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.     

Favorable Mixing Thermodynamics in Ternary Polymer Blends for Realizing High Efficiency Plastic Solar Cells

Ternary blends with broad spectral absorption have the potential to increase charge generation in organic solar cells but feature additional complexity due to limited intermixing and electronic mismatch. Here, a model system comprising the polymers poly[5,5‐bis(2‐butyloctyl)‐(2,2‐bithiophene)‐4,4‐dicarboxylate‐alt‐5,5‐2,2‐bithiophene] (PDCBT) and PTB7‐Th and PC₇₀BM as an electron accepting unit is presented. The power conversion efficiency (PCE) of the ternary system clearly surpasses the performance of either of the binary systems. The photophysics is governed by a fast energy transfer process from PDCBT to PTB7‐Th, followed by electron transfer at the PTB7‐Th:fullerene interface. The morphological motif in the ternary blend is characterized by polymer fibers. Based on a combination of photophysical analysis, GIWAXS measurements and calculation of the intermolecular parameter, the latter indicating a very favorable molecular affinity between PDCBT and PTB7‐Th, it is proposed that an efficient charge generation mechanism is possible because PTB7‐Th predominantly orients around PDCBT filaments, allowing energy to be effectively relayed from PDCBT to PTB7‐Th. Fullerene can be replaced by a nonfullerene acceptor without sacrifices in charge generation, achieving a PCE above 11%. These results support the idea that thermodynamic mixing and energetics of the polymer–polymer interface are critical design parameter for realizing highly efficient ternary solar cells with variable electron acceptors.     

Rational Strategy to Stabilize an Unstable High‐Efficiency Binary Nonfullerene Organic Solar Cells with a Third Component

Long device lifetime is still a missing key requirement in the commercialization of nonfullerene acceptor (NFA) organic solar cell technology. Understanding thermodynamic factors driving morphology degradation or stabilization is correspondingly lacking. In this report, thermodynamics is combined with morphology to elucidate the instability of highly efficient PTB7‐Th:IEICO‐4F binary solar cells and to rationally use PC₇₁BM in ternary solar cells to reduce the loss in the power conversion efficiency from ≈35% to <10% after storage for 90 days and at the same time improve performance. The hypomiscibility observed for IEICO‐4F in PTB7‐Th (below the percolation threshold) leads to overpurification of the mixed domains. By contrast, the hypermiscibility of PC₇₁BM in PTB7‐Th of 48 vol% is well above the percolation threshold. At the same time, PC₇₁BM is partly miscible in IEICO‐4F suppressing crystallization of IEICO‐4F. This work systematically illustrates the origin of the intrinsic degradation of PTB7‐Th:IEICO‐4F binary solar cells, demonstrates the structure–function relations among thermodynamics, morphology, and photovoltaic performance, and finally carries out a rational strategy to suppress the degradation: the third component needs to have a miscibility in the donor polymer at or above the percolation threshold, yet also needs to be partly miscible with the crystallizable acceptor.     

Ternary Organic Solar Cells with Minimum Voltage Losses

A new strategy for designing ternary solar cells is reported in this paper. A low‐bandgap polymer named PTB7‐Th and a high‐bandgap polymer named PBDTTS‐FTAZ sharing the same bulk ionization potential and interface positive integer charge transfer energy while featuring complementary absorption spectra are selected. They are used to fabricate efficient ternary solar cells, where the hole can be transported freely between the two donor polymers and collected by the electrode as in one broadband low bandgap polymer. Furthermore, the fullerene acceptor is chosen so that the energy of the positive integer charge transfer state of the two donor polymers is equal to the energy of negative integer charge transfer state of the fullerene, enabling enhanced dissociation of all polymer donor and fullerene acceptor excitons and suppressed bimolecular and trap assistant recombination. The two donor polymers feature good miscibility and energy transfer from high‐bandgap polymer of PBDTTS‐FTAZ to low‐bandgap polymer of PTB7‐Th, which contribute to enhanced performance of the ternary solar cell.     

Intra‐Molecular Donor–Acceptor Interaction Effects on Charge Dissociation,Charge Transport,and Charge Collection in Bulk‐Heterojunction Organic Solar Cells

This article reports experimental studies on internal charge dissociation, transport, and collection by using magnetic field effects of photocurrent (MFE_PC) and light‐assisted dielectric response (LADR) in highly‐efficient organic solar cells based on photovoltaic polymer PTB2 and PTB4 with intra‐molecular “donor–acceptor” interaction. The MFE_PC at low‐field (< 150 mT) indicates that intra‐molecular “donor‐acceptor” interaction generates charge dissociation in un‐doped PTB2 and PTB4 films, which is similar to that in lightly doped P3HT (Poly(3‐hexylthiophene)) with 5 wt% PCBM (1‐(3‐methyloxycarbonyl)‐propyl‐1‐phenyl (6,6) C₆₁). After PTB2 and PTB4 are mixed with PCBM to form bulk‐heterojunctions, the MFE_PC at high‐field (> 150 mT) reveals that the charge‐transfer complexes formed at PTB2:PCBM and PTB4:PCBM interfaces have much lower binding energies due to stronger electron‐withdrawing abilities, as compared to the P3HT:PCBM device, towards the generation of photocurrent. Furthermore, the light‐assisted dielectric response: LADR indicates that the PTB2:PCBM and PTB4:PCBM solar cells exhibit larger capacitances relative to P3HT:PCBM device under photoexcitation. This reflects that the PTB2:PCBM and PTB4:PCBM bulk heterojunctions have more effective charge transport and collection than the P3HT:PCBM counterpart. As a result, our experimental results indicate that intra‐molecular “donor‐acceptor” interaction plays an important role to enhance charge dissociation, transport, and collection in bulk‐heterojunction organic solar cells.     

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.     

Recombination Losses Above and Below the Transport Percolation Threshold in Bulk Heterojunction Organic Solar Cells

Achieving the highest power conversion efficiencies in bulk heterojunction organic solar cells requires a morphology that delivers electron and hole percolation pathways for optimized transport, plus sufficient donor:acceptor contact area for near unity charge transfer state formation. This is a significant structural challenge, particularly in semiconducting polymer:fullerene systems. This balancing act in the model high efficiency PTB7:PC70BM blend is studied by tuning the donor:acceptor ratio, with a view to understanding the recombination loss mechanisms above and below the fullerene transport percolation threshold. The internal quantum efficiency is found to be strongly correlated to the slower carrier mobility in agreement with other recent studies. Furthermore, second‐order recombination losses dominate the shape of the current density–voltage curve in efficient blend combinations, where the fullerene phase is percolated. However, below the charge transport percolation threshold, there is an electric‐field dependence of first‐order losses, which includes electric‐field‐dependent photogeneration. In the intermediate regime, the fill factor appears to be limited by both first‐ and second‐order losses. These findings provide additional basic understanding of the interplay between the bulk heterojunction morphology and the order of recombination in organic solar cells. They also shed light on the limitations of widely used transport models below the percolation threshold.     

Bis(Naphthalene Imide)diphenylanthrazolines: A New Class of Electron Acceptors for Efficient Nonfullerene Organic Solar Cells and Applicable to Multiple Donor Polymers

Unlike universally applicable fullerene derivatives, current nonfullerene electron acceptors are rarely effective with more than one donor polymer in bulk heterojunction (BHJ) solar cells. A novel class of nonfullerene electron acceptors, bis(naphthalene imide)‐3,6‐diphenyl‐trans‐anthrazolines (BNIDPAs), that is applicable and yields efficient photovoltaic devices with multiple donor polymers, including a thiazolothiazole–dithienosilole copolymer (PSEHTT) and benzodithiophene copolymers (PBDTT‐FTTE and PTB7) is reported. Photovoltaic devices composed of the BNIDPA‐butyloctyl (BO) acceptor with PSEHTT, PBDTT‐FTTE, and PTB7, respectively, have power conversion efficiencies of 3.0%–3.1% with high open‐circuit voltages of ≈1.0 V. In contrast, BHJ devices composed of BNIDPA‐DT acceptor with larger 2‐decyltetradecyl chains and the same donor polymers have substantially reduced bulk electron mobility and reduced photovoltaic efficiencies of 1.3%–1.7%, which highlight the critical role of the size of alkyl chains appended onto nonfullerene electron acceptors. The present results provide a rare example of nonfullerene electron acceptors that are capable of pairing with multiple donor polymers to achieve efficient BHJ solar cells.     

π‐Extended Narrow‐Bandgap Diketopyrrolopyrrole‐Based Oligomers for Solution‐Processed Inverted Organic Solar Cells

A series of narrow‐bandgap π‐conjugated oligomers based on diketopyrrolopyrrole chromophoric units coupled with benzodithiophene, indacenodithiophene, thiophene, and isoindigo cores are designed and synthesized for application as donor materials in solution‐processed small‐molecule organic solar cells. The impacts of these different central cores on the optoelectronic and morphological properties, carrier mobility, and photovoltaic performance are investigated. These π‐extended oligomers possess broad and intense optical absorption covering the range from 550 to 750 nm, narrow optical bandgaps of 1.52–1.69 eV, and relatively low‐lying highest occupied molecular orbital (HOMO) energy levels ranging from ?5.24 to ?5.46 eV in their thin films. A high power conversion efficiency of 5.9% under simulated AM 1.5G illumination is achieved for inverted organic solar cells based on a small‐molecule bulk‐heterojunction system consisting of a benzodithiophene‐diketopyrrolopyrrole‐containing oligomer as a donor and [6,6]‐phenyl‐C₇₁‐butyric acid methyl ester (PC₇₁BM) as an acceptor. Transmission electron microscopy and energy‐dispersive X‐ray spectroscopy reveal that interpenetrating and interconnected donor/acceptor domains with pronounced mesoscopic phase segregation are formed within the photoactive binary blends, which is ideal for efficient exciton dissociation and charge transport in the bulk‐heterojunction devices.     

A Halogenation Strategy for over 12% Efficiency Nonfullerene Organic Solar Cells

Three acceptor–donor–acceptor type nonfullerene acceptors (NFAs), namely, F–F, F–Cl, and F–Br, are designed and synthesized through a halogenation strategy on one successful nonfullerene acceptor FDICTF (F–H). The three molecules show red‐shifted absorptions, increased crystallinities, and higher charge mobilities compared with the F–H. After blending with donor polymer PBDB‐T, the F–F‐, F–Cl‐, and F–Br‐based devices exhibit power conversion efficiencies (PCEs) of 10.85%, 11.47%, and 12.05%, respectively, which are higher than that of F–H with PCE of 9.59%. These results indicate that manipulating the absorption range, crystallinity and mobilities of NFAs by introducing different halogen atoms is an effective way to achieve high photovoltaic performance, which will offer valuable insight for the designing of high‐efficiency organic solar cells.     

Terthieno[3,2‐b]Thiophene (6T) Based Low Bandgap Fused‐Ring Electron Acceptor for Highly Efficient Solar Cells with a High Short‐Circuit Current Density and Low Open‐Circuit Voltage Loss

A terthieno[3,2‐b]thiophene ( 6T ) based fused‐ring low bandgap electron acceptor, 6TIC , is designed and synthesized for highly efficient nonfullerene solar cells. The chemical, optical, and physical properties, device characteristics, and film morphology of 6TIC are intensively studied. 6TIC shows a narrow bandgap with band edge reaching 905 nm due to the electron‐rich π‐conjugated 6T core and reduced resonance stabilization energy. The rigid, π‐conjugated 6T also offers lower reorganization energy to facilitate very low V_OC loss in the 6TIC system. The analysis of film morphology shows that PTB7‐Th and 6TIC can form crystalline domains and a bicontinuous network. These domains are enlarged when thermal annealing is applied. Consequently, the device based on PTB7‐Th : 6TIC exhibits a high power conversion efficiency (PCE) of 11.07% with a high J_SC > 20 mA cm^?2 and a high V_OC of 0.83 V with a relatively low V_OC loss (≈0.55 V). Moreover, a semitransparent solar cell based on PTB7‐Th : 6TIC exhibits a relatively high PCE (7.62%). The device can have combined high PCE and high J_SC is quite rare for organic solar cells.     

Toward High‐Temperature Stability of PTB7‐Based Bulk Heterojunction Solar Cells: Impact of Fullerene Size and Solvent Additive

The use of fullerene as acceptor limits the thermal stability of organic solar cells at high temperatures as their diffusion inside the donor leads to phase separation via Ostwald ripening. Here it is reported that fullerene diffusion is fully suppressed at temperatures up to 140 °C in bulk heterojunctions based on the benzodithiophene‐based polymer (the poly[[4,8‐bis[(2‐ethylhexyl)oxy]‐benzo[1,2‐b:4,5‐b′]dithiophene‐2,6‐diyl][3‐fluoro‐2‐[(2‐ethylhexyl)carbonyl]‐thieno[3,4‐b]thiophenediyl]], (PTB7) in combination with the fullerene derivative [6,6]‐phenyl‐C71‐butyric acid methyl ester (PC₇₀BM). The blend stability is found independently of the presence of diiodooctane (DIO) used to optimize nanostructuration and in contrast to PTB7 blends using the smaller fullerene derivative PC₇₀BM. The unprecedented thermal stability of PTB7:PC₇₀BM layers is addressed to local minima in the mixing enthalpy of the blend forming stable phases that inhibit fullerene diffusion. Importantly, although the nanoscale morphology of DIO processed blends is thermally stable, corresponding devices show strong performance losses under thermal stress. Only by the use of a high temperature annealing step removing residual DIO from the device, remarkably stable high efficiency solar cells with performance losses less than 10% after a continuous annealing at 140 °C over 3 days are obtained. These results pave the way toward high temperature stable polymer solar cells using fullerene acceptors.     

Suppressing Energy Loss due to Triplet Exciton Formation in Organic Solar Cells: The Role of Chemical Structures and Molecular Packing

In the most efficient solar cells based on blends of a conjugated polymer (electron donor) and a fullerene derivative (electron acceptor),ultrafast formation of charge‐transfer (CT) electronic states at the donor‐acceptor interfaces and efficient separation of these CT states into free charges, lead to internal quantum efficiencies near 100%. However, there occur substantial energy losses due to the non‐radiative recombinations of the charges, mediated by the loweset‐energy (singlet and triplet) CT states; for example, such recombinations can lead to the formation of triplet excited electronic states on the polymer chains, which do not generate free charges. This issue remains a major factor limiting the power conversion efficiencies (PCE) of these devices. The recombination rates are, however, difficult to quantify experimentally. To shed light on these issues, here, an integrated multi‐scale theoretical approach that combines molecular dynamics simulations with quantum chemistry calculations is employed in order to establish the relationships among chemical structures, molecular packing, and non‐radiative recombination losses mediated by the lowest‐energy charge‐transfer states.     

15% Efficiency Tandem Organic Solar Cell Based on a Novel Highly Efficient Wide‐Bandgap Nonfullerene Acceptor with Low Energy Loss

A tandem organic solar cell (OSC) is a valid structure to widen the photon response range and suppress the transmission loss and thermalization loss. In the past few years, the development of low‐bandgap materials with broad absorption in long‐wavelength region for back subcells has attracted considerable attention. However, wide‐bandgap materials for front cells that have both high short‐circuit current density (J_SC) and open‐circuit voltage (V_OC) are scarce. In this work, a new fluorine‐substituted wide‐bandgap small molecule nonfullerene acceptor TfIF‐4FIC is reported, which has an optical bandgap of 1.61 eV. When PBDB‐T‐2F is selected as the donor, the device offers an extremely high V_OC of 0.98 V, a high J_SC of 17.6 mA cm^?2, and a power conversion efficiency of 13.1%. This is the best performing acceptor with such a wide bandgap. More importantly, the energy loss in this combination is 0.63 eV. These properties ensure that PBDB‐T‐2F:TfIF‐4FIC is an ideal candidate for the fabrication of tandem OSCs. When PBDB‐T‐2F:TfIF‐4FIC and PTB7‐Th:PCDTBT:IEICO‐4F are used as the front cell and the back cell to construct tandem solar cells, a PCE of 15% is obtained, which is one of best results reported to date in the field of organic solar cells.     

The Crucial Influence of Fullerene Phases on Photogeneration in Organic Bulk Heterojunction Solar Cells

The conjugated polymer, poly(2,5‐bis(3‐hexadecylthiophen‐2‐yl)thieno[3,2‐b]thiophene) (pBTTT‐C₁₆), allows a systematic tuning of the blend morphology by varying the acceptor type and fraction, making it a well‐suited structural model for studying the fundamental processes in organic bulk heterojunction solar cells. To analyze the role of intercalated and pure fullerene domains on charge carrier photogeneration, time delayed collection field (TDCF) measurements and Fourier‐transform photocurrent spectroscopy (FTPS) are performed on pBTTT‐C₁₆:[6,6]‐phenyl‐C₆₁‐butyric acid methyl ester (PC₆₁BM) solar cells with various stoichiometries. A weak influence of excess photon energy on photogeneration along with a photogeneration having a weaker field dependence at increasing fullerene loading is found. The findings are assigned to a dissociation via thermalized charge transfer (CT) states supported by an enhanced electron delocalization along spatially extended PC₆₁BM nanophases that form in addition to a bimolecular crystal (BMC) for PC₆₁BM rich blends. The highly efficient transfer of charge carriers from the BMC into the pure domains are studied further by TDCF measurements performed on non‐intercalated pBTTT‐C₁₆:bisPC₆₁BM blends. They reveal a field dependent charge generation similar to the 1:4 PC₆₁BM blend, demonstrating that the presence of pure acceptor phases is the major driving force for an efficient, field independent CT dissociation.     

High‐Performance Tandem Organic Solar Cells Using HSolar as the Interconnecting Layer

Tandem structure provides a practical way to realize high efficiency organic photovoltaic cells, it can be used to extend the wavelength coverage for light harvesting. The interconnecting layer (ICL) between subcells plays a critical role in the reproducibility and performance of tandem solar cells, yet the processability of the ICL has been a challenge. In this work the fabrication of highly reproducible and efficient tandem solar cells by employing a commercially available material, PEDOT:PSS HTL Solar (HSolar), as the hole transporting material used for the ICL is reported. Comparing with the conventional PEDOT:PSS Al 4083 (c‐PEDOT), HSolar offers a better wettability on the underlying nonfullerene photoactive layers, resulting in better charge extraction properties of the ICL. When FTAZ:IT‐M and PTB7‐Th:IEICO‐4F are used as the subcells, a power conversion efficiency (PCE) of 14.7% is achieved in the tandem solar cell. To validate the processability of these tandem solar cells, three other research groups have successfully fabricated tandem devices using the same recipe and the highest PCE obtained is 16.1%. With further development of donor polymers and device optimization, the device simulation results show that a PCE > 22% can be realized in tandem cells in the near future.     

Unifying Charge Generation,Recombination, and Extraction in Low‐Offset Non‐Fullerene Acceptor Organic Solar Cells

Even though significant breakthroughs with over 18% power conversion efficiencies (PCEs) in polymer:non‐fullerene acceptor (NFA) bulk heterojunction organic solar cells (OSCs) have been achieved, not many studies have focused on acquiring a comprehensive understanding of the underlying mechanisms governing these systems. This is because it can be challenging to delineate device photophysics in polymer:NFA blends comprehensively, and even more complicated to trace the origins of the differences in device photophysics to the subtle differences in energetics and morphology. Here, a systematic study of a series of polymer:NFA blends is conducted to unify and correlate the cumulative effects of i) voltage losses, ii) charge generation efficiencies, iii) non‐geminate recombination and extraction dynamics, and iv) nuanced morphological differences with device performances. Most importantly, a deconvolution of the major loss processes in polymer:NFA blends and their connections to the complex BHJ morphology and energetics are established. An extension to advanced morphological techniques, such as solid‐state NMR (for atomic level insights on the local ordering and donor:acceptor π? π interactions) and resonant soft X‐ray scattering (for donor and acceptor interfacial area and domain spacings), provide detailed insights on how efficient charge generation, transport, and extraction processes can outweigh increased voltage losses to yield high PCEs.     

Mapping Nonfullerene Acceptors with a Novel Wide Bandgap Polymer for High Performance Polymer Solar Cells

A new weak electron‐deficient building block, bis(2‐ethylhexyl) 2,5‐bis(5‐bromothiophen‐2‐yl) thieno[3,2‐b]thiophene‐3,6‐dicarboxylate ( TT‐Th ), is incorporated to construct a wide‐bandgap (1.88 eV) polymer PBDT‐TT for nonfullerene polymer solar cells (NF‐PSCs). PBDT‐TT possesses suitable energy levels and complementary absorption when blended with both ITIC analogues ( ITIC and IT‐M ) and a near‐infrared (NIR) acceptor ( 6TIC ). Moreover, PBDT‐TT exhibits good conjugated planarity and preferable face‐on orientation in the blended thin film, which are beneficial for charge transfer and carrier transport. The PSCs based on PBDT‐TT : IT‐M and PBDT‐TT : 6TIC blend films yield high power conversion efficiencies of 11.38% and 11.03%, respectively. To the best of the authors' knowledge, the PCE of 11.03% for PBDT‐TT : 6TIC‐ based device is one of the highest values reported for NIR NF‐PSCs. This work demonstrates that TT‐Th is a useful new electron‐accepting building block for making p‐type wide bandgap polymers for efficient NIR NF‐PSCs.     

Combining Energy Transfer and Optimized Morphology for Highly Efficient Ternary Polymer Solar Cells

Aimed at achieving ideal morphology, illuminating morphology–performance relationship, and further improving the power conversion efficiency (PCE) of ternary polymer solar cells (TSCs), a ternary system is designed based on PTB7‐Th:PffBT4T‐2OD:PC₇₁BM in this work. The PffBT4T‐2OD owns large absorption cross section, proper energy levels, and good crystallinity, which enhances exciton generation, charge dissociation and transport and suppresses charge recombination, thus remarkably increasing the short‐circuit current density (J _sc) and fill factor (FF). Finally, a notable PCE of 10.72% is obtained for the TSCs with 15% weight ratio of PffBT4T‐2OD. As for the working mechanism, it confirmed the energy transfer from PffBT4T‐2OD to PTB7‐Th, which contributes to the improved exciton generation. And morphology characterization indicates that the devices with 15% PffBT4T‐2OD possess both appropriate domain size (25 nm) and enhanced domain purity. Under this condition, it affords numerous D/A interface for exciton dissociation and good bicontinuous nanostructure for charge transport simultaneously. As a result, the device with 15% PffBT4T‐2OD exhibits improved exciton generation, enhanced charge dissociation possibility, elevated hole mobility and inhibited charge recombination, leading to elevated J _sc (19.02 mA cm^?2) and FF (72.62%) simultaneously. This work indicates that morphology optimization as well as energy transfer plays a significant role in improving TSC performance.