Nonhalogenated Solvent‐Processed Thick‐Film Ternary Nonfullerene Organic Solar Cells with Power Conversion Efficiency >13% Enabled by a New Wide‐Bandgap Polymer

Abstract

Although several donor polymers have been synthesized for use in nonfullerene organic solar cells (NFOSCs), the number of efficient π‐conjugated donor polymers compatible with nonhalogenated solvent‐processed thick active layer NFOSCs is limited. Two wide‐bandgap π‐conjugated donor polymers functionalized with a siloxane side chain, P1 (chlorine‐free) and P2 (chlorinated), are designed and synthesized. The siloxane‐functionalized side chains and/or Cl π‐conjugated donor polymers increase the absorption coefficients, reduce the energy losses, increase the charge‐carrier mobility, and suppress the bimolecular recombination, which are beneficial to achieve high‐performance thick‐film ternary NFOSCs. Toluene‐processed devices based on P2:IT‐4F:BTP‐4Cl, and P2:IT‐4F:BTP‐4F exhibit high power conversion efficiencies (PCEs) of 13.25% and 11.02% with fill factors (FFs) of 70.03% and 71.60%, respectively. A P2:IT‐4F binary NFOSC exhibits a PCE of 10.38% with an FF of 69.78%, lower than that of the ternary NFOSC. The ternary device PCE of 13.25% is achieved using a 300 nm‐thick active layer, indicating that the siloxane‐functionalized side‐chain π‐conjugated polymer easily controls the bulk heterojunction blend film thickness of the NFOSC. The findings may potentially aid the development of nonhalogenated solvent‐processed thick‐film ternary NFOSCs that can satisfy future production requirements.

All-Polymer Solar Cells Approaching 12% Efficiency with a New π-Conjugated Polymer Donor Enabled by a Nonhalogenated Solvent Process

“…As shown in the images, the WCAs of optimized films exhibited large differences. Moreover, the 1-PN-TA-based device exhibited high γ s due to good miscibility achieved by low interfacial tension and efficient charge transport between the active layer and the electrode . Thus, optimized active layer morphology and reduced recombination loss can enhance the V oc of all-PSCs. , In addition, we confirmed the molecular orientation and arrangement of the polymer backbone and side chains in the edge-on orientation (low γ s ).…”

“…Moreover, the 1-PN-TA-based device exhibited high γ s due to good miscibility achieved by low interfacial tension and efficient charge transport between the active layer and the electrode . Thus, optimized active layer morphology and reduced recombination loss can enhance the V oc of all-PSCs. , In addition, we confirmed the molecular orientation and arrangement of the polymer backbone and side chains in the edge-on orientation (low γ s ). The higher γ s leads to the face-on orientation. , Therefore, we further investigated the morphologies of these optimized all-PSCs to discern the cause of the observed PCE improvements.…”

“…Blend wetting properties and phase separation of active layers contributed directly to the surface energies (γ s ). − The water contact angles (WCAs) of 1-PN-TA, TA, and pristine optimized films were 91.96°, 95.80°, and 98.01°, respectively (Figure b). The γ s values of 1-PN-TA and TA films were higher than that of the pristine film (44.9 and 44.3 mJ m –2 vs 41.2 mJ m –2 ) (Table S15).…”

“…The γ s values of 1-PN-TA and TA films were higher than that of the pristine film (44.9 and 44.3 mJ m –2 vs 41.2 mJ m –2 ) (Table S15). The Owens–Wendt (O–W) geometric equation is commonly used to estimate the γ s values of polymers , and thus was used in the present study. As shown in the images, the WCAs of optimized films exhibited large differences.…”

“…Grazing incidence X-ray diffraction (GIXRD) measurements were obtained using a synchrotron X-ray beam to investigate molecular packings and orientations of the thick-film all-PSCs. ,, As seen in Figure c, the GIXRD pattern of Nap-SiBTz:N2200 films showed a broad peak in the high q region in the out-of-plane direction, while several reflections appeared along the q xy direction, as indicated in the pristine device, showing a “face-on” structure of π planes oriented parallel to the substrate. We found that TA and 1-PN-TA films exhibited nearly the same patterns as the pristine film, meaning that 1-PN did not change the molecular packing structure of the pristine film.…”