A helicene-based semiconducting polymer for stable and efficient perovskite solar cells

The relentless pursuit of higher efficiencies in perovskite solar cells relies on the use of spiro-OMeTAD as a hole transport material, resulting in an impressive efficiency record of 25.7%. However, these high-efficiency cells have proven vulnerable to harsh heat conditions at 85°C. Here, we employed direct arylation polycondensation to efficiently synthesize a semiconducting polymer (p-O5H-E-POZ-E), the main chain of which consists of a strategic alternation of oxa[5]helicene, 3,4-ethylenedioxythiophene, phenoxazine, and 3,4-ethylenedioxythiophene. The air-doped composite of p-O5H-E-POZ-E and lithium bis(trifluoromethanesulfonyl)imide exhibits a room temperature conductivity of 75 μS cm⁻¹ and an exceptional glass-transition temperature of 187°C. Compared to spiro-OMeTAD, p-O5H-E-POZ-E demonstrates a comparable highest occupied molecular orbital energy level for efficient hole extraction while exhibiting enhanced elastic modulus and fracture strength and reduced water permeation in its composite film. Using p-O5H-E-POZ-E in the hole transport layer, we demonstrate perovskite solar cells with an average efficiency of 24.9% and thermostability at 85°C.