Control of crystallinity of naphthalene diimide-based terpolymers and their effects on performance of all-polymer solar cells

Abstract

A new series of n-type D-A terpolymers (P(NDI2HD-T-S)) was synthesized from an electron-deficient naphthalene diimide (NDI)-based unit in conjugation with two electron-rich thiophene (T) and selenophene (S) units and their performances as electron acceptors in all-polymer solar cells (all-PSCs) were compared. The crystallinity of the P(NDI2HD-T-S) terpolymers can be controlled systematically by tuning the T/S molar ratios (T/S= 100/0, 80/20, 50/50, 20/80, and 0/100) in the polymer backbone

an increase in S content induced a significant enhancement in the crystallinity of the terpolymers. Thus, incorporation of more S unit enhanced the structural ordering of the terpolymers and the electron mobility in the all-PSCs. All-PSCs based on P(NDI2HD-T-S) terpolymer acceptor and PTB7 polymer donor exhibited an increasing trend of the power conversion efficiency from 2.50 to 3.60 % for higher S content, which was mainly attributed to the enhanced short circuit current. To understand the effects of the T/S compositions on the photovoltaic performances, we investigated their influence on the optical, electrical, and structural properties of the n-type D-A terpolymers.