Modification of Terminated Group with the Optimal Composition of a Phosphonate Side Chain for Effectiveness in Inverted Polymer Solar Cells

Abstract

Isoindigo-based copolymers have high power conversion efficiency (PCE) of up to 5 %. Given these results, both IIGDT copolymers and isoindigo-based (IIG) copolymers are promising organic opto-electric active materials. Component ratio control with phosphonate side-chain IIG and normal alkyl side-chain IIG with bithiophene copolymers showing improved of PCE and unique film orientations. The resulting polymers show trends in changes of optical properties and electrochemical energy level. These four polymers are applicable to inverted polymer solar cells, which has maximum PCE 5.95%, a 19% improvement over the normal alkyl side-chain polymer. Furthermore, the phosphonate side-chain effect exhibits film crystallinity from grazing-incidence wide-angle x-ray scattering (GIWAXS), enhancing the edge-on crystalline orientation with increased of the phosphonate ratio, while inserting additive into the polymer:PC71BM blend system reduced the intensity of out-of-plane π-π stacking.