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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.

Hole transport materials (HTMs) play essential roles in achieving high photovoltaic performance and long‐term stability in the n–i–p structure of perovskite solar cell (PSC) devices. Recently, dopant‐free polymeric materials as HTMs in PSCs have attracted considerable attention owing to high carrier mobility and excellent hydrophobicity. However, achieving similar efficiencies to those of doped small molecule HTMs such as Spiro‐OMeTAD is a big challenge. Herein, a thienothiophene π‐bridge is selected as a stabilizer and energy level regulator incorporated into a donor–acceptor‐type HTM to synthesize a new polymer, Nap‐SiBTA. The incorporation of the thienothiophene group improves the thermal stability and favors the high planarity and face‐on orientation, promoting high charge carrier mobility and tunable optical band gap. Finally, the dopant‐free polymer Nap‐SiBTA‐based PSC achieves an excellent power conversion efficiency (PCE) of 23.07% with a high fill factor of 80.85%. To the best of the authors’ knowledge, this is one of the best efficiencies in dopant‐free HTM PSCs. Moreover, the unencapsulated device retains 93% of its initial PCE after 1000 h owing to the excellent hydrophobicity of Nap‐SiBTA. This work provides a general and practical method to design dopant‐free HTMs for the high efficiency and long‐term stability of PSCs.

High efficiency and nonhalogenated solvent processing are important issues for commercial application of all-polymer solar cells (all-PSCs). In this regard, we increased the photovoltaic performance of all-PSCs to a benchmark power conversion efficiency (PCE) of 11.66% by manipulating the pre-aggregation of a new π-conjugated polymer donor (Nap-SiBTz) using toluene as a solvent. This use of Nap-SiBTz enhanced the absorption coefficient (λmax = 9.30 × 104 cm–1), increased charge carrier mobility, suppressed trap-assisted recombination, improved bulk heterojunction morphology, and resulted in high PCEs of all-PSCs with an active layer thickness of 200 nm. To overcome severe charge recombination and energy losses, a 1-phenylnapthalene additive was used to achieve a well-ordered microstructure and molecular packing that inherently improved the device performances. The resulting encapsulation-free devices exhibited good ambient and thermal stabilities. The results of this study augur well for the future of the roll-to-roll production of all-PSCs.

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