Toward Scalable PbS Quantum Dot Solar Cells Using a Tailored Polymeric Hole Conductor

Colloidal quantum dot (CQD) solar cells processed from pre-exchanged lead sulfide (PbS) inks have received great attention in the development of scalable and stable photovoltaic devices. However, the current hole-transporting material (HTM) 1,2-ethanedithiol-treated PbS (PbS-EDT) CQDs have several drawbacks in terms of commercialization, including the need for oxidation and multilayer fabrication. Conjugated polymers are an alternative HTM with adjustable properties. Here we propose a series of conjugated polymers (PBDB-T, PBDB-T(Si), PBDB-T(S), PBDB-T(F)) for PbS CQD solar cells as HTMs. Through polymer side-chain engineering, we optimize the model polymer PBDB-T to tune the energy levels, increase hole mobility, improve solid-state ordering, and increase free carrier density. CQD solar cells based on modified polymer PBDBT-(F) exhibit a best power conversion efficiency (PCE) of 11.2%, which outperforms the devices based on conventional PbS-EDT HTM (10.6%) and is currently the highest PCE for PbS solar cells based on organic HTMs.