MT) or 3‐hexylthiophene (HT) as processing additives. The results of UV‐vis absorption spectroscopy, X‐ray diffraction analysis and atomic force microscopy indicate that with the MT or HT processing additive, the active layer of the blend of P3HT/IC₇₀BA showed strengthened absorbance, enhanced crystallinity and improved film morphology. The power conversion efficiency (PCE) of the PSCs was improved from 5.80% for the device without the additive to 6.35% for the device with HT additive and to 6.69% with MT additive. The PCE of 6.69% is the top value reported so far for the PSCs based on P3HT.     

Improve the Performance of the All‐Small‐Molecule Nonfullerene Organic Solar Cells through Enhancing the Crystallinity of Acceptors

Significant development has been achieved in nonfullerene organic solar cells. However, most of the high‐efficiency nonfullerene systems are composed of polymer donors and fused‐ring acceptors, and only a few small molecule donors can work well. Herein, a new A–D–A small molecule donor named NDTSR with naphtho[1,2‐b:5,6‐b′]dithiophene (NDT) as building blocks is synthesized. Two energy levels well‐matched fused‐ring acceptors ITIC and IDIC are chosen to construct all‐small‐molecule solar cells with NDTSR, respectively. When mixed with IDIC, a high power conversion efficiency (PCE) of 8.05% is achieved, which is the highest efficiency for NDT‐based small molecule donor. However, the NDTSR:ITIC system only exhibits a low PCE of 1.77%. The big difference in the performance of these two systems should be attributed to the different morphology and phase separation resulting from the crystallinity and aggregation ability of the acceptors. The results demonstrate that NDT‐based small molecule is a promising candidate donor for all‐small‐molecule systems, while the crystallinity of fused‐ring acceptors is a critical factor for optimizing the phase separation in the active layer.     

Efficient Ternary Polymer Solar Cells with Two Well‐Compatible Donors and One Ultranarrow Bandgap Nonfullerene Acceptor

Nonfullerene polymer solar cells (PSCs) are fabricated by using one wide bandgap donor PBDB‐T and one ultranarrow bandgap acceptor IEICO‐4F as the active layers. One medium bandgap donor PTB7‐Th is selected as the third component due to the similar highest occupied molecular orbital level compared to that of PBDB‐T and their complementary absorption spectra. The champion power conversion efficiency (PCE) of PSCs is increased from 10.25% to 11.62% via incorporating 20 wt% PTB7‐Th in donors, with enhanced short‐circuit current (J_SC) of 24.14 mA cm^?2 and fill factor (FF) of 65.03%. The 11.62% PCE should be the highest value for ternary nonfullerene PSCs. The main contribution of PTB7‐Th can be summarized as the improved photon harvesting and enhanced exciton utilization of PBDB‐T due to the efficient energy transfer from PBDB‐T to PTB7‐Th. Meanwhile, PTB7‐Th can also act as a regulator to adjust PBDB‐T molecular arrangement for optimizing charge transport, resulting in the enhanced FF of ternary PSCs. This experimental result may provide new insight for developing high‐performance ternary nonfullerene PSCs by selecting two well‐compatible donors with different bandgap and one ultranarrow bandgap acceptor.     

A High‐Performance D–A Copolymer Based on Dithieno[3,2‐b:2′,3′‐d]Pyridin‐5(4H)‐One Unit Compatible with Fullerene and Nonfullerene Acceptors in Solar Cells

Development of high‐performance donor–acceptor (D–A) copolymers is vital in the research of polymer solar cells (PSCs). In this work, a low‐bandgap D–A copolymer based on dithieno[3,2‐b:2′,3′‐d]pyridin‐5(4H)‐one unit (DTP), PDTP4TFBT, is developed and used as the donor material for PSCs with PC₇₁BM or ITIC as the acceptor. PDTP4TFBT:PC₇₁BM and PDTP4TFBT:ITIC solar cells give power conversion efficiencies (PCEs) up to 8.75% and 7.58%, respectively. 1,8‐Diiodooctane affects film morphology and device performance for fullerene and nonfullerene solar cells. It inhibits the active materials from forming large domains and improves PCE for PDTP4TFBT:PC₇₁BM cells, while it promotes the aggregation and deteriorates performance for PDTP4TFBT:ITIC cells. The ternary‐blend cells based on PDTP4TFBT:PC₇₁BM:ITIC (1:1.2:0.3) give a decent PCE of 9.20%.     

Achieving Both Enhanced Voltage and Current through Fine‐Tuning Molecular Backbone and Morphology Control in Organic Solar Cells

It is a great challenge to simultaneously improve the two tangled parameters, open circuit voltage (V_oc) and short circuit current density (J_sc) for organic solar cells (OSCs). Herein, such a challenge is addressed by a synergistic approach using fine‐tuning molecular backbone and morphology control simultaneously by a simple yet effective side chain modulation on the backbone of an acceptor–donor–acceptor (A–D–A)‐type acceptor. With this, two terthieno[3,2‐b]thiophene (3TT) based A–D–A‐type acceptors, 3TT‐OCIC with backbone modulation and 3TT‐CIC without such modification, are designed and synthesized. Compared with the controlled molecule 3TT‐CIC, 3TT‐OCIC shows power conversion efficiency (PCE) of 13.13% with improved V_oc of 0.69 V and J_sc of 27.58 mA cm^?2, corresponding to PCE of 12.15% with V_oc of 0.65 V and J_sc of 27.04 mA cm^?2 for 3TT‐CIC–based device. Furthermore, with effective near infrared absorption, 3TT‐OCIC is used as the rear subcell acceptor in a tandem device and gave an excellent PCE of 15.72%.