Semi-crystalline photovoltaic polymers with efficiency exceeding 9% in a similar to 300 nm thick conventional single-cell device

Abstract

We report a series of semi-crystalline, low band gap (LBG) polymers and demonstrate the fabrication of highly efficient polymer solar cells (PSCs) in a thick single-cell architecture. The devices achieve a power conversion efficiency (PCE) of over 7% without any post-treatment (annealing, solvent additive, etc.) and outstanding long-term thermal stability for 200 h at 130 degrees C. These excellent characteristics are closely related to the molecular structures where intra-and/or intermolecular noncovalent hydrogen bonds and dipole-dipole interactions assure strong interchain interactions without losing solution processability. The semi-crystalline polymers form a well-distributed nano-fibrillar networked morphology with PC70BM with balanced hole and electron mobilities (a h/e mobility ratio of 1-2) and tight interchain packing (a pi-pi stacking distance of 3.57-3.59 A) in the blend films. Furthermore, the device optimization with a processing additive and methanol treatment improves efficiencies up to 9.39% in a similar to 300 nm thick conventional single-cell device structure. The thick active layer in the PPDT2FBT: PC70BM device attenuates incident light almost completely without damage in the fill factor (0.71-0.73), showing a high short-circuit current density of 15.7-16.3 mA cm(-2). Notably, PPDT2FBT showed negligible changes in the carrier mobility even at similar to 1 mm film thickness.