As the hole transport layer (HTL) for perovskite solar cells (PSCs), poly(3‐hexylthiophene) (P3HT) has been attracting great interest due to its low‐cost, thermal stability, oxygen impermeability, and strong hydrophobicity. In this work, a new doping strategy is developed for P3HT as the HTL in triple‐cation/double‐halide ((FA_1−x−yMA_xCs_y)Pb(I_1−xBr_x)₃) mesoscopic PSCs. Photovoltaic performance and stability of solar cells show remarkable enhancement using a composition of three dopants Li‐TFSI, TBP, and Co(III)‐TFSI reaching power conversion efficiencies of 19.25% on 0.1 cm² active area, 16.29% on 1 cm² active area, and 13.3% on a 43 cm² active area module without using any additional absorber layer or any interlayer at the PSK/P3HT interface. The results illustrate the positive effect of a cobalt dopant on the band structure of perovskite/P3HT interfaces leading to improved hole extraction and a decrease of trap‐assisted recombination. Non‐encapsulated large area devices show promising air stability through keeping more than 80% of initial efficiency after 1500 h in atmospheric conditions (relative humidity ≈ 60%, r.t.), whereas encapsulated devices show more than >500 h at 85 °C thermal stability (>80%) and 100 h stability against continuous light soaking (>90%). The boosted efficiency and the improved stability make P3HT a good candidate for low‐cost large‐scale PSCs.

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).

In the present work we used some crystallization trends which could be classified as a Crystal Engineering (CE) approach, for deposition of a pure cubic-phase thin film of CH₃NH₃PbI₃ (MAPbI₃) on the surface of a mesoporous TiO₂ layer.