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

Abstract

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 cm2 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.