Enhanced Photoresponse in Solid-State Excitonic Solar Cells via Resonant Energy Transfer and Cascaded Charge Transfer from a Secondary Absorber

We present a spiro linked molecule 2 2' 7 7' tetrakis(3 hexyl 5 (7 (4 hexylthlophen 2 yl)benzo[c][1 2 5]thiadiazol 4 4 yl)thiophen 2 yl) 9 9' spirobifluorene which acts as a secondary absorber in solid state excitonic solar cells Blending with a hole transpoting matenal 2 2'7 7'-tetrakis(N N di-p-methoxyphenyl amine) 9 9' spirobifluorene and used in conjunction with a near infrared dye (termed TTI) results in an extended spectral response which yields a notable increase in short circuit current and power conversion efficiency This enhancement is due to both exciton energy transfer and also nanoscale charge generation in the blend via the formation of an excited sate spiro complex with charge transfer character