Optical and electrical properties of a squaraine dye in photovoltaic cells

2,4-Bis[4-(N,N-diisobutylamino)-2,6-dihydroxyphenyl] squaraine (SQ) was employed as a donor material in organic photovoltaic cells based on planar heterojunctions. We studied optical properties of SQ films, and discussed its photovoltaic performance via numerical fitting and simulation on the photovoltaic cells. Exciton diffusion length (LD) in SQ films (4.5 nm) derived from optical simulation should be the major limitation to efficiency, consistent with external quantum efficiency data. Thermal treatment improved efficiency, which can be ascribed to reduced saturation current of the photovoltaic cells. As a result, a power conversion efficiency of 4.1% was achieved.