Synthesis of Sulfur/Nitrogen‐Enriched Polyimide and Interlayer Application for Inverted Polymer:Nonfullerene Solar Cells

Herein, it is reported that sulfur/nitrogen‐enriched polyimide can act as a stable interlayer for inverted‐type polymer:nonfullerene solar cells because it improves the power conversion efficiency (PCE) and stability of the devices. The sulfur/nitrogen‐enriched polyimide (E‐PI) interlayers are prepared on the zinc oxide layers via the thermal imidization of corresponding films of soluble precursor polymer, poly( N ‐(2‐((carboxymethyl)(2‐((5‴‐methyl‐[2,2″:5″,2″:5″,2‴‐quaterthiophen]‐5‐yl)amino)‐2‐oxoethyl)amino)ethyl)‐ N ‐(2‐(methylamino)‐2‐oxoethyl)glycine acid), which is synthesized from ethylenediaminetetraacetic dianhydride and 5,5‴‐diamino‐2,2″:5″,2″:5″,2‴‐quaterthiophene. The E‐PI films exhibit high glass transition temperature (≈204 °C) and broad optical absorption up to ≈1000 nm (absorption edge). Results show that the average PCE of polymer:nonfullerene solar cells is increased from 10.86% to 11.6% at the E‐PI thickness of 3 nm. In particular, the stability of polymer:nonfullerene solar cells is clearly improved by inserting the 3 nm‐thick E‐PI interlayers.