ИСТИНА

A series of (BDD-X)n conjugated polymers comprised of 5,7-bis(2-ethylhexyl)benzo[1,2- c:4,5-c′]dithiophene-4,8-dione (BDD) and X = B (P1), X = TBT (P2) and X = TBTBT (P3), where T = thiophene, B = benzo[c][1,2,5]thiadiazole, have been synthesized and applied as dopantfree hole-transport layer materials in perovskite solar cells (PSCs). We explored the effect of the molecular structure of the block X on the optical and electronic properties of the polymers,nanoscale morphology of their films, and the impact of all these parameters on the performance of the polymers in PSCs. As a result, using the polymer P1 with the simplest molecular architecture provided the power conversion efficiency (PCE) of 20.1% in solar cells thus outperforming the devices assembled with more sophisticated polymers P2-P3 or the reference poly(triarylamine)-based hole-transport materials. The enhanced device performance is attributed to a better HOMO alignment of Р1 with respect to the perovskite valence band, low concentration of defects and suppressed carrier recombination at P1/perovskite interface and, most importantly, highly uniform film structure as revealed by atomic force microscopy and infrared scattering near-field optical microscopy (IR s-SNOM) techniques. The supramolecular interactions of the building blocks of polymers P1-P3 with the perovskite films resulting in the passivation of surface defects were further studied by density functional theory calculations.