Room-Temperature Solution-Processed n-Doped Zirconium Oxide Cathode Buffer Layer for Efficient and Stable Organic and Hybrid Perovskite Solar Cells

In this study, we present a simple and effective method to improve the performance and stability of organic and hybrid perovskite solar cells by the incorporation of solution-processed cetyltrimethylammonium bromide (CTAB)-doped zirconium oxide (ZrO_x) as cathode buffer layer (CBL). This novel n-doped ZrO_x CBL possesses several remarkable features, including ease of fabrication without the need for thermal annealing or any other post-treatment, reasonable electrical conductivity (2.9 × 10^-5 S cm^-1), good ambient stability, effective work function modulation of Ag electrode, relative weak thickness-dependent performance property, and wide applicability in a variety of active layers. Compared with ZrO_x CBL without CTAB dopant, CTAB-doped ZrO_x can significantly improve the power conversion efficiency (PCE) from 0.57% to 2.48% in organic solar cells based on diketopyrrolopyrrole-thiophene-bezothiadazole low-bandgap polymer (PDPP-TBT):[6,6]-phenyl-C₇₁-butyric acid methyl ester (PC₇₁BM) blend. With this n-doped ZrO_x CBL, organic solar cells based on polythieno(3,4-b)-thiophene-alt-benzodithiophene (PTB7):PC₇₁BM blend deliver a record high PCE of 9.3%. The effectiveness of this novel CBL also extends to perovskite solar cells, and a high PCE up to 15.9% is demonstrated, which is superior to those of the devices with undoped ZrO_x and state-of-the-art CBL zinc oxide nanoparticle film. In addition, this approach is applicable to the development of high-performance semitransparent solar cells. More significantly, the long-term ambient stability of the resulting devices can be secured without the need of rigorous encapsulation.