From Straw to Device Interface: Carboxymethyl‐Cellulose‐Based Modified Interlayer for Enhanced Power Conversion Efficiency of Organic Solar Cells

Abstract Advanced interface materials made from petrochemical resources have been extensively investigated for organic solar cells (OSCs) over the past decades. These interface materials have demonstrated excellent performances in OSC devices. However, the limited resources, high‐cost, and non‐ecofriendly nature of petrochemical‐based interface materials restrict their commercial applications. Here, a facile and effective approach to prepare cellulose and its derivatives as a cathode interface layer for OSCs with enhanced performance from rice straw of agroforestry residues is demonstrated. By employing this carboxymethyl cellulose sodium (CMC) into OSCs, a highly efficient inverted OSC is constructed, and a power conversion efficiency (PCE) of 12.01% is realized using poly[(2,6‐(4,8‐bis(5‐(2‐ethyl‐hexyl)‐thiophen‐2‐yl)‐benzo[1,2‐b:4,5‐b′] dithiophene))‐ alt ‐(5,5‐(1′,3′‐di‐2‐thienyl‐5′,7‐bis(2‐ethylhexyl)benzo[1′,2′‐c: 4′,5′‐c′]dithiophene‐4,8‐dione): 3,9‐bis(2‐methylene‐((3‐(1, 1‐dicyanomethylene)‐6/7‐methyl)‐indanone))‐5,5,11,11‐tetrakis(4‐hexylphenyl)‐dithieno[2,3‐d: 2′,3′‐d′]‐s‐indaceno[1,2‐b: 5, 6‐b′]dithiophene as the active layer, which shows over 9.4% improvement in PCE compared to that of a device without the CMC layer (PCE = 10.98%), especially the enhancement in short‐circuit current. The improved current densities and PCEs are attributed to the reduced work function, enhanced absorption, and improved interfacial contact by using CMC and ZnO as co‐interface. This approach of fabricating interface materials from biorenewable sources for OSCs is simple, scalable, and cost‐effective, representing a promising direction for the development of smart interface and green electronics.