Efficient and Stable Colloidal Quantum Dot Solar Cells with a Green-Solvent Hole-Transport Layer

Next-generation solution-processed solar cells will hopefully be processed using green solvents, and will unite high performance with operating stability. Colloidal quantum dot/polymer hybrid solar cells are of interest for their harvest of the visible as well as the near infrared; however, today's best polymer hole-transporting layers (HTLs) rely on processing using hazardous solvents such as chlorobenzene. This stems from the strong polymer–polymer attraction in polymeric p-type materials, which accounts for their limited solubility. Here, a new random polymeric HTL (asy-ranPBTBDT) is reported that is soluble in green solvents such as 2-methylanisole without compromising ultimate device power conversion efficiency. The new polymer structure induces a strong π–π stacking face-on orientation and less lateral grain growth compared to control asy-PBTBDT, leading to reduced charge recombination and improved device stability. The resulting device exhibits a power conversion efficiency (PCE) of 13.2% and retains 89% of its initial efficiency after 120 h of continuous device operation at the maximum power point, compared to a PCE of 11.4% and 71% degradation for control devices.