Green‐Solvent‐Processed 17% Efficient Polymer Solar Cell Achieved Synergistically by Aligning Energy Levels and Improving Morphology with the Quaternary Strategy

Abstract

Low and unbalanced charge mobilities result in low short‐circuit current density (JSC) and small fill factor (FF), which greatly limits the power conversion efficiencies (PCEs) of polymer solar cells (PSCs) processed with green solvents. Herein, a unique quaternary material system (PM6:BTP‐BO‐4F:BTP:PhI‐Se) is reported, which uses an upshifted highest occupied molecular orbital (HOMO) acceptor guest (BTP) and a deep‐HOMO, ultra‐wide bandgap polymer donor guest (PhI‐Se) as quaternary strategy to align energy levels and improve morphology, leading to open‐circuit voltage (VOC) (from 0.812 to 0.851 V), FF (from 66.1% to 76.7%), and JSC (from 24.4 to 26.1 mA cm−2) increased simultaneously, hence obtaining PCEs of 17.0% processed with toluene. When processed with chlorobenzene (CB), 18.2% efficiency is obtained. Adding BTP and PhI‐Se as the third component increases hole and electron mobilities, respectively, going from 1.32/0.63 × 10−4 cm2 V−1 s−1 for the host binary to 1.56/2.56 and 2.26/2.86 × 10−4 cm2 V−1 s−1 for the BTP and PhI‐Se ternary. With both adding, the values shift to 3.69/3.20 × 10−4 cm2 V−1 s−1 for the quaternary blends. The crystalline coherence length (CCL) increases from 18.8 nm to 20.2 nm and 23.6 nm, respectively, for the two ternaries, and then 25.7 nm for the quaternary blend.