Altering the thermodynamics of phase separation in inverted bulk-heterojunction organic solar cells

The incorporation of fractional amounts of nonvolatile additives in the photoactive layer of P3HT and PCMB was reported. Inverted bulk-hetrerojunction solar cells were fabricated on pattered ITO glass substrates that were cleaned in an ultrasonic bath using acetone, isopropyl alcohol, and de-ionized water. A convenient way of generating an interpenetrating morphology is to deposit a blend consisting of an electron donor and an acceptor from a common solvent. The incorporation of fractional amounts of nonvolatile additives within the photoactive layer can improve inverted bulk-heterojunction organic solar cell device efficiencies by two-fold. These additives selectively partition into P3HT, effectively enhancing phase separation between the electron donor and acceptor phases. The extent of phase separation was influenced by the hydrophobicity of the additives, with the most hydrophobic ligands increasing χ the most.