Beyond Metal Oxides: Introducing Low-Temperature Solution-Processed Ultrathin Layered Double Hydroxide Nanosheets into Polymer Solar Cells Toward Improved Electron Transport

Metal oxides such as zinc oxide (ZnO) have been commonly used as the cathode interfacial layer (CIL) of bulk heterojunction inverted polymer solar cells (BHJ-iPSCs), for which a high-temperature annealing treatment is usually required to improve their CIL performance. Layered double hydroxides (LDHs) are a class of inorganic two-dimensional (2D) nanomaterials composed of positively charged brucite-like layers intercalated with charge-balancing anions and water molecules, showing potential applications in catalysis, adsorption, electrochemical energy storage and conversion, etc., but have never been applied in PSCs. Herein, for the first time LDH nanosheets are applied in BHJ-iPSC devices as a novel CIL substituting the commonly used ZnO, affording an obvious efficiency enhancement relative to ZnO-based device. Ultrathin Mg_xAl-NO₃-LDH nanosheets are prepared by ultrasonication-assisted liquid exfoliation of bulk Mg_xAl-NO₃-LDHs prepared via a co-precipitation method, and deposited onto an ITO substrate as a CIL by a low-temperature solution-processed technique. Based on Mg_xAl-NO₃-LDH CIL, BHJ-iPSC devices with the poly(4,8-bis-alkyloxybenzo(l,2-b:4,5-b′)-dithiophene-2,6-diylalt-(alkylthieno(3,4-b) thiophene-2-carboxylate)-2,6-diyl):[6,6]-phenyl C71-butyric acid methyl ester (PBDTTT-C:PC₇₁BM) photoactive layer exhibits an improvement of power conversion efficiency relative to those based on ZnO CIL. This is primarily originated from the increase of fill factor due to the improved interfacial contact between the ITO and active layer, facilitating the interfacial electron transport.