Organic solar cells based on a novel infrared absorbing aza-bodipy dye

For high efficiencies, organic solar cells have to harvest a large part of the solar spectrum. However, in particular for small molecule based cells, efficient infrared absorbers are still rare. We investigate here two aza-bodipy dyes which have promising properties. Upon benzannulation of the pyrrole of difluoro-bora-1,3,5,7-tetraphenyl-aza-dipyrromethene (Ph4-bodipy), the thin film absorption maximum is shifted by about 70–773 nm compared to the non-annulated molecule. The thin film properties of both materials are investigated and vacuum-processed solar cells using a mip-architecture (metal intrinsic p-doped) are compared. With the new benzannulated difluoro-bora-bis-(1-phenyl-indoyl)-azamethine (Ph2-benz-bodipy) as donor material, these planar heterojunction solar cells show an open-circuit voltage of 0.65 V, a fill factor of 65%, and an external quantum efficiency extending up to 860 nm. The mismatch corrected power conversion efficiency reaches 1.1%.

► We present the new class of aza-bodipy used in OSC for the first time.
► Benzannulation of phenyl rings leads to redshift of the absorption into the IR.
► Solar cells show a external quantum efficiency up to 860 nm.
► In combination with C60, a high FF of 65% and a high VOC of 0.65 V is reached.