Tetrapropyl-tetraphenyl-diindenoperylene Derivative As a Green Absorber for High-Voltage Stable Organic Solar Cells

We present small molecule organic solar cells (SMOSC) based on flat heterojunctions (FHJ) of the alternative green donor 2,3,10,11-tetrapropyl-1,4,9,12-tetraphenyl-diindeno[ 1,2,3-cd: 1`, 2`, 3`-lm]perylene (P4-Ph4-DIP) and the fullerene C-60. P4-Ph4-DIP absorbs in the green spectral range and thus fills the spectral gap that standard absorber materials (zinc or copper phthalocyanine for red and C-60 for blue absorption) leave, thus allowing broad coverage of the sun spectrum, which is of major interest for tandem devices. The materials properties of P4-Ph4-DIP are studied, and SMOSC are characterized by current voltage, external quantum efficiency, and aging measurements. The solar cells display very high fill factors FF > 76% and open circuit voltages V-OC of close to 1 V. Mismatch-corrected efficiencies of up to 1.9% are obtained. Aging measurements show that C-60 in conjunction with P4-Ph4-DIP yields extremely stable devices. We observe approximate to 88% of the initial efficiency after 2500 h illumination at 999 mW/cm(2) illumination intensity, with no observable change in short-circuit current density. Furthermore, we also show that a systematic variation of donor thickness in FHJ can be combined with transfer matrix formalism-based optical simulations and the continuity equation for excitons to reliably determine the exciton diffusion length L-D. A value of 9 +/- 1 nm is found for P4-Ph4-DIP.