Fluorination of Star‐Shaped Cyclopenta[2,1‐b;3,4‐b′]dithiophene Derivatives and Its Application as Hole‐Transporting Materials in Scalable Perovskite Solar Cell Fabrication by Bar Coating

In this study, three novel star‐shaped small molecules HYC‐oF , HYC‐mF , and HYC‐H are designed and synthesized and are applied in perovskite solar cells (PSCs) as efficient hole‐transporting materials (HTMs). Compared with non‐fluorinated HYC‐H , F‐substituted analogs HYC‐oF and HYC‐mF exhibited enhanced hole mobility, suitable energy level alignment, improved interfacial contact and hole extraction/transport capability, better passivation effect, as well as increased hydrophobicity. PSC fabrication by spin‐coating this series of HYC‐oF , HYC‐mF , and HYC‐H molecules on a bar‐coated perovskite layer yielded PCEs values of 19.64%, 18.38%, and 16.98%, respectively. In order to realize a fully scalable PSC preparation process, sequential coating of HYC‐oF layer on perovskite layer all by thermal‐assisted bar‐coating (TABC) method was carried out on 10 × 10 cm 2 area. The TABC‐based HYC‐oF layer had a compact and uniform morphology with full surface coverage on the TABC‐based perovskite film. Under optimized condition, the PSCs fabricated from such film exhibited a PCE of 18.49% as compared with a lower power conversion efficiency (PCE) of 17.51% from the reference cell using TABC‐based spiro‐OMeTAD. This work demonstrates the potential of fluorinated star‐shaped cyclopenta[2,1‐b;3,4‐b′]dithiophene (CPDT)‐based molecule as HTM for achieving efficient PSC in both small and large scale.