Over the past fi ve years, a rapid progress in organometal-halide perovskite solar cells has greatly infl uenced emerging solar energy science and technology. In perovksite solar cells, the overlying hole transporting material (HTM) is critical for achieving high power conversion effi ciencies (PCEs) and for protecting the air-sensitive perovskite active layer. This study reports the synthesis and implementation of a new polymeric HTM series based on semiconducting 4,8-dithien-2-yl-benzo[1,2-d ;4,5-d ′]bistriazolealt -benzo[1,2-b :4,5b ′]dithiophenes (pBBTa-BDTs), yielding high PCEs and environmentally-stable perovskite cells. These intrinsic (dopant-free) HTMs achieve a stabilized PCE of 12.3% in simple planar heterojunction cells-the highest value to date for a polymeric intrinsic HTM. This high performance is attributed to effi cient hole extraction/collection (the most effi cient pBBTa-BDT is highly ordered and orients π-face-down on the perovskite surface) and balanced electron/ hole transport. The smooth, conformal polymer coatings suppress aerobic perovskite fi lm degradation, signifi cantly enhancing the solar cell 85 °C/65% RH PCE stability versus typical molecular HTMs.

We report a small-molecule electron-acceptor based on 2-vinyl-4,5dicyanoimidazole [VinazeneÔ] for use in solution processed organic solar cells. The material has a favourably located LUMO level of À3.6 eV and absorbs strongly in the visible spectrum up to 520 nmattractive properties compared to the widely used acceptor (6,6)phenyl-C 60 -butyric acid methyl ester (PCBM). The Vinazene derivative was blended with a poly(2,7-carbazole) donor-chosen for its complementary absorption range and comparatively high-lying HOMO level of À5.6 eV-and incorporated into bulk heterojunction devices. The influence of the donor/acceptor composition and annealing temperature on device performance were then investigated. The best performing devices exhibited reasonable power conversion efficiencies of 0.75% and open-circuit voltages of more than 1.3 V, substantially higher than previously reported devices using small molecule acceptors.