Interfacial modification to improve inverted polymer solar cells
We report improved device performance of poly(3-hexylthiophene) (P3HT)\nand [6,6]phenyl C butyric acid methyl ester (PCBM)-based inverted\nbulk-heterojunction (BHJ) solar cells through the modified interface\nof the TiO/BHJ with a series of carboxylic acid functionalized self-assembled\nmonolayers (SAMs). The SAMs reduce the series resistance and improve\nthe shunt resistance of the cell leading to increased fill factor\nand photocurrent density. Different aspects of device improvement\ncan be affected depending on the nature of the SAMs. Modification\nwith a C-SAM shows the largest enhancement leading to a 35% improvement\n( = 3.78%) over unmodified inverted devices ( = 2.80%). This SAM\nserves multiple functions to affect the photoinduced charge transfer\nat the interface to reduce the recombination of charges, passivation\nof inorganic surface trap states, improve the exciton dissociation\nefficiency at the polymer/TiO interface as well as a template to\ninfluence the overlayer BHJ distribution of phases, morphology and\ncrystallinity leading to better charge selectivity and improved solar\ncell performance.