Highly efficient imide functionalized pyrrolo[3,4-c]pyrrole-1,3-dione-based random copolymer containing thieno[3,4-c]pyrrole-4,6-dione and benzodithiophene for simple structured polymer solar cells

Abstract

As an effort to improve the photovoltaic properties of a highly efficient large band gap (2.11 eV) alternating copolymer, P(BDT-TDPPDT), comprised of electron rich benzodithiophene (BDT) and novel electron accepting pyrrole-based imide functionalized 4,6-bis(thiophen-2-yl)-2,5-dioctylpyrrolo[3,4-c]pyrrole-1,3-dione (TDPPDT) derivatives, we incorporated a relatively strong electron accepting thiophene-based imide functionalized thieno[3,4-c]pyrrole-4,6-dione (TPD) unit in its main chain via random copolymerization between BDT, TDPPDT and TPD units to give polymer P1. The incorporation of a TPD unit resulted in significant improvement in the optoelectrical and photovoltaic properties. P1 exhibits lower optical band gap (1.91 eV) and a deeper lowest unoccupied molecular orbital (LUMO) energy level compared to those of P(BDT-TDPPDT). The hole mobility of P1 was 3.66 × 10⁻⁴ cm² V⁻¹ s⁻¹ and the PSC made with a simple device structure of ITO/PEDOT:PSS/P1:PC₇₀BM(1 : 2.25 wt%) + 3 vol%/Al gave a maximum power conversion efficiency (PCE) of 7.03% with high photovoltaic parameters, such as an open-circuit voltage (V_oc) of 0.87 V, a short-circuit current (J_sc) of 11.52 mA cm⁻² and a fill factor (FF) of 70%. Interestingly, P1-based PSCs exhibited a high incident photon to current efficiency (IPCE) of a maximum of 78% at 410 nm and a more than 70% response between 370–590 nm. The PCE achieved in this study is the highest value reported thus far among PSCs made with random copolymers.