Study of the processing pathway for cosolvent addition in active layer preparation of inverted organic solar cell

Investigation on processing pathway for co‐solvent addition in active layer preparation of an inverted organic solar cell indicated that the composite films cast out of simple marginal solvent (like cyclohexanone) addition in poly(3‐hexyl thiophene)‐6,6]‐phenyl C₆₁‐butyric acid methyl ester (P3HT‐PCBM) solution were not effectively crystallized. A comparison of one step direct marginal solvent addition to the P3HT‐PCBM solution with the modified two step process consisting of primary P3HT crystallization in first step by marginal solvent addition to a solution of only P3HT in good solvent (like ortho‐dichloro benzene) followed by mixing of PCBM solution revealed improvement in P3HT crystallization in the latter method. Grazing incidence X‐ray diffraction measurements supported favorable vertical concentration gradient in the P3HT‐PCBM composite film. This modification of active layer morphology with the two step individually mixed cyclohexanone addition into the active layer spin coating solution results in an improved power conversion efficiency of 3.39%, an improvement of more than 10% compared to the conventional one step blended co‐solvent addition method. POLYM. ENG. SCI., 55:1758–1766, 2015. © 2014 Society of Plastics Engineers