Wide-bandgap Polymer Research Articles

A low-cost wide bandgap polymer based on carboxylate substituted thiazole enables efficient organic solar cells with remarkable batch-to-batch reproducibility

A low-cost wide bandgap polymer based on carboxylate substituted thiazole enables efficient organic solar cells with remarkable batch-to-batch reproducibility

A Fluorinated Imide-Functionalized Arene Enabling a Wide Bandgap Polymer Donor for Record-Efficiency All-Polymer Solar Cells.

All-polymer solar cells (all-PSCs) present compelling advantages for commercial applications, including mechanical durability and optical and thermal stability. However, progress in developing high-performance polymer donors has trailed behind the emergence of excellent polymer acceptors. In this study, we report a new electron-deficient arene, fluorinated bithiophene imide (F-BTI) and its polymer donor SA1, in which two fluorine atoms are introduced at the outer β-positions in the thiophene rings of BTI to fine-tune the energy levels and aggregation of the resulting polymers. SA1 exhibits a deep HOMO level of -5.51 eV, a wide bandgap of 1.81 eV and suitable miscibility with the polymer acceptor. Polymer chains incorporating F-BTI result in a highly ordered π-π stacking and favorable phase-separated morphology within the all-polymer active layer. Thus, SA1 : PY-IT-based all-PSCs exhibit an efficiency of 16.31 % with excellent stability, which is further enhanced to a record value of 19.33 % (certified: 19.17 %) by constructing ternary device. This work demonstrates that F-BTI offers an effective route for developing new polymer materials with improved optoelectronic properties, and the emergence of F-BTI will change the scenario in terms of developing polymer donor for high-performance and stable all-PSCs.

A Fluorinated Imide‐Functionalized Arene Enabling a Wide Bandgap Polymer Donor for Record‐Efficiency All‐Polymer Solar Cells

AbstractAll‐polymer solar cells (all‐PSCs) present compelling advantages for commercial applications, including mechanical durability and optical and thermal stability. However, progress in developing high‐performance polymer donors has trailed behind the emergence of excellent polymer acceptors. In this study, we report a new electron‐deficient arene, fluorinated bithiophene imide (F‐BTI) and its polymer donor SA1, in which two fluorine atoms are introduced at the outer β‐positions in the thiophene rings of BTI to fine‐tune the energy levels and aggregation of the resulting polymers. SA1 exhibits a deep HOMO level of −5.51 eV, a wide bandgap of 1.81 eV and suitable miscibility with the polymer acceptor. Polymer chains incorporating F‐BTI result in a highly ordered π–π stacking and favorable phase‐separated morphology within the all‐polymer active layer. Thus, SA1 : PY‐IT‐based all‐PSCs exhibit an efficiency of 16.31 % with excellent stability, which is further enhanced to a record value of 19.33 % (certified: 19.17 %) by constructing ternary device. This work demonstrates that F‐BTI offers an effective route for developing new polymer materials with improved optoelectronic properties, and the emergence of F‐BTI will change the scenario in terms of developing polymer donor for high‐performance and stable all‐PSCs.

Efficient Synthesis of High-Performance Wide-Bandgap Polymers Based on Difluoronaphthodithiophene: Fluorination Position Impact on Photovoltaic Performance

Efficient Synthesis of High-Performance Wide-Bandgap Polymers Based on Difluoronaphthodithiophene: Fluorination Position Impact on Photovoltaic Performance

Dual-Band Photomultiplication-Type Organic Photodetectors with Ultrahigh Signal-to-Noise Ratios.

A series of dual-band photomultiplication (PM)-type organic photodetectors (OPDs) were fabricated by employing a donor(s)/acceptor (100:1, wt/wt) mixed layer and an ultrathin Y6 layer as the active layers, as well as by using PNDIT-F3N as an interfacial layer near the indium tin oxide (ITO) electrode. The dual-band PM-type OPDs exhibit the response range of 330-650 nm under forward bias and the response range of 650-850 nm under reverse bias. The tunable spectral response range of dual-band PM-type OPDs under forward or reverse bias can be explained well from the trapped electron distribution near the electrodes. The dark current density (JD) of the dual-band PM-type OPDs can be efficiently suppressed by employing PNDIT-F3N as the anode interfacial layer and the special active layers with hole-only transport characteristics. The light current density (JL) of the dual-band PM-type OPDs can be slightly increased by incorporating wide-bandgap polymer P-TPDs with relatively large hole mobility (μh) in the active layers. The signal-to-noise ratios of the optimized dual-band PM-type OPDs reach 100,980 under -50 V bias and white light illumination with an intensity of 1.0 mW·cm-2, benefiting from the ultralow JD by employing wide-bandgap PNDIT-F3N as the anode interfacial buffer layer and the increased JL by incorporating appropriate P-TPD in the active layers.

Wide Bandgap Polymer Donors Based on Succinimide-Substituted Thiophene for Nonfullerene Organic Solar Cells.

The advent of nonfullerene acceptors (NFAs) has greatly improved the photovoltaic performance of organic solar cells (OSCs). However, to compete with other solar cell technologies, there is a pressing need for accelerated research and development of improved NFAs as well as their compatible wide bandgap polymer donors. In this study, a novel electron-withdrawing building block, succinimide-substituted thiophene (TS), is utilized for the first time to synthesize three wide bandgap polymer donors: PBDT-TS-C5, PBDT-TSBT-C12, and PBDTF-TSBT-C16. These polymers exhibit complementary bandgaps for efficient sunlight harvesting and suitable frontier energy levels for exciton dissociation when paired with the extensively studied NFA, Y6. Among these donors, PBDTF-TSBT-C16 demonstrates the highest hole mobility and a relatively low highest occupied molecular orbital (HOMO) energy level, attributed to the incorporation of thiophene spacers and electron-withdrawing fluorine substituents. OSC devices based on the blend of PBDTF-TSBT-C16:Y6 achieve the highest power conversion efficiencyof 13.21%, with a short circuit current density (Jsc) of 26.83mA cm-2, an open circuit voltage (Voc) of 0.80V, and a fill factorof 0.62. Notably, the Voc × Jsc product reaches 21.46mW cm-2, demonstrating the potential of TS as an electron acceptor building block for the development of high-performance wide bandgap polymer donors in OSCs.

Wide Bandgap Polymer Donors Containing Dihalovinyl Thiophene Building Blocks for Organic Solar Cells

Wide Bandgap Polymer Donors Containing Dihalovinyl Thiophene Building Blocks for Organic Solar Cells

Wide-bandgap donor polymers from organic photovoltaics as dopant-free hole transport layers for perovskite solar cells

Dopant-free polymer hole transport materials (HTMs) exhibit high thermal stability, hydrophobicity and film-processing capabilities, demonstrating excellent device efficiency and stability in perovskite solar cells (PSCs). Continued innovation of wide-bandgap polymers in organic photovoltaics (OPV) provides a valuable toolbox for developing polymeric HTMs. Here, we propose an effective molecule design for selecting structurally relevant polymers (D18, D18-Cl, PBQx-TCl) available for commercialization. We discover that the highly planar conjugated backbones play a crucial role in regulating the packing orientation of the film relative to the perovskite. The moderate aggregation with face-on packing orientation is conducive to the high-quality film, which is responsible for better contact with perovskite and superior charge extraction and transport. Simultaneously, these polymers with robust passivation enhanced the open circuit voltage (VOC) without additional passivation layers, streamlining the device process. Consequently, a PSC using dopant-free PBQx-TCl HTL demonstrated an efficiency of 24.12 % with a high VOC of 1.20 V and good operational stability (T90 > 600 h). This work reveals transparent structure–function-performance relationships between molecules and devices, paving the way for the subsequent development of high-performance HTMs.

Efficient and Stable All-Polymer Solar Cells Enabled by Dual Working Mechanism.

Ternary strategy with integration characteristics and adaptability is a simple and effective method for blooming of the performance of photovoltaic devices. Herein, a novel wideband gap polymer donor PBB2-Hs is synthesized as the guest component to optimize all-polymer solar cells (all-PSCs). High-energy photon absorption and long exciton lifetime of PBB2-Hs constitute efficient energy transfer. Good miscibility and cascade energy levels promote the formation of alloy-like structure between PBB2-Hs and host system. The dual working mechanisms greatly improve photon capture and charge transfer in active layers. Additionally, the introduction of PBB2-Hs also optimizes the ordered molecular stacking of acceptors and suppresses molecular peristalsis. Upon adding 15 wt% PBB2-Hs, the ternary all-PSC achieved a champion efficiency of 17.66%, and can still maintain 82% photostability (24h) and 91% storage stability (1000h) of the original PCE. Moreover, the strong molecular stacking and entanglement between PBB2-Hs and the host material increased the elongation at break of ternary blend film by 1.6 times (16.2%), allowing the flexible device to maintain 83% of the original efficiency after 800 bends (R = 5mm). This work highlights the effectiveness of guest polymer on simultaneously improving photovoltaic performance, photostability and mechanical stability in all-PSCs.

Efficient Dual Mechanisms Boost the Efficiency of Ternary Solar Cells with Two Compatible Polymer Donors to Exceed 19.

Ternary strategyopens a simple avenue to improve the power conversion efficiency (PCE) of organic solar cells (OSCs). The introduction of wide bandgap polymer donors (PDs) as third component canbetter utilize sunlight andimprove the mechanical and thermal stability of active layer. However, efficient ternary OSCs (TOSCs) with two PDs are rarely reported due to inferior compatibility and shortage of efficient PDs match with acceptors. Herein, two PDs-(PBB-F and PBB-Cl) are adopted in the dual-PDs ternary systems to explore the underlying mechanisms and improve their photovoltaic performance. The findings demonstrate that the third components exhibit excellent miscibility with PM6 and are embedded in the host donor to form alloy-like phase. A more profound mechanism for enhancing efficiency through dual mechanisms, that are the guest energy transfer to PM6 and charge transport at the donor/acceptor interface, has been proposed. Consequently, the PM6:PBB-Cl:BTP-eC9 TOSCs achieve PCE of over 19%. Furthermore, the TOSCs exhibit better thermal stability than that of binary OSCs due to the reduction in spatial site resistance resulting from a more tightly entangled long-chain structure. This work not only provides an effective approach to fabricate high-performance TOSCs, but also demonstrates the importance of developing dual compatible PD materials.

Isomerization of Benzothiadiazole Yields a Promising Polymer Donor and Organic Solar Cells with Efficiency of 19.0.

The exploration of high-performance and low-cost wide-bandgap polymer donors remains critical to achieve high-efficiency nonfullerene organic solar cells (OSCs) beyond current thresholds. Herein, the 1,2,3-benzothiadiazole (iBT), which is an isomer of 2,1,3-benzothiadiazole (BT), is used to design wide-bandgap polymer donor PiBT. The PiBT-based solar cells reach efficiency of 19.0%, which is one of the highest efficiencies in binary OSCs. Systemic studies show that isomerization of BT to iBT can finely regulate the polymers' photoelectric properties including i) increasing the extinction coefficient and photon harvest, ii) downshifting the highest occupied molecular orbital energy levels, iii) improving the coplanarity of polymer backbones, iv) offering good thermodynamic miscibility with acceptors. Consequently, the PiBT:Y6 bulk heterojunction (BHJ) device simultaneously reaches advantageous nanoscale morphology, efficient exciton generation and dissociation, fast charge transportation, and suppressed charge recombination, leading to larger VOC of 0.87V, higher JSC of 28.2 mA cm-2, greater fill factor of 77.3%, and thus higher efficiency of 19.0%, while the analog-PBT-based OSCs reach efficiency of only 12.9%. Moreover, the key intermediate iBT can be easily afforded from industry chemicals via two-step procedure. Overall, this contribution highlights that iBT is a promising motif for designing high-performance polymer donors.

High-efficiency D-D-type wide bandgap polymer donor based on dibenzopyran unit

Pyran units as a six-membered heterocyclic nonaromatic containing one sp3 hybridized carbon and an oxygen have been widely employed to exploit donor and acceptor materials, and excellent power conversion efficiencies (PCEs) can be achieved for polymer solar cells (PSCs). In this work, a dibenzopyran (DBP) building block and a benzodithiophene (BDT) derivative as donor unit were utilized to successfully prepare a novel donor–donor (D-D)-type wide bandgap polymer PBDBP. The polymer PBDBP possesses an ultra-wide optical bandgap of 2.18 eV due to the weak intramolecular charge-transfer effect. Meanwhile, a low-lying HOMO energy of −5.41 eV is achieved, which is beneficial to realize a high Voc. Additionally, PBDBP also exhibits a complementary absorption with a narrow bandgap Y6 ranging from 300 to 950 nm, which can facilitate to improve light-harvesting ability for high Jsc. Finally, PBDBP:Y6 based device exhibits a high PCE of 11.43 % (Voc = 0.89 V, Jsc = 23.14 mA/cm2, and FF = 55.66 %). Our research indicates that the D-D-type polymer PBDBP based on dibenzopyran unit is a promising wide bandgap donor material for PSCs.

Highly crystalline polycyclic aromatic lactam-based regioregular wide-band gap polymer donors for organic solar cells

The design of wide-band gap polymer donors with complementary absorption to non-fullerene acceptors (NFAs) is essential to increase the photovoltaic efficiency of organic solar cells (OSCs).

18.6% Efficiency All-Polymer Solar Cells Enabled by a Wide Bandgap Polymer Donor Based on Benzo[1,2-d:4,5-d']bisthiazole.

The limited selection of wide bandgap polymer donors for all-polymer solar cells (all-PSCs) is a bottleneck problem restricting their further development and remains poorly studied. Herein, a new wide bandgap polymer, namely PBBTz-Cl, is designed and synthesized by bridging the benzobisthiazole acceptor block and chlorinated benzodithiophene donor block with thiophene units for application as an electron donor in all-PSCs. PBBTz-Cl not only possesses wide bandgap and deep energy levels but also displays strong absorption, high-planar structure, and good crystallinity, making it a promising candidate for application as a polymer donor in organic solar cells. When paired with the narrow bandgap polymer acceptor PY-IT, a fibril-like morphology forms, which facilitates exciton dissociation and charge transport, contributing to a power conversion efficiency (PCE) of 17.15% of the corresponding all-PSCs. Moreover, when introducing another crystalline polymer acceptor BTP-2T2F into the PBBTz-Cl:PY-IT host blend, the absorption ditch in the range of 600-750nm is filled, and the blend morphology is further optimized with the trap density reducing. As a result, the ternary blend all-PSCs achieve a significantly improved PCE of 18.60%, which is among the highest values for all-PSCs to date.

Effect of diazine isomers on photovoltaic properties of simple and efficient wide band gap polymer donor materials

In this paper, we designed and synthesized six new wide band gap donor-acceptor (D-A) copolymers, PZ2-PZ7, with diazine isomers (pyrazine, pyridazine, pyrimidine) as the A unit and alkylthiophene- or alkylthiothienyl-substituted BDT as the D unit. The effect of diazine isomeric A units and side-chain substituents on molecular structure, optoelectronic properties and photovoltaic performances of the resulting D-A copolymers were investigated in details. Six low-cost polymers were easily obtained by minimal reaction steps and cheap raw materials. All the polymers exhibited wide band gaps (WBGs) (>1.9 eV) and deep-lying HOMO energy levels (<−5.48 eV), which is convenient for paring with low band gap nonfullerene acceptors (NFAs). Theoretical simulation calculation indicates that diazine isomeric A unit has great impact on the planarity of polymer backbone. Bulk heterojunction polymer solar cells (PSCs) were fabricated with these polymers as donor materials and representative NFAs (Y6 and ITIC) as acceptor materials. After optimization, pyrazine-based polymers PZ2 and PZ3 exhibited higher PCEs than those of pyridazine- and pyrimidine-based ones (PZ4-PZ7) regardless of the acceptors. Finally, the PZ2:Y6-based PSC achieved the highest power conversion efficiency (PCE) up to 11.21 %, which could be attributed to more balanced carrier mobility, increased charge dissociation probability, reduced charge recombination, and superior active layer morphology. This work suggests that diazine-based WBG polymers, especially for pyrazine, would become as very promising donor candidates for constructing low-cost and efficient NFA-based PSCs.

Simultaneously improved Jsc and Voc achieving 19.15% efficiency in ternary blend polymer solar cell containing a Y-type acceptor with thiophene based end groups

Simultaneously enhancing the short-circuit current density (Jsc) and open-circuit voltage (Voc) of current state-of-the-art polymer solar cells (PSCs) containing wide bandgap polymers as donors and Y6 derivatives as acceptors is of great challenge but essential for further improvement of the photovoltaic performances. In this work, two Y-type non-fullerene acceptors of BTP-T and BTP-TCl were designed and successfully synthesized with relatively weak electron-accepting thiophene based end groups, where blue-shifted absorption and upshifted LUMO energy levels were achieved to fill the well-known absorption gap at 700 nm of typical binary devices based Y-type molecules and rise the output voltage, respectively. Simultaneously increased Jsc and Voc were achieved in ternary blend devices containing D18:BTP-eC9:BTP-TCl with a significantly improved PCE up to 19.15 %, which is over 7 % increase compared to the binary device. Our results illustrated the great potential of rational design of Y6 derivatives for constructing ternary PSCs to improve their performances.

High mobility wide bandgap polymer realized by a combined modification strategy of processing solvent and dielectric interface

High mobility organic thin film transistors (OTFTs) are realized through a combined modification strategy of processing solvent and dielectric interface when a wide bandgap donor-acceptor conjugated polymer PBODT with edge-on orientation and high crystallinity was applied. The pre-aggregation ability of PBODT in different solvents exhibits different crystallinity but remains typical edge-on orientation. Moreover, the surface energy modulation of the semiconductor/dielectric interface enhances the transport property of PBODT, delivering a high mobility of 3.68 cm2V−1s−1. In addition, a comparable mobility of 3.06 cm2V−1s−1 is demonstrated via the eco-friendly solvent mesitylene. The results have demonstrated that the synergy of solvent and dielectric interface can provide new vitality for the application of high-performance environmentally friendly OTFTs.

NIR-absorbing polymer acceptor for efficient all-polymer solar cells with a record-high photocurrent of 26.5 ​mA ​cm−2

Achieving high short-circuit current density (JSC) to boost power conversion efficiency (PCE) of all-polymer solar cells (all-PSCs) is a major challenge, mainly due to the difficulty in developing high-performance near-infrared (NIR)-absorbing polymer acceptors. Herein, a new polymer acceptor named PY2Se–4F employing a Y-series small-molecule acceptor as the precursor is designed and synthesized. Thanks to its unique molecular backbone structure combining selenophene-fused central core and bi-fluorinated end-group, PY2Se–4F shows desirable NIR-absorption with a spectral onset approaching 1000 ​nm, which is beneficial for obtaining high JSC when matched with wide bandgap polymer donors such as PM6 and D18. For the binary all-PSCs, PM6:PY2Se–4F delivers a record-high JSC of 26.5 ​mA ​cm−2, which is superior to that of D18:PY2Se–4F, mainly due to stronger absorption in the range of 600–700 ​nm. In contrast, the D18:PY2Se–4F combination exhibits more favorable blend morphology, higher and more balanced charge-transporting, and less non-radiative energy loss compared with the PM6:PY2Se–4F. As a result, the D18:PY2Se–4F-based devices offer an improved PCE of 16.1 ​% with a JSC of 25.5 ​mA ​cm−2 and both higher photovoltage and fill factor, while the related PCE and JSC are ones of the top values among the reported binary all-PSCs. The results indicate that PY2Se–4F is a promising NIR-absorbing polymer acceptor for obtaining efficient all-PSCs with record-high JSC.

Trifluoromethylation in the Design and Synthesis of High-Performance Wide Bandgap Polymer Donors for Quasiplanar Heterojunction Organic Solar Cells.

New strategies for the molecular design to construct efficient electron-deficient units for D-A-type donor copolymers are urgently needed. Halogenation of electron-deficient units (A) has been shown to be the most effective strategy reported to date with which to produce high-performance donor polymers. Herein, we have constructed two different trifluoromethyl-substituted polymer donors, PBQP-CF3 and PBQ-CF3. The trifluoromethylation process typically involves complex protocols, which are not widely used in the synthesis of polymer donors. Accordingly, we have developed a single-step, one-pot synthesis of the new trifluoromethyl-substituted electron-deficient unit (A) of PBQ-CF3. The strong electron-withdrawing ability of the trifluoromethyl group ensures deeper highest occupied molecular orbital (HOMO) energy levels, and the non-covalent bonding interactions of the fluorine atoms are beneficial to the regulation of aggregation properties. Thus, both of the trifluoromethyl-substituted polymer donors obtained much higher power conversion efficiency (PCE) than PBDP-H (6.66%). PBQ-CF3 exhibits a deeper HOMO energy level, better aggregation behavior, and higher hole mobility than PBQP-CF3. PBQ-CF3-based quasiplanar heterojunction (Q-PHJ) devices therefore achieve simultaneously enhanced open-circuit voltage (VOC), short-circuit current density (JSC), and fill factor (FF) and an impressive PCE (16.02%), which is much higher than that obtained by PBQP-CF3-based devices (12.57%). This work reveals a promising path to synthesis of the trifluoromethylation polymer donors and demonstrates that the trifluoromethylation strategy can be used to enhance the photovoltaic performance.

An effective strategy to design high-performance wide bandgap polymer donors for organic solar cells by increasing the backbone curvature

Although wide bandgap (WBG) polymer donors are widely used in non-fullerene organic solar cells (OSCs), only a few WBG polymers exhibited high power conversion efficiencies (PCEs). Developing WBG donors with ideal complementary absorption with narrow bandgap non-fullerene acceptors is critical to further improving the photovoltaic performance of OSCs. Here, we provide an effective strategy to widen the bandgap (Eg) of polymers by increasing the curvature of the polymer donor backbone structure and compare it with the fluorination strategy. Both experimental and theoretical results demonstrated that the fluorination strategy reduced the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) of PBDT-DT2FBT with little effect on the Eg. In contrast, the polymer PBDT-DTfBT, with a large backbone curvature, exhibited a reduced HOMO energy level and a significantly increased LUMO energy level, resulting in a significant increase in the optical Eg of 0.19 eV. The PBDT-DTfBT-based device achieved a high PCE of 15.89%, which far exceeded the PCEs of the PBDT-DTBT (9.84%) and PBDT-DT2FBT-based devices (8.02%). This work could guide the design of high-performance WBG donors.