Flawless Photocurrent Extraction from a Thick Polymer Bulk Heterojunction

Abstract

We report a dialkoxyphenylene-difluorobenzothiadiazole based conjugated polymer (PPDT2FBT) which closely tracks theoretical photocurrent production while maintaining a high fill factor in remarkably thick films. The unique behavior of thick PPDT2FBT films arises from physical properties including high vertical carrier mobility, an isotropic morphology with strong, vertical π-π stacking and a suitable energy band structure. These physical characteristics allow efficient photocurrent extraction, internal quantum efficiencies near 100% and power conversion efficiencies over 9% from exceptionally thick active layers in both conventional and inverted architectures. The ability of PPDT2FBT to function efficiently in thick cells allows devices to fully attenuate incident sunlight while providing a pathway to defect-free film processing over large areas, constituting a major advancement towards commercially viable organic solar cells.