Impact of P3HT Regioregularity and Molecular Weight on the Efficiency and Stability of Perovskite Solar Cells

The commercialization of perovskite solar cells (PSCs) has seen an important limitation in the instability that afflicts the hole-transporting layer (HTL), namely, spiro- OMeTAD, used in high-efficiency devices. The latter is, in turn, relatively expensive, undermining the sustainability of the device. Its replacement with polymeric scaffolds, such as poly(3- hexylthiophene) (P3HT), will solve these issues. In this work, we adopted various sustainable synthetic methods to obtain four different homemade P3HTs with different molecular weights (MWs) and regioregularities (RRs), leading to different structural properties. They are implemented as HTLs in PSCs, and the effect of their properties on the efficiency and thermal stability of devices is thoroughly discussed. The highest efficiency is obtained with the highest MW and low-RR polymer (17.6%) owing to the more sustainable approach, but a very promising value is also reached with a lower-MW but fully regioregular polymer (15%). Finally, large-area devices with an efficiency of 16.7%, fabricated with a high-MW P3HT, show more than 1000 h (T80 = 1108 h) of stability under accelerated thermal stress tests (85 °C) out of glovebox while keeping over 85% of the initial efficiency of an unencapsulated device after more than 3000 min under continuous light soaking (AM 1.5G).