Novel core-modulated naphthalenediimides with CN-TFPA as electron transport layer for inverted perovskite solar cells

Herein we report the design and synthesis of two new naphthalenediimide (NDI) chromophores; (2Z,2'Z)-3,3'-(5,5'-(2,7-dioctyl-1,3,6,8-tetraoxo-1,2,3,6,7,8-hexahydrobenzo [lmn][3,8]phenanthroline-4,9-diyl)bis (thiophene-5,2-diyl))bis(2-(4-(trifluoromethyl)phenyl) acrylonitrile) (F1) and (2Z,2'Z)-3,3'-(5,5'-(2,7-dioctyl-1,3,6,8-tetraoxo-1,2,3,6,7,8-hexahydrobenzo [lmn] [3,8] phenanthroline-4,9-diyl)bis(thiophene-5,2-diyl))bis(2-(3,5-bis (trifluoroomethyl)phenyl) acrylonitrile) (F2). Both compounds are thermally stable as confirmed by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC), and are employed in perovskite solar cells (PSCs), making F1 and F2 promising candidates as electron transfer layers (ETL). Further, F1 and F2 were utilized as electron transport layers (ETLs) in inverted PSC assemblies. The overall power conversion efficiency (PCE) of inverted PSC devices constructed using F1 layer was 10.2 %, with circuit current density (J(sc)) of 24.17 mAcm(-2) and open circuit voltage (V-oc) of 0.81 V, and fill factor (FF) of 52 %, while PSCs constructed using F2 had 9.1 % PCE, J(sc) of 24.35 mAcm(-2), V-oc of 0.83 V, and FF of 45.4 %. The performance of PSCs are mainly attributed to the presence of -CF3 functional groups in F1 and F2.