Wen Wang

Ternary strategies are effective approaches to boost solar cell performance by introducing a third component as the guest, while selection of the simple component is yet a key issue. Herein, a low-cost dithienophthalimide (DPI)-based wide-bandgap polymer donor PBDT(8,10)-DPI(4,6) was selected as a third component for the host PM6:BTP-eC9 system. The effects of the third component on the optical and electrical properties, photovoltaic performance, and thin-film structure were explored. By incorporating a small amount of PBDT(8,10)-DPI(4,6) into the PM6:BTP-eC9 host, a broader absorption range, a cascaded energy level alignment, and a more favorable active layer morphology are achieved in ternary devices, leading to an improved short-circuit current density and fill factor. As a result, a PCE of 18.15% with a VOC of 0.86 V, a JSC of 27.35 mA cm–2, and an FF of 77.01% was ultimately achieved in the ternary device after adding 5% PBDT(8,10)-DPI(4,6), surpassing the efficiency (17.26%) of the control binary device. Meanwhile, the effect of the third component on device stability was investigated, revealing notable enhancements in overall stability (photostability, thermal stability, and storage stability) for the ternary devices. Thus, dithienophthalimide (DPI)-based polymer donors would be expected to be effective third components for efficient and stable organic solar cells.

Non-halogenated low-toxicity polymers demonstrate significant commercialization potential for organic solar cells (OSCs), owing to their advantageous processing characteristics. However, high-performance non-halogenated polymer donors are still limited. Herein, dithienophthalimide (DPI)-based monomers bearing various side chains have been synthesized at low cost. And then, a series of BDT-DPI-based non-halogenated polymer donors (PBDT-DPIs) were designed and obtained by synergistically tuning the alkyl side chains on both DPI and BDT units, in which thiophene served as a π-bridge, BDT with various side chains (R₁) served as the D unit, and DPI with various side chains (R₂) served as the A unit. The effects of alkyl side chains on the polymers’ optical absorption spectra, electronic and morphological properties, and photovoltaic performance were investigated to understand the relationship between the structure and photovoltaic (PV) performance. It is found that alkyl side chain lengths have negligible impact on optical absorption spectra due to their same backbones, but have profound effects on their aggregation and crystallinity in the solid state. The length of alkyl side chains has a significant influence on the active layer morphology, charge transport properties, and device performance when blended with the non-fullerene acceptor BTP-eC9. As a result, through fine-tuning the alkyl side chains, a PBDT_(8,10)-DPI_(4,6)-based device exhibited the highest PCE of 14.56%, with an open-circuit voltage of 0.85 V, a short-circuit current density of 24.76 mA cm⁻², and a fill factor of 69.05%. Our study demonstrated that tailoring the side chain on both BDT and DPI units could optimize crystallinity, aggregation and miscibility for developing high-performance non-halogenated polymer donors.

In the past decade, the study on organic solar cells (OSCs) has made great progress. For commercial application, achieving high efficiency OSCs with the prominent stability is a crucial issue. Here, two crosslinkable vinyl-functionalized D–A–D–D₁-type polymers PM6-Ax (x: 5 or 15) were successfully synthesized by introducing a crosslinkable benzodithiophene (D₁) unit with vinyl functionality into the D–A polymer PM6. As expected, the un-crosslinked PM6-A5:Y6-based OSC process an outstanding PCE (15.20%) without additives, which is higher than that of the reference PM6:Y6-based OSCs (13.65%) by the D–A–D–D₁ strategy. It is found that polymers PM6-Ax can be crosslinked to some extent after annealing at 150 °C for a certain period of time. Meanwhile, by thermal crosslinking of the active layer, the PM6-Ax:Y6-based devices were fabricated and the stability was studied. Reference PM6:Y6-based devices were also fabricated. As a result, crosslinked PM6-A5:Y6-based devices retained 91.0% of the initial PCE under 48 h of continuous 60 °C thermal aging and 92.8% of the initial PCE under 72 h continuous white LED light illumination, whereas the reference PM6:Y6-based devices retained 81.9% and 72.7% under the same aging conditions. Moreover, crosslinked PM6-A5:Y6-based devices showed superior shelf-life stability over the reference devices. These results demonstrate that crosslinking of the PM6-A5:Y6-based active layer can significantly boost overall stability (including thermal-stability, photo-stability, and storage-stability) of the OSCs.

We developed novel D–A–D–D₁-type polymers with unequal D and A units by incorporating a third component into the backbone of PM6 for enhanced short-circuit current density.

A series of novel praseodymium (Pr)-bonded polymers with fluorene, phthalimide and phenanthroline moieties in the main chain were synthesized via the coordination reaction and palladium-catalyzed Suzuki coupling reaction. The resistive switching devices with the configuration ITO/Polymer/Al exhibited nonvolatile write-once-read-many-times (WORM) memory behavior. The introduction of Pr complex into the polymer main chain played a key role in the memory performance of the devices.

.All-polymer solar cells (all-PSCs) can offer unique merits of high morphological stability to thermal and mechanical stress. To realize its full potential as flexible or wearable devices, it is highly desirable that the all-PSCs can be fabricated from green solvent with simple post-treatment to avoid thermal annealing on flexible substrate. This proposed a severely challenge on material design to tune their properties with suitable solubility, aggregation, and morphology. To address this challenge, here, a simple bicomponent-random approach on a D-A-type polymer donor was developed by just varying the D-A molar ratio. Under this approach, a series of new random polymers PBDTa-TPDb with different molar ratio of D component of 2D-benzo[1,2-b:4,5-b']dithiophene (BDT) and A component of thieno[3,4-c]pyrrole-4,6-dione (TPD) were designed and synthesized. The energy levels, light absorption, solubility and packing structure of random donors PBDTa-TPDb were found to vary substantially with the various D-A molar ratio. The devices based PBDTa-TPDb/P(NDI2HD-T) were fabricated to explore the synergistic effects of processing solvent and composition of D-A-type random polymers. The results show that nanoscale morphology, balanced miscibility/crystallinity of blend and photovoltaic properties could be rationally optimized by tuning the composition of random donors. As a result, as-cast all-PSC based optimal donor PBDT5-TPD4 achieves a best power conversion efficiency (PCE) of 8.20% processed from green solvent, which performs better than that based reference polymer (PCE: 6.41%). This efficiency is the highest value for all-PSCs from BDT-TPD-based donors. Moreover, the optimized devices exhibited relatively insensitive to the thickness of the active layer and good stability.

A series of bithiophene (2T)-based D-A₁-D-A₂ terpolymers with different A₂ moieties were prepared via direct arylation reaction. In these terpolymers, pyrrolo[3,4-c]pyrrole-1,4-dione (DPP) was selected as the first electron-accepting (A₁) moiety, 2,1,3-benzothiadiazole (BT) or fluorinated benzothiadiazole (FBT) or octyl-thieno[3,4-c]pyrrole-4,6-dione (TPD) or 2,1,3-benzoselendiazole (SeT) was selected as the second electron-accepting (A₂) moiety, while bithiophene with hexyl side chain was used as the electron-donating moiety. The UV-vis absorption, electrochemical properties, blend film morphology, and photovoltaic properties were studied to explore the effects of the A₂ moiety. It is shown that these terpolymer films exhibit broad absorption (350–1000 nm), full width at half-maximum of more than 265 nm and ordered molecular packing. Varying the A₂ moiety could affect the energy levels and blend film morphology leading to different polymer solar cell (PSC) performances of these (2T)-based D-A₁-D-A₂ terpolymers. As a result, the highest J_sc of 10.70 mA/cm² is achieved for Polymer 1 (P1) with BT as A₂ moiety, while the higher highest occupied molecular orbital (HOMO) level limits the open circuit voltage (V_oc) and leads to a power conversion efficiency (PCE) of 3.46%.

Tuning the structure of both polymer donors and acceptors, and development of novel matched donor/acceptor pairs are essential steps to enhance the power conversion efficiency (PCE) and stability of all-polymer solar cells (PSCs). Here, two weakly crystalline wide band-gap polymer donors PBDT(T)-HT-TPD and PBDT(ST)-HT-TPD with different side chains were synthesized by incorporating an alkyl-thiophene π-bridge, PBDT(T)TPD-based 2D-benzo[1,2-b:4,5-b]dithiophene (BDT) and thieno[3,4-c]pyrrole-4,6-dione (TPD) as reference donors. Three highly crystalline narrow-bandgap polymer acceptors P(NDI2OD-T), P(NDI2OD-Se) and P(NDI2HD-Se) sharing a similar backbone structure were also synthesized and studied. The all-PSCs were fabricated to investigate the synergetic effect of the alkyl-thiophene π-bridge and side chain modification. As a result, the PBDT(T)-HT-TPD/P(NDI2HD-Se) system is an optimal donor/acceptor combination due to its complementary light absorption and well-balanced miscibility/crystallinity, in which the highest power conversion efficiency (PCE) of 6.80% is achieved without extra-treatment. Meanwhile, the stability test of the devices shows that the incorporation of the alkyl-thiophene π-bridge can enhance thermal and storage stability. This work demonstrates that increasing the amorphous region of the donor to an appropriate degree provides an enhancement in the miscibility and morphology stability with highly crystalline acceptors, which will result in stable all-PSCs with high PCE.