Control of Multi-Fluorination Number and Position in D-π-A Type Polymers and Their Impact on High-Voltage Organic Photovoltaics.

Exploring the structure-performance relationship of high-voltage organic solar cells (OSCs) is significant for pushing material design and promoting photovoltaic performance. Herein, we chose a D-π-A type polymer composed of 4,8-bis(thiophene-2-yl)-benzo[1,2-b:4,5-b']dithiophene (BDT-T) and benzotriazole (BTA) units as the benchmark to investigate the effect of the fluorination number and position of the polymers on the device performance of the high-voltage OSCs, with a benzotriazole-based small molecule (BTA3) as the acceptor. F00, F20, and F40 are the polymers with progressively increasing F atoms on the D units, while F02, F22, and F42 are the polymers with further attachment of F atoms to the BTA units based on the above three polymers. Fluorination positively affects the molecular planarity, dipole moment, and molecular aggregations. Our results show that VOC increases with the number of fluorine atoms, and fluorination on the D units has a greater effect on VOC than on the A unit. F42 with six fluorine atom substitutions achieves the highest VOC (1.23 V). When four F atoms are located on the D units, the short-circuit current (JSC) and fill factor (FF) plummet, and before that, they remain almost constant. The drop in JSC and FF in F40- and F42-based devices may be attributed to inefficient charge transfer and severe charge recombination. The F22:BTA3 system achieves the highest power conversion efficiency of 9.5% with a VOC of 1.20 V due to the excellent balance between the photovoltaic parameters. Our study provides insights for the future application of fluorination strategies in molecular design for high-voltage organic photovoltaics.

The Development of Quinoxaline-Based Electron Acceptors for High Performance Organic Solar Cells.

In the recent advances of organic solar cells (OSCs), quinoxaline (Qx)-based nonfullerene acceptors (QxNFAs) have attracted lots of attention and enabled the recorded power conversion efficiency approaching 20%. As an excellent electron-withdrawing unit, Qx possesses advantages of many modifiable sites, wide absorption range, low reorganization energy, and so on. To develop promising QxNFAs to further enhance the photovoltaic performance of OSCs, it is necessary to systematically summarize the QxNFAs reported so far. In this review, all the focused QxNFAs are classified into five categories as following: SM-Qx, YQx, fused-YQx, giant-YQx, and polymer-Qx according to the molecular skeletons. The molecular design concepts, relationships between the molecular structure and optoelectronic properties, intrinsic mechanisms of device performance are discussed in detail. At the end, the advantages of this kind of materials are summed up, the molecular develop direction is prospected, the challenges faced by QxNFAs are given, and constructive solutions to the existing problems are advised. Overall, this review presents unique viewpoints to conquer the challenge of QxNFAs and thus boost OSCs development further toward commercial applications.

Optimizing Molecular Crystallinity and Suppressing Electron-Phonon Coupling in Completely Non-Fused Ring Electron Acceptors for Organic Solar Cells.

High open-circuit voltage (Voc) organic solar cells (OSCs) have received increasing attention because of their promising application in tandem devices and indoor photovoltaics. However, the lack of a precise correlation between molecular structure and stacking behaviors of wide band gap electron acceptors has greatly limited its development. Here, we adopted an asymmetric halogenation strategy (AHS) and synthesized two completely non-fused ring electron acceptors (NFREAs), HF-BTA33 and HCl-BTA33. The results show that AHS significantly enhances the molecular dipoles and suppresses electron-phonon coupling, resulting in enhanced intramolecular/intermolecular interactions and decreased nonradiative decay. As a result, PTQ10 : HF-BTA33 realizes a power conversion efficiency (PCE) of 11.42 % with a Voc of 1.232 V, higher than that of symmetric analogue F-BTA33 (PCE=10.02 %, Voc=1.197 V). Notably, PTQ10 : HCl-BTA33 achieves the highest PCE of 12.54 % with a Voc of 1.201 V due to the long-range ordered π-π packing and enhanced surface electrostatic interactions thereby facilitating exciton dissociation and charge transport. This work not only proves that asymmetric halogenation of completely NFREAs is a simple and effective strategy for achieving both high PCE and Voc, but also provides deeper insights for the precise molecular design of low cost completely NFREAs.

Observation of the Therapeutic Effect of Transcutaneous Electrical Stimulation Combined with Pelvic Floor Muscle Training on Post-Radical Prostatectomy Urinary Incontinence.

Objective: Exploring the clinical efficacy of transcutaneous electrical nerve stimulation (TENS) combined with pelvic floor muscle training (PFMT) on post-radical prostatectomy urinary incontinence (PPI). Methods: Eighty patients with post-radical prostatectomy urinary incontinence, who were admitted to Tongji Hospital Affiliated with Tongji University from November 2021 to November 2022, were randomly divided into a TENS group and a PFMT group. The PFMT group received pelvic floor muscle training, while the TENS group received transcutaneous electrical nerve stimulation combined with pelvic floor muscle training. The bladder elevation, urodynamic parameters, pelvic floor muscle strength, treatment outcomes, and treatment efficacy were compared between the two groups of patients after treatment. Results: In the TENS group, the bladder elevation time was shorter and the elevation speed was higher compared with the PFMT group. The TENS group also showed higher values of Qmax, MCC, MUCP, and VLPP than the PFMT group. Furthermore, the TENS group had lower total scores of ICI-Q-SF and less urine pad usage at 72 hours compared with the PFMT group. The treatment efficacy in the TENS group was higher than that in the PFMT group. Conclusion: The combination of TENS and PFMT in PRPUI (Primary Recurrent Pelvic Organ Prolapse with Urinary Incontinence) patients can effectively build up the speed of bladder base elevation, reduce the elevation time, enhance pelvic floor muscle strength, improve patients' urodynamic parameters and urinary incontinence symptoms, and optimize treatment outcomes.

A2 -A1 -D-A1 -A2 -Type Nonfullerene Acceptors.

The A2 -A1 -D-A1 -A2 -type molecules consist of one electron-donating (D) core flanked by two electron-accepting units (A1 and A2 ) and have emerged as an essential branch of nonfullerene acceptors (NFAs). These molecules generally possess higher molecular energy levels and wider optical bandgaps compared with those of the classic A-D-A- and A-DA'D-A-type NFAs, owing to the attenuated intramolecular charge transfer effect. These characteristics make them compelling choices for the fabrication of high-voltage organic photovoltaics (OPVs), ternary OPVs, and indoor OPVs. Herein, the recent progress in the A2 -A1 -D-A1 -A2 -type NFAs are reviewed, including the molecular engineering, structure-property relationships, voltage loss (Vloss ), device stability, and photovoltaic performance of binary, ternary, and indoor OPVs. Finally, the challenges and provided prospects are discussed for the further development of this type of NFAs.

Benzotriazole-Based 3D Four-Arm Small Molecules Enable 19.1 % Efficiency for PM6 : Y6-Based Ternary Organic Solar Cells.

A third component featuring a planar backbone structure similar to the binary host molecule has been the preferred ingredient for improving the photovoltaic performance of ternary organic solar cells (OSCs). In this work, we explored a new avenue that introduces 3D-structured molecules as guest acceptors. Spirobifluorene (SF) is chosen as the core to combine with three different terminal-modified (rhodanine, thiazolidinedione, and dicyano-substituted rhodanine) benzotriazole (BTA) units, affording three four-arm molecules, SF-BTA1, SF-BTA2, and SF-BTA3, respectively. After adding these three materials to the classical system PM6 : Y6, the resulting ternary devices obtained ultra-high power-conversion efficiencies (PCEs) of 19.1 %, 18.7 %, and 18.8 %, respectively, compared with the binary OSCs (PCE=17.4 %). SF-BTA1-3 can work as energy donors to increase charge generation via energy transfer. In addition, the charge transfer between PM6 and SF-BTA1-3 also acts to enhance charge generation. Introducing SF-BTA1-3 could form acceptor alloys to modify the molecular energy level and inhibit the self-aggregation of Y6, thereby reducing energy loss and balancing charge transport. Our success in 3D multi-arm materials as the third component shows good universality and brings a new perspective. The further functional development of multi-arm materials could make OSCs more stable and efficient.

Fused Benzotriazole A-Unit Constructs a D-π-A Polymer Donor for Efficient Organic Photovoltaics.

Herein, we originally developed a fused ring building block as an acceptor unit, namely, 2,6,10-trihydro-carbazole[3,4-c:5,6-c]bis[1,2,5]-triazole (CTA), through fusing two benzotriazoles (BTA) with a pyrrole ring. A p-type polymer PE93 containing the CTA unit exhibits relatively high molecular energy levels and excellent luminescent properties. The PE93:BTA76-based solar cell obtained a device efficiency of 12.16%, with a VOC of 0.94 V and a low nonradiative recombination loss of 0.18 eV. The results suggest that the CTA unit is an efficient acceptor unit to achieve excellent photovoltaic performance.

Dithienobenzothiadiazole (DTBT)-Based Polymers Enable Organic Solar Cells with Ultrahigh VOC of ≈1.3 V.

Dithieno[3',2':3,4;2",3":5,6]benzo[1,2-c][1,2,5]thiadiazole (DTBT) is a newly emerging building block to construct effective photovoltaic polymers. Organic solar cells (OSCs) based on DTBT-based polymers have realized power conversion efficiency (PCEs) over 18%, despite their relatively low open-circuit voltage (VOC ) of 0.8-0.95 V. To extend the application of DTBT-based polymers in high-voltage OSCs, herein, D18-Cl and PE55 are used to combine with a wide-bandgap non-fullerene acceptor (NFA), BTA3, and achieve ultrahigh VOC of 1.30 and 1.28 V, respectively. Compared with D18-Cl based on tricyclic benzodithiophene (BDT) segment, PE55 containing the pentacyclic dithienobenzodithiophene (DTBDT) unit possesses better hole mobility, higher charge-transfer efficiency, and more desirable phase separation. Hence, PE55:BTA3 blend exhibits a higher efficiency of 9.36% than that of D18-Cl: BTA3 combination (6.30%), which is one of the highest values for OSCs at ≈1.3 V VOC . This work attests that DTBT-based p-type polymers are ideal for the application in high-voltage OSCs.

Improving the Photovoltaic Performance of Dithienobenzodithiophene-Based Polymers via Addition of an Additional Eluent in the Soxhlet Extraction Process.

Dithieno[2,3-d;2',3'-d']benzo[1,2-b;4,5-b']dithiophene (DTBDT) is a kind of pentacyclic aromatic electron-donating unit with unique optoelectronic properties, but it has received less attention in the design of photovoltaic polymers. In this work, we copolymerized DTBDT with the electron-deficient unit of dithieno[3',2':3,4;2″,3″:5,6]benzo[1,2-c][1,2,5]thiadiazole (DTBT) and obtained two polymers, PE55 and PE56, with a synergistic heteroatom substitution strategy. When blended with the classic nonfullerene acceptor Y6, PE55 and PE56 achieve power conversion efficiencies (PCEs) of 13.78% and 14.49%, respectively, which indicates that the introduction of sulfur atoms on the conjugated side chain of the D unit is a promising method to enhance the performance of DTBDT-based polymers. Besides, we utilize dichloromethane and chloroform to separate the low molecular weight (Mw) fractions in the solvent extraction process to obtain PE55-CF and PE56-CB, and the PCEs are further improved to 15.00% and 16.11%, respectively. The stronger π-π stacking, optimized blend film morphology, and higher charge mobilities contribute to the enhanced PCEs for polymers with higher Mw obtained via the multistep solvent extraction strategy. Our results not only provide a simple and effective way to improve the photovoltaic performance of conjugated polymers but also imply that some reported polymers purified from the traditional one-step solvent extraction method might be seriously underestimated.

Asymmetric chlorination of A2-A1-D-A1-A2 type non-fullerene acceptors for high-voltage organic photovoltaics.

Herein, we synthesized an asymmetric A2-A1-D-A1-A2 type small molecule nonfullerene acceptor (NFA), HCl-BTA3, by chlorination on one side of A1. The synergistic effect of the asymmetric structure and chlorination endows HCl-BTA3 with a large dipole moment, close molecular packing, and high-efficiency charge transfer and transport. After being blended with a carboxylate-based polymer donor, TTC-Cl, HCl-BTA3 achieved a high open-circuit voltage (VOC) of 1.20 V and a satisfactory power conversion efficiency (PCE) of 11.2%, which are among the highest values for high-voltage carboxylate-based polymers.

Efficacy of Exercise Rehabilitation in Patients with Atrial Fibrillation after Radiofrequency Ablation: A Meta-Analysis of Randomized Controlled Trials.

Background and Aims: Radiofrequency ablation is a commonly used treatment for paroxysmal atrial fibrillation (AF), but postoperative rehabilitation exercises are needed to reverse left ventricular structural and functional abnormalities. This meta-analysis aimed to evaluate the intervention effect of exercise training in patients with AF after radiofrequency ablation. Methods: A systematic literature search was conducted to identify articles in PubMed, MEDLINE, EMBASE, and the Cochrane Library from January 1, 2010 to December 1, 2021. The mean difference with 95% CI was pooled for continuous variables. We used Review Manager 5.3 for the standard meta-analysis. This study followed the guidelines of Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA). Results: Ten randomized controlled trials (RCTs) were included, with a total of 892 patients with AF. The quality of one study was grade A, and the rest were grade B. The results of the meta-analysis showed that the improvement of 6 min walking distance (MD = 34.42, 95% CI: 3.20 to 65.63, P=0.03), peak oxygen uptake (MD = 1.96, 95% CI: 1.14 to 2.78, P < 0.001), left ventricular ejection fraction (LVEF) (MD = 0.09, 95% CI:0.01-0.17, P=0.02), resting heart rate (MD = -4.50, 95% CI: -8.85 to -0.14, P=0.04), and physical component summary (PCS) (MD = 3.00, 95% CI: 0.46 to 5.54, P=0.02) in the experimental group was significantly better than that of the control group, and the difference was statistically significant. Conclusion: Exercise training can improve the level of exercise endurance and cardiac function in patients. However, the results were limited by the quantity and quality of the studies. Large samples and high-quality studies are still needed to verify its long-term efficacy.

Organic Photovoltaic Cells Based on Nonhalogenated Polymer Donors and Nonhalogenated A-DA'D-A-Type Nonfullerene Acceptors with High VOC and Low Nonradiative Voltage Loss.

Compared with other all-inorganic/organic-inorganic hybrid solar cells, the large voltage loss (Vloss) of organic photovoltaic (OPV) cells, especially the nonradiative voltage loss (ΔVnonrad), limited the further improvement of performance. Although A-DA'D-A-type Y-series nonfullerene acceptors (NFAs) largely improve the power conversion efficiencies (PCEs) to 18%, the open-circuit voltage (VOC) of this kind of material was still restricted to below 1.0 V. Herein, we designed and synthesized a narrow bandgap (Eg = 1.41 eV) acceptor BTA77 with an A-DA'D-A-type backbone containing a nonhalogenated terminal group to achieve high electroluminescence efficiency and high VOC. Combined with the nonhalogenated polymer PBDB-T with a conjugated thiophene side chain, BTA77 realized a VOC of 0.944 V, a Vloss of 0.552 V, and a PCE of 13.75%, which is one of the highest PCEs based on nonhalogenated A-DA'D-A-type acceptors with VOC > 0.9 V. After further blending with the nonhalogenated donor polymer PBT1-C with a conjugated phenyl side chain, the VOC increases to 1.021 V with a super low ΔVnonrad of 0.14 V owing to the greatly improved electroluminescence external quantum efficiency (EQEEL) of 4.42 × 10-3. Our results indicate that there is still a large room to decrease the ΔVnonrad and increase VOC by synergistic molecular engineering of p-type polymers and n-type small molecules.

Carboxylate-Containing Wide-Bandgap Polymers for High-Voltage Non-Fullerene Organic Solar Cells.

As one of the polymer modification strategies, carboxylate functionalization has proved effective in downshifting the energy levels and enhancing polymer crystallinity and aggregation. However, high-performance carboxylate-containing polymers are still limited for organic solar cells (OSCs), especially with open-circuit voltage (VOC) above 1.0 V. Herein, we utilize two carboxylate-functionalized wide-band gap (WBG) donor polymers (TTC-F and TTC-Cl) to pair with two WBG electron acceptors (BTA5 and F-BTA5) for high-voltage OSCs. Due to the deeper molecular energy levels, chlorinated polymer TTC-Cl shows higher VOC than fluorinated polymer TTC-F. Furthermore, because of the stronger aggregation in the film, the TTC-Cl-based devices attain suppressed energetic disorders and trap-assisted recombination, decreasing voltage loss and JSC loss. Finally, the TTC-Cl: F-BTA5 blend achieves a higher VOC of 1.17 V and an excellent PCE of 10.98%, one of the best results for high-voltage carboxylate-containing polymers. In addition, the TTC-Cl: BTA5 combination demonstrates the highest VOC of 1.25 V with an ultralow nonradiative energy loss of 0.17 eV. Our results indicate that the carboxylate-containing polymer donors have significant application potential for high-voltage OSCs due to reduced energy loss and improved charge transport and dissociation. Furthermore, the matched absorption spectra with the indoor light sources and low voltage loss promote these material combinations to construct high-performance indoor photovoltaics.

PTB7-Th-Based Organic Photovoltaic Cells with a High VOC of over 1.0 V via Fluorination and Side Chain Engineering of Benzotriazole-Containing Nonfullerene Acceptors.

PTB7-Th is considered one of the most classic donor polymers for organic photovoltaic (OPV) cells. However, the power conversion efficiency (PCE) of PTB7-Th-based OPV is lagging behind that of other promising polymers mainly because of the relatively low open-circuit voltage (VOC). To increase the VOC and PCE of PTB7-Th-based OPV, the development of nonfullerene acceptors (NFAs) and studies of structure-property-performance relationship are vital. Here, three A2-A1-D-A1-A2-type acceptors, namely BTA45, F-BTA45, and F-BTA5, were developed by fluorination on the benzotriazole (BTA) unit and regulating alkoxy or alkyl phenyl side chains. Compared with BTA45, light absorption and π-π packing can be simultaneously improved for the two fluorinated BTA acceptors, resulting in an increased JSC and FF. Moreover, the F-BTA5-based blend film exhibits better phase separation morphology and electron transport than those of BTA45 and F-BTA45, which contribute to a device efficiency of 10.36% with a VOC of 1.03 V. In addition, the ΔE2 values of the three blends are less than 0.15 eV, together with their moderate ΔE3, efficiently decreasing their energy loss. These results highlight the importance of fluorination and side chain engineering for NFAs to boost the VOC and PCE for low-band gap photovoltaic polymers.

The Subtle Structure Modulation of A2 -A1 -D-A1 -A2 Type Nonfullerene Acceptors Extends the Photoelectric Response for High-Voltage Organic Photovoltaic Cells.

Molecular structural modifications are utilized to improve the short-circuit current (JSC ) of high-voltage organic photovoltaics (OPVs). Herein, the classic non-fullerene acceptor (NFA), BTA3, is chosen as a benchmark, with BTA3b containing the linear alkyl chains on the middle core and JC14 fusing thiophene on the benzotriazole (BTA) unit as a contrast. The photovoltaic devices based on J52-F: BTA3b and J52-F: JC14 achieve wider external quantum efficiency responses with band edges of 730 and 800 nm, respectively than that of the device based on J52-F: BTA3 (715 nm). The corresponding  JSC increases to 14.08 and 15.78 mA cm-2 , respectively, compared to BTA3 (11.56 mA cm-2 ). The smaller Urbach energy and higher electroluminescence efficiency guarantee J52-F: JC14 a decreased energy loss (0.528 eV) and a high open-circuit voltage (VOC ) of 1.07 V. Finally, J52-F: JC14 combination achieves an increased power conversion efficiency (PCE) of 10.33% than that of J52-F: BTA3b (PCE = 9.81%) and J52-F: BTA3 (PCE = 9.04%). Overall, the research results indicate that subtle structure modification of NFAs, especially introducing fused rings, is a simple and effective strategy to extend the photoelectric response, boosting the  JSC and ensuring a high VOC beyond 1.0 V.

Effects of Halogenation on the Benzotriazole Unit of Non-Fullerene Acceptors in Organic Solar Cells with High Voltages.

Non-fullerene acceptors (NFAs) can be simply divided into three categories: A-D-A, A-DA'D-A, and A2-A1-D-A1-A2 according to their chemical structures. Benefiting from the easily modified 1,1-dicyanomethylene-3-indanone end groups, the halogenation on the first two types of materials has been proved to be very effective to modulate their optoelectronic properties and improve their photovoltaic performance. Hence, in this work, we systematically investigate the effect of halogenation on the classic NFA molecule of BTA3, which has the linear A2-A1-D-A1-A2-type backbone. After fluorination and chlorination, F-BTA3 and Cl-BTA3 have similar optical band gaps but lower energy levels than BTA3. When blending with a linear copolymer PE25 composed of benzodifuran and chlorinated benzotriazole (BTA) according to "Same-A-Strategy", the corresponding VOC of the halogenated NFAs gradually decreases (1.13 V for F-BTA3 and 1.09 V for Cl-BTA3), compared with that of the BTA3-based device (VOC = 1.22 V). This tendency mainly comes from the lower lowest unoccupied molecular orbital energy levels due to the strong electron-withdrawing ability of halogen atoms and the larger nonradiative energy loss. However, the power conversion efficiencies of the halogenated materials are slightly improved, from 9.08% for PE25: BTA3 to 10.45% for PE25: F-BTA3 and 10.75% for PE25: Cl-BTA, with the nonhalogenated solvent tetrahydrofuran as the processing solvent. The improved photovoltaic performance of F-BTA3 and Cl-BTA3 should come from the higher carrier mobility, weaker bimolecular recombination, and higher fluorescence quenching rate. This study illustrates that halogenation on the A1 unit is a promising strategy for developing novel and effective A2-A1-D-A1-A2-type NFAs.

Tricyclic or Pentacyclic D Units: Design of D-π-A-Type Copolymers for High VOC Organic Photovoltaic Cells.

Although there are several electron-donating (D) units, only the classic benzo[1,2-b:4,5-b']dithiophenes (BDT) unit was utilized to develop D-π-A-type copolymers for high-voltage organic photovoltaic (OPV) cells. Hence, in this work, we chose two tricyclic D units, BDT and benzo[1,2-b:4,5-b']difurans (BDF), together with one pentacyclic ring, dithieno[2,3-d;2',3'-d']benzo[1,2-b;4,5-b']dithiophenes (DTBDT), to comprehensively study the effect of different D units on the optoelectronic properties and photovoltaic performance. By copolymerized with the benzo[1,2,3]triazole (BTA) electron-accepting unit, the final copolymers J52-Cl, F11, and PE52 were combined with a nonfullerene acceptor (NFA) F-BTA3 according to the "Same-A-Strategy." As we preconceived, all the three single-junction OPV cells can obtain high open-circuit voltage (VOC) over 1.10 V. Although the tricyclic D unit of BDF exhibits a slightly lower VOC of 1.12 V because of its mildly larger energy loss of 0.698 eV, its higher carrier mobilities and exciton dissociation efficiency strikingly boost the short-circuit current (JSC) and fill factor, which contribute to a comparable PCE of 10.04% with J52-Cl (10.10%). However, the DTBDT-based polymer PE52 shows the worst performance with a PCE of 6.78% and a VOC of 1.14 V, owing to the higher bimolecular recombination and disordered molecular stacking. Our results indicate that tricyclic D units should be a better choice for constructing D-π-A-type polymers for high-voltage photovoltaic materials than the pentacyclic analogues.

Fabrication of High VOC Organic Solar Cells with a Non-Halogenated Solvent and the Effect of Substituted Groups for "Same-A-Strategy" Material Combinations.

We report a class of high-voltage organic solar cells (OSCs) processed by the environmentally friendly solvent tetrahydrofuran (THF), where four benzotriazole (BTA)-based p-type polymers (PE31, PE32, PE33, and J52-Cl) and a BTA-based small molecule BTA5 are applied as p-type and n-type materials, respectively, according to "Same-A-Strategy" (SAS). The single-junction OSCs based on all four material blends exhibit a high open-circuit voltage (VOC) above 1.10 V. We systematically study the impact of the three different substituents (-OCH3, -F, -Cl) on the BTA unit of the polymer donors. Interestingly, PE31 containing the unsubstituted BTA unit shows the efficient hole transfer and more balanced charge mobilities, thus leading to the highest power conversion efficiency (PCE) of 10.08% with a VOC of 1.11 V and a JSC of 13.68 mA cm-2. Due to the upshifted highest electron-occupied molecular orbital (HOMO) level and the weak crystallinity of the methoxy-substituted polymer PE32, the resulting device shows the lowest PCE of 7.40% with a slightly decreased VOC of 1.10 V. In addition, after the chlorination and fluorination, the HOMO levels of the donor materials PE33 and J52-Cl are gradually downshifted, contributing to increased VOC values of 1.16 and 1.21 V, respectively. Our results prove that an unsubstituted p-type polymer can also afford high voltage and promising performance via non-halogenated solvent processing, which is of great significance for simplifying the synthesis steps and realizing the commercialization of OSCs.

Side-chain engineering of copolymers based on benzotriazole (BTA) and dithieno[2,3-d;2',3'-d']benzo[1,2-b;4,5-b']dithiophenes (DTBDT) enables a high PCE of 14.6.

Dithieno[2,3-d;2',3'-d']benzo[1,2-b;4,5-b']dithiophenes (DTBDT) is a kind of prospective candidate for constructing donor-π-acceptor (D-π-A) copolymer donors applied in organic solar cells but is restricted due to its relatively poor photovoltaic performance compared with benzo[1,2-b;4,5-b']dithiophenes (BDT)-based analog. Herein, three conjugated polymers (PE51,PE52andPE53)-based DTBDT and benzo[d][1,2,3]triazole (BTA) bearing different lengths of alkyl side chain were designed and synthesized. The change in alkyl chain length can obviously affect the energy level distribution, molecular stacking, miscibility and morphology with the non-fullerene acceptor ofY6. PolymerPE52with a moderate alkyl chain realized the highest short-current density (JSC) and fill factor (FF) of 25.36 mA cm-2and 71.94%, respectively. Compared with BDT-based analogJ52-Cl, the significantly enhanced crystallinity and intermolecular interaction ofPE52had effectively boosted the charge transport characteristic and optimized the surface morphology, thereby increasing the power conversion efficiency from 12.3% to an impressive 14.6%, which is the highest value among DTBDT-based and BTA-based polymers. Our results show that not only could high efficiency be achieved via using DTBDT as a D unit, but the length of the alkyl chain on BTA has a significant impact on the photovoltaic performance.

Solution-Processed Organic Solar Cells with High Open-Circuit Voltage of 1.3 V and Low Non-Radiative Voltage Loss of 0.16 V.

Compared with inorganic or perovskite solar cells, the relatively large non-radiative recombination voltage losses (ΔVnon-rad ) in organic solar cells (OSCs) limit the improvement of the open-circuit voltage (Voc ). Herein, OSCs are fabricated by adopting two pairs of D-π-A polymers (PBT1-C/PBT1-C-2Cl and PBDB-T/PBDB-T-2Cl) as electron donors and a wide-bandgap molecule BTA3 as the electron acceptor. In these blends, a charge-transfer state energy (ECT ) as high as 1.70-1.76 eV is achieved, leading to small energetic differences between the singlet excited states and charge-transfer states (ΔECT ≈ 0.1 eV). In addition, after introducing chlorine atoms into the π-bridge or the side chain of benzodithiophene (BDT) unit, electroluminescence external quantum efficiencies as high as 1.9 × 10-3 and 1.0 × 10-3 are realized in OSCs based on PBTI-C-2Cl and PBDB-T-2Cl, respectively. Their corresponding ΔVnon-rad are 0.16 and 0.17 V, which are lower than those of OSCs based on the analog polymers without a chlorine atom (0.21 and 0.24 V for PBT1-C and PBDB-T, respectively), resulting in high Voc of 1.3 V. The ΔVnon-rad of 0.16 V and Voc of 1.3 V achieved in PBT1-C-2Cl:BTA3 OSCs are thought to represent the best values for solution-processed OSCs reported in the literature so far.