Wide-Band-Gap Phthalimide-Based D-π-A Polymers for Nonfullerene Organic Solar Cells: The Effect of Conjugated π-Bridge from Thiophene to Thieno[3,2-b]thiophene

Abstract

Conjugated polymers with D-π-A backbone structures have been intensively investigated and have largely promoted the rapid progress of organic solar cells (OSCs). However, as one of the simplest electron-accepting (A) units, phthalimide (PhI) only attracts less attention to construct promising D-π-A photovoltaic polymers in the OSC community. Thus, the correlations among the chemical structure, optoelectronic properties, and photovoltaic performance need to be systematically investigated. Here, we combined the PhI moiety with the electron-donating (D) unit benzodithiophene (BDT) to synthesize two D-π-A copolymers PE80 and PE81, where the π-bridge corresponds to the thiophene (T) and thieno[3,2-b]thiophene (TT), respectively. When blended with a low-band-gap (Eg = 1.33 eV) nonfullerene acceptor Y6, PE81 achieved a power conversion efficiency (PCE) of 10.21% with an open-circuit voltage (VOC) of 0.90 V, which are much higher than those of the PE80:Y6 device (PCE = 4.11% and VOC = 0.88 V). Our results indicate that PhI is also a promising electron-deficient unit to construct photovoltaic polymers and using a TT π-bridge is a simple strategy to improve the photovoltaic performance of D-π-A polymers.