Vertical phase separation induced highly efficient pseudo-bilayer photoanodes for organic photoelectrochemical cells

Abstract

Replacing the alkyl side chains in 2,2′-((2Z,2′Z)-((4,4,9,9-tetrahexyl-4,9-dihydro-s-indaceno[1,2-b:5,6-b′]dithiophene-2,7-diyl)bis(methanylylidene))bis(3-oxo-2,3-dihydro-1H-indene-2,1-diylidene))dimalononitrile (IDIC) with polar diethylene glycol to form the hydrophilic acceptor 2,2′-((2Z,2′Z)-((4,4,9,9-tetrakis(2-(2-(2-methoxyethoxy)ethoxy)ethyl)-4,9-dihydro-s-indaceno[1,2-b:5,6-b′]dithiophene-2,7-diyl)bis(methaneylylidene))bis(3-oxo-2,3-dihydro-1H-indene-2,1-diylidene))dimalononitrile (IDIC-DEG) induced vertical phase separation (VPS) with the hydrophobic donor poly[(2,5-bis(2-hexyldecyloxy)phenylene)-alt-(5,6-difluoro-4,7-di(thiophen-2-yl)benzo[c]-thiadiazole)] (PPDT2FBT) due to surface energy differences, leading to IDIC-DEG accumulation near the ZnO bottom layer. The photoelectrochemical properties of PPDT2FBT : IDIC and PPDT2FBT : IDIC-DEG blends were studied and compared. The VPS in PPDT2FBT : IDIC-DEG optimized charge extraction in photoelectrochemical cells and stable ZnO/IDIC-DEG interface prevented delamination in water. The DEG side chain also increased the dielectric constant and water uptake, reducing charge transfer resistance, resulting in significantly improved photocurrent and photoanode stability.