Medium Bandgap Polymer Research Articles

Precisely Controlling Polymer Acceptors with Weak Intramolecular Charge Transfer Effect and Superior Coplanarity for Efficient Indoor All-Polymer Solar Cells with over 27% Efficiency.

Indoor photovoltaics (IPVs) are garnering increasing attention from both the academic and industrial communities due to the pressing demand of the ecosystem of Internet-of-Things. All-polymer solar cells (all-PSCs), emerging as a sub-type of organic photovoltaics, with the merits of great film-forming properties, remarkable morphological and light stability, hold great promise to simultaneously achieve high efficiency and long-term operation in IPV's application. However, the dearth of polymer acceptors with medium-bandgap has impeded the rapid development of indoor all-PSCs. Herein, a highly efficient medium-bandgap polymer acceptor (PYFO-V) is reported through the synergistic effects of side chain engineering and linkage modulation and applied for indoor all-PSCs operation. As a result, the PM6:PYFO-V-based indoor all-PSC yields the highest efficiency of 27.1% under LED light condition, marking the highest value for reported binary indoor all-PSCs to date. More importantly, the blade-coated devices using non-halogenated solvent (o-xylene) maintain an efficiency of over 23%, demonstrating the potential for industry-scale fabrication. This work not only highlights the importance of fine-tuning intramolecular charge transfer effect and intrachain coplanarity in developing high-performance medium-bandgap polymer acceptors but also provides a highly efficient strategy for indoor all-PSC application.

Organic X‐Ray Image Sensors Using a Medium Bandgap Polymer Donor with Low Dark Current

The development of portable X‐ray detectors is necessary for diagnosing fractures in unconscious patients in emergency situations. However, this is quite challenging because of the heavy weight of the scintillator and silicon photodetectors. The weight and thickness of X‐ray detectors can be reduced by replacing the silicon layer with an organic photodetectors. This study presents a novel bithienopyrroledione‐based polymer donor that exhibits excellent photodetection properties even in a thick photoactive layer (~700 nm), owing to the symmetric backbone and highly soluble molecular structure of bithienopyrroledione. The ability of bithienopyrroledione‐based polymer donor to strongly suppress the dark current density (Jd ~ 10−10 A cm−2) at a negative bias (−2.0 V) while maintaining high responsivity (R = 0.29 A W−1) even at a thickness of 700 nm results in a maximum shot‐noise‐limited specific detectivity of Dsh* = 2.18 × 1013 Jones in the organic photodetectors. Printed organic photodetectors are developed by slot‐die coating for use in X‐ray detectors, which exhibit Dsh* = 2.73 × 1012 Jones with clear rising (0.26 s) and falling (0.29 s) response times upon X‐ray irradiation. Detection reliability is also proven by linear response of the X‐ray detector, and the X‐ray detection limit is 3 mA.

High-performance nonfullerene polymer solar cells based on chlorinated quinoxaline copolymer with a high short-circuit current density

In organic solar cells, the absorption range and extinction coefficient of the active layer not only affect the charge separation and carrier transfer efficiency of excitons, but also influence the JSC, and thus the device efficiency. Herein, an efficient nonfullerene polymer solar cells (NF–PSCs) based on a medium-bandgap (MBG) polymer donor PBDTTS-TClQx comprising chlorinethiophene quinoxaline (Qx) unit and a small molecule nonfullerene acceptor (SM-NFA) Y6 is developed. The PBDTTS-TClQx shows a strong absorption in the wavelength region of 330∼750 nm with an optical band gaps (Egopt) of 1.68 eV, which is well complementary with that of Y6 (1.33 eV) and facilitates achieving of high short-circuit current (JSC) in PSCs. As a result, the PBDTTS-TClQx:Y6-based PSCs achieved a power conversion efficiency (PCE) of 14.28% with a JSC of 25.9 mA cm−2. The JSC of 25.9 mA cm−2 achieved is among the highest reported for Qx-based polymer donors in PSCs.

Efficient dialkyl‐difluoro‐substituted quinoxaline‐based medium bandgap polymeric donor for high‐energy‐converting organic solar cells

AbstractA new medium bandgap polymer incorporating electron‐rich 4,8‐bis(5‐(2‐ethylhexyl)thiophen‐2‐yl)benzo[1,2‐b:4,5‐b']dithiophene (BDTT) and electron‐deficient 2,3‐didodecyl‐6,7‐difluoro‐5,8‐di(thiophen‐2‐yl)quinoxaline (2TffQ) units in an alternate manner, namely P(BDTT‐2TffQ), was prepared for organic solar cell (OSC) applications. The optical and electrochemical properties of P(BDTT‐2TffQ) were found to be suitable to use it as an electron donor in OSCs. The absorption band covers the region from 300 to 600 nm with an optical bandgap (Eg) of 1.84 eV, and it highest occupied and lowest unoccupied molecular orbitals (HOMO and LUMO) were found to be positioned at −5.36 and − 3.52 eV. The OSCs prepared by using P(BDTT‐2TffQ):[6,6]‐Phenyl‐C71‐butyric acid methyl ester (PC70BM) and P(BDTT‐2TffQ):2,2′‐((2Z,2'Z)‐((12,13‐bis(2‐ethylhexyl)‐3,9‐diundecyl‐12,13‐dihydro‐[1,2,5]thiadiazolo[3,4‐e]thieno[2″,3″:4′,5′]thieno[2′,3′:4,5]pyrrolo[3,2‐g]thieno[2′,3′:4,5]thieno[3,2‐b]indole‐2,10‐diyl)bis(methanylylidene))bis(5,6‐difluoro‐3‐oxo‐2,3‐dihydro‐1H‐indene‐2,1‐diylidene))dimalononitrile (Y6) blends provided a maximum power conversion efficiency (PCE) of 5.50% and 11.65%, respectively. The differences in the photovoltaic performances of OSCs are mainly attributed to their dissimilar short‐circuit current (Jsc), which depends on their absorption spectrum. Herein, we also compared the properties of P(BDTT‐2TffQ) with a structurally similar polymer, namely P(BDTT‐2TfQ), made up of BDTT and 2,3‐didodecyl‐6‐fluoro‐5,8‐di(thiophen‐2‐yl)quinoxaline (2TfQ) units, for better understanding the effects of the incorporation of additional fluorine atom on the backbone of quinoxaline‐based polymers.

Enhanced Efficiency and Stability of Novel Pseudo-ternary Polymer Solar Cells Enabled by a Conjugated Donor Block Copolymer.

The recent breakthrough in power conversion efficiencies (PCEs) of polymer solar cells (PSCs) that contain an active layer of a ternary system has achieved values of 18-19%; this has sparked interest for further research. However, this system has difficulties in optimizing the composition and controlling the interaction between the three active materials. In this study, we investigated the use of a donor1 (D1)-donor2 (D2) conjugated block copolymer (CBP), PM6-b-TT, to replace the physical blend of two donors. PM6-b-TT, which exhibits an extended absorption range, was synthesized by covalently bonding PM6, a medium-band gap polymer, with PBDT-TT, a wide-band gap polymer. The blend films containing PM6-b-TT and Y6-BO acceptor, demonstrated excellent crystallinity and a film morphology favorable for PSCs. The corresponding pseudo-ternary PSC exhibited significantly higher PCE and thermal stability than the PM6:PBDT-TT-based ternary device. This study unambiguously demonstrates that the novel D1-D2 CBP strategy, combined with the conventional binary and ternary system advantages, is a promising material production strategy that can boost the performance of future PSCs.

Direct arylation polycondensation for the synthesis of medium-bandgap polymer donors (PBDB-T) for organic photovoltaics

Direct arylation polycondensation for the synthesis of medium-bandgap polymer donors (PBDB-T) for organic photovoltaics

Near-Infrared All-Fused-Ring Nonfullerene Acceptors Achieving an Optimal Efficiency-Cost-Stability Balance in Organic Solar Cells

Near-Infrared All-Fused-Ring Nonfullerene Acceptors Achieving an Optimal Efficiency-Cost-Stability Balance in Organic Solar Cells

Performances of two side-chain modified medium-bandgap alternating polymers with main-chain twisted non-fullerene acceptor

Two alternating polymers (P3 and P4) based on side-chain modified benzo[1,2-b:4,5-b′]dithiophene as the electron-donating unit and fluorinated benzothiadiazole derivatives as the electron-withdrawing segment were adopted as donor materials to blend with a main-chain twisted non-fullerene acceptor (i-IEICO-4 F) for bulk heterojunction polymer solar cells (PSCs). The effects of the two types of side-chain substitutions on the UV-Vis absorptive characteristics, frontier molecular orbitals, and photovoltaic performances of the polymers were systematically probed. Both two polymers have medium-bandgaps, 1.75 eV for P3 and 1.71 eV for P4, respectively, guaranteeing the complementary absorption with i-IEICO-4 F. Among these polymers, the device of polymer P3, which has 2,3-octylthienyl side-chain, shows enhanced dielectric constant, suppressed trap-assisted recombination, promoted hole mobility with more balanced carrier mobility, and suitable phase separation, thus successfully achieving an efficiency of 10.67%. While the alkoxylphenyl substituted polymer P4 has slightly deepened molecular energy level and bathochromic-shifted absorption spectrum and achieved enhanced open-circuit voltage, improved electron mobility, and inhibitive bimolecular recombination in the device, thus acquiring a slightly reduced efficiency of 10.19%. This work not only elaborates the applicability of benzothiadiazole-based medium bandgap polymer donors with main-chain twisted acceptors but also reveals the importance of the side-chain modification of the polymer donors on the performances of the fabricated PSCs.

Efficient Organic Solar Cells Enabled by Chlorinated Nonplanar Small Molecules

Recently, the modification of end-capping groups for non-fullerene small molecules has been shown to be attractive as a promising structural-design strategy to construct effective electron acceptors for organic solar cells (OSCs) due to the tailorable molecular energy levels, tunable molar extinction coefficients, and easy-adjusting phase separation characteristic of the resultant acceptors. The application of chlorine substituents onto the ending groups of non-fullerene acceptors (NFAs) has positive effects such as an enhanced intermolecular charge-transfer effect between the electron-donating and electron-withdrawing structures, thus leading to broadening of the absorption regions. Lately, a series of NFAs containing appropriate nonplanar main chains have achieved promising performances. To further investigate the main-chain twisted NFAs, two chlorinated nonplanar small molecules were designed and prepared. Compared to the mono-chlorinated analogue (i-IEICO-2Cl), the dichlorinated molecule (i-IEICO-4Cl) had a bathochromic-shifted absorption spectrum with enhanced absorption intensity and a deeper molecular energy level. Blending with a medium band gap polymer donor (J52), the device of i-IEICO-4Cl shows more balanced charge mobilities and inhibitory charge recombinations, yielding a high efficiency of 12.16%, which is superior to 11.45% of an i-IEICO-2Cl-based OSC, revealing the effectiveness of chlorinated main-chain twisted acceptors for OSCs.

PCDTBT8‐Doped PffBT4T‐2OD‐Based Ternary Solar Cells with Enhanced Open‐Circuit Voltage, Fill Factor, and Charge Separation Efficiency

The effect of a medium bandgap polymer doped into conventional binary heterojunction solar cells is investigated for ternary solar cells, which display different characteristics compared with traditional materials. First, the charge separation and recombination at the multi‐interface (double donors/single acceptor) and the charge transport between different phases are simulated to reveal the competition mechanism of electron transfer and insights into the merits and demerits of a hole transport layer with medium and narrow band gaps. Second, global modeling of performance for PCDTBT8‐doped PffBT4T‐2OD‐based ternary solar cells is established to evaluate the crucial parameters (open‐circuit voltage (V OC), short‐circuit current (J SC), fill factor (FF), and power conversion efficiency (PCE)) related to the experiment. The results demonstrate that the orbital energy levels, absorption peak, excited‐state, fluorescence lifetimes, and hole transportability are tunable upon the medium bandgap polymer doping process. The electron transfer process for the multi‐interface is enhanced by doping different bandgap polymers compared with a single interface, which contributes to the energy match and multistep jump mechanism. Ternary solar cells based on the doped polymer exhibit better V OC, FF, and PCE with weakened J SC. The theoretical calculations are in excellent agreement with experimental results. The global investigation of ternary solar cells can be used to interpret experiments and is viewed as an effective method for screening high‐performance solar cells.

Effect of extending fluorinated thiophene π-bridges of BDT- and TT-based polymers for nonfullerene organic solar cells

A series of novel benzo[1,2-b:4,5-b]dithiophene (BDT) and thieno[3,4-b]thiophene (TT)-based medium-bandgap polymers (PBDTTT-2F and PBDTTT-3F) were synthesized using a Stille cross-coupling reaction; these polymers contain fluorinated thiophene π-bridges. The number-average molecular weights (Mn) of PBDTTT-2F and PBDTTT-3F are 37 kDa and 21 kDa, with dispersities of 2.5 and 2.7, respectively. The bandgap energies of PBDTTT-2F and PBDTTT-3F are 1.75 eV and 1.76 eV, respectively. The absorption regions of PBDTTT-2F and PBDTTT-3F cover 300–700 nm, which is complementary to the absorption range of the nonfullerene acceptor (IT-4F). The polymers were combined with IT-4F to fabricate bulk heterojunction solar cells. The PBDTTT-2F:IT-4F and PBDTTT-3F:IT-4F organic solar cells exhibited power conversion efficiencies (PCEs) of 9.52% and 9.08%, with short-circuit current densities of 17.13 and 16.58 mA cm−2, open-circuit voltages of 0.78 and 0.81 V, and fill factors of 72% and 68%, respectively. The superior PCE of the PBDTTT-2F:IT-4F device compared with that of the PBDTTT-3F:IT-4F device is attributed to the enhanced exciton dissociation, reduced charge recombination, and high carrier mobility in the PBDTTT-2F:IT-4F device.

Fused perylenediimide dimer as nonfullerene acceptor for high-performance organic solar cells

Four perylenediimide (PDI) dimers UFPDI, FPDI, UFPDI-T and FPDI-T are synthesized and used as nonfullerene acceptors for the fabrication of organic solar cells with the medium-bandgap polymer PBDB-T as the donor material. These four acceptors with three-dimensional molecular structures display good solubilities in the processing solvent, which is helpful to form nanoscale separation when blended with the polymer donor. The PDI subunits in the unfused PDI dimers UFPDI and UFPDI-T are twisted and the two acceptors display a broad featureless absorption in the visible region. The fused PDI dimers FPDI and FPDI-T display an X-shaped geometry with large dihedral angles of approximately 40° and their PDI subunits are planar. The fused PDI dimers with the X-shaped molecular conformation is helpful for suppressing the formation of large sized aggregations and the planar PDI subunits are in favor of forming closely π-π stacking to ensure reasonable electron mobilities. Moreover, UFPDI-T and FPDI-T with fused thiophene at outer bay positions possess elevated LUMO energy levels, which can enhance the open circuit voltage (Voc) of devices. FPDI-T based devices display much higher and more balanced hole/electron mobilities. A high power conversion efficiency (PCE) of 7.5% is achieved for FPDI-T based devices, which is much higher than those of UFPDI (4.19%), FPDI (2.95%) and UFPDI-T (4.61%) based ones. Our results demonstrate that simultaneously inner and outer annulation of PDI dimers is a feasible strategy to design high performance PDI-based acceptors.

Highly Efficient Ternary All‐Polymer Solar Cells with Enhanced Stability

AbstractDeveloping organic solar cells (OSCs) based on a ternary active layer is one of the most effective approaches to maximize light harvesting and improve their photovoltaic performance. However, this strategy meets very limited success in all‐polymer solar cells (all‐PSCs) due to the scarcity of narrow bandgap polymer acceptors and the challenge of morphology optimization. In fact, the power conversion efficiencies (PCEs) of ternary all‐PSCs even lag behind binary all‐PSCs. Herein, highly efficient ternary all‐PSCs are realized based on an ultranarrow bandgap (ultra‐NBG) polymer acceptor DCNBT‐TPC, a medium bandgap polymer donor PTB7‐Th, and a wide bandgap polymer donor PBDB‐T. The optimized ternary all‐PSCs yield an excellent PCE of 12.1% with a remarkable short‐circuit current density of 21.9 mA cm−2. In fact, this PCE is the highest value reported for ternary all‐PSCs and is much higher than those of the corresponding binary all‐PSCs. Moreover, the optimized ternary all‐PSCs show a photostability with ≈68% of the initial PCE retained after 400 h illumination, which is more stable than the binary all‐PSCs. This work demonstrates that the utilization of a ternary all‐polymer system based on ultra‐NBG polymer acceptor blended with compatible polymer donors is an effective strategy to advance the field of all‐PSCs.

Benzotriazole Based 2D-conjugated Polymer Donors for High Performance Polymer Solar Cells

To design high efficiency polymer solar cells (PSCs), it is of great importance to develop suitable polymer donors that work well with the low bandgap acceptors, providing complementary absorption, forming interpenetrating networks in the active layers and minimizing energy loss. Recently, we developed a series of two-dimension-conjugated polymers based on bithienylbenzodithiophene-alt-benzotriazole backbone bearing different conjugated side chains, generally called J-series polymers. They are medium energy bandgap (Eg) polymers (Eg of ca. 1.80 eV) with strong absorptions in the range of 400–650 nm, and exhibit ordered crystalline structures, high hole mobilities, and more interestingly, tunable energy levels depending on the structure variations. In this feature article, we highlight our recent efforts on the design and synthesis of those J-series polymer donors, including an introduction on the polymer design strategy and emphasis on the crucial function of differential conjugated side chain. Finally, the future opportunities and challenges of the J-series polymers in PSCs are discussed.

Impact of Chalcogenophenes on Donor-Acceptor Copolymers for Bulk Heterojunction Solar Cells

Three new selenophene-based conjugated copolymers having different ratios of the monomeric units were designed, synthesized and thoroughly characterized. The introduction of an electron-poor and surfaced building moiety like selenathiazole was highly efficient in tuning the bandgap and polymer properties. The chalcogenophene-based medium-bandgap polymers demonstrated low-lying HOMO energy levels (∼5.87 eV), which is benign for use in multi-junction polymer solar cell applications. The representative polymers with heavy atoms revealed the change in electronegativity and atomic size that highly affected the molecular property, its topological features, and photovoltaic properties in polymer solar cells. The selenium-substituted (0.5:0.5) polymer donors showed power conversion efficiencies above 3% when combined with [6,6]-phenyl-C71-butyric acid methyl ester (PC70BM) acceptors in a quintessential bulk-heterojunction solar cell.

Polymer solar cell based on ternary active layer consists of medium bandgap polymer and two non-fullerene acceptors

An efficient PSCs consisting of a ternary active layer containing a medium bandgap conjugated polymer P and two well-known non-fullerene acceptors i.e.ITIC-m and Y6 was fabricated. An overall Power Conversion Efficiency (PCE) of about 15.13% was achieved, with the optimized ternary active layer consisting of 20 wt% of ITIC-m in acceptors i.e.P:ITIC-m:Y6 (1:0.3:1.2). This value is higher than that for the binary counter parts i.e. 12.10% and 13.16% for P:ITIC-m (1:1.5 w:w) and P:Y6 (1:1.5 w:w). The higher short circuit current density of the ternary active layer PSCs is related to the broader absorption spectra as compared to the binary active layer analogs. The open circuit voltage of this ternary active layer-based PSC is in between the PSCs based on P:ITIC-m and P:Y6, which may be related with the Lowest Unoccupied Molecular Orbital (LUMO) energy levels of both the acceptor and which form the alloy between the two acceptors. The overlapping of the absorption band of Y6 with the photoluminescence of ITIC-m confirm the energy transfer from ITIC-m to Y6, leading to the improvement in short circuit current. The balanced charge transport, the reduced charge recombination and the fast charge extraction in the ternary blend lead to the higher value of FF. Thus, all these combined effects lead to the high value of PCE.

Efficient Organic Ternary Solar Cells Employing Narrow Band Gap Diketopyrrolopyrrole Polymers and Nonfullerene Acceptors

Currently, high-performance organic solar cells (OSCs) are mainly composed of narrow band gap (NBG) nonfullerene acceptors and medium band gap (MBG) polymer donors, whereas the solar cells based on NBG polymer donors and MBG nonfullerene acceptors were much less successful. Herein, we report a new diketopyrrolopyrrole (DPP) polymer (PffBT-DPP) with a band gap of 1.33 eV for use in nonfullerene OSCs. When blended with a fullerene acceptor [6, 6]-phenyl C71 butyric acid methyl ester ([70]PCBM) and an MBG nonfullerene acceptor MeIC, the binary OSCs offered a power conversion efficiency (PCE) of 6.8 and 2.0%, respectively. Interestingly, a much higher PCE of 9.0% was achieved for the PffBT-DPP/[70]PCBM/MeIC ternary OSC, which is the sum of the two binary OSCs. The phase-separated morphology in this ternary OSC was characterized and correlated to the device performance. Moreover, the PCE of the ternary OSC is the best result for OSCs employing polymer donors with an optical band gap of <1.40 eV and nonfullerene acceptors. This work demonstrates the potential of constructing high-performance OSCs by employing NBG polymer donors and MBG nonfullerene acceptors.

Side-chain engineering of medium bandgap polymer donors for efficient polymer solar cells

Abstract Polymer solar cells (PSCs) have received widespread attentions recently due to the significant innovations of narrow bandgap n-type organic semiconductor (n-OS) acceptors. To obtain efficient PSCs, it is crucial to employ suitable donor/acceptor pair with matched electronic energy levels, complementary absorption spectra, appropriate molecular self-assembly behavior and preferred blend film morphology, which can be achieved by rational molecular structure optimization. Here we develop three D-A copolymer donors J55, J65 and J75 based on identical building blocks of bithienyl-benzodithiophene (BDTT) D-unit and bifluorine substituted benzotriazole A-unit with different flexible side-chains on BDTT unit to regulate the molecular electronic energy levels and molecular aggregation features, for further improving photovoltaic performance of the PSCs. The three D-A copolymers showed similar absorption profiles due to the identical building blocks. In comparison with the alkyl side-chain substituted polymer J55, the polymers J65 and J75 with alkylthio side-chain and alkylsilyl side-chain showed gradually down-shifted highest occupied molecular orbital energy levels (EHOMO) of −5.38 and −5.43 eV, respectively, which is beneficial for obtaining high open-circuit voltage (Voc). The favorable morphology with preferred face-on orientation and stronger integrated intensity of the π-π stacking peak was formed in J75 blend, which contributes to charge transport, thus enhancing the fill factor (FF) and Jsc. The PSC with J75 as donor and ITIC as acceptor exhibits an efficient PCE of 11.07%, with a Voc of 0.94 V, an enhanced Jsc of 16.99 mA cm−2 and a high FF of 69.29%.

Effects of Monofluorinated Positions at the End-Capping Groups on the Performances of Twisted Non-Fullerene Acceptor-Based Polymer Solar Cells.

Recently, main-chain twisted small molecules are attractive as electron-acceptors in polymer solar cells (PSCs) for their upshifted molecular energy levels, enhanced extinction coefficients, and better charge extraction properties along with longer carrier lifetimes and lower recombination rates relative to their planar analogues, which are conducive to the power conversion efficiency (PCE) promotion of PSCs. To further probe the "structure-performance" correlation of main-chain twisted acceptors, in particular the monofluorine-substituted sites on the performances of the resultant acceptors, two new main-chain twisted small molecules were synthesized, in which a fluorine atom was introduced at different sites on the end-capping group 2-(3-oxo-2,3-dihydro-1H-inden-1-ylidene)malononitrile (INCN). Although fine structural modification was adopted, quite different performances were obtained for the two acceptors. Compared to the 3-fluorinated analogue (i-IEICO-F3), a mixture of 4-fluorinated and 5-fluorinated isomers (i-IEICO-2F) exhibited a higher dipole moment, enlarged molar extinction coefficient with a bathochromic-shifted absorption region, suppressed charge recombinations with balanced charge mobilities, and slightly enhanced crystallinity. In combination with a fluorobenzotriazole-based medium-band gap polymer (J52), a high efficiency of 12.86% was resultantly achieved in an i-IEICO-2F-based device, which is superior to the result (7.65%) of the i-IEICO-F3 device, revealing the importance of monofluorinated positions on the performances of main-chain twisted non-fullerene acceptors.

Manipulating Polymer Donors Toward a High-Performance Polymer Acceptor Based On a Fused Perylenediimide Building Block With a Built-In Twisting Configuration.

A novel fused perylene diimide (PDI)-based polymer electron acceptor (PFPDI-BDF) with a built-in twisting configuration was constructed for application in all-polymer solar cells (all-PSCs). To shed light on the compatibility of the FPDI polymer acceptor and to identify a suitable polymer donor for device applications, we considered herein to investigate three polymer donors (PBDB-T, PTB7-Th, and PCPDTFBT) with different optical and electronic properties as well as polymer chain packing behavior for comparing the device performance. After being fabricated with PFPDI-BDF, polymer donor PBDB-T with a wide band gap showed a decent power conversion efficiency (PCE) of 4.86% with an open-circuit voltage (Voc) of 0.82 V, a short-circuit current density (Jsc) of 8.94 mA cm-2, and a recorded fill factor (FF) of 66.3%, which is one of the best FF reported for PDI-based all-polymer solar cells (all-PSCs). The enhanced efficiency of 6.05% was found in the medium band gap polymer PTB7-Th devices due to the more complementary absorption region that makes the photoactive blends absorb more photons, giving rise to an increased Jsc of 12.97 mA cm-2. On the other hand, due to the inferior exciton dissociation/extraction efficiency and unfavorable morphology compatibility, the narrow band gap polymer donor PCPDTFBT/PFPDI-BDF devices exhibited the worst PCE of only 0.71% with a low Jsc of 2.2 mA cm-2 and a FF of 42.4%.