Broadband‐Solubility Diketopyrrolopyrrole Derivative with Both Polar Cyano and Nonpolar Alkyl Groups for Stable Organic Photosensors and Diffusion‐Processed Organic Solar Cells

A small‐molecular diketopyrrolopyrrole (DPP) derivative with cyano groups, (2E,2′E)‐diethyl‐3,3′‐((5,5′‐(2,5‐bis(2‐ethylhexyl)‐3,6‐dioxo‐2,3,5,6‐tetrahydropyrrolo[3,4‐c]pyrrole‐1,4‐diyl) bis(thiophene‐5,2‐diyl))bis(4,1‐phenylene)) bis (2‐cyanoacrylate) (EHTPPD‐ECPA), was synthesized via Suzuki‐coupling reaction. The synthesized EHTPPD‐ECPA exhibited a broadband solubility in both polar and nonpolar solvents due to the presence of both polar (cyano) and nonpolar (alkyl) groups. A bright pink photoluminescence (PL) was measured from EHTPPD‐ECPA solutions, whereas almost no PL was observed from the EHTPPD‐ECPA films because of high intermolecular stacking (band gap=1.7 eV). EHTPPD‐ECPA was found to act as an electron‐donating component in all‐small‐molecular bulk heterojunction layers for organic photosensors (photodetectors), while it played a critical role in improving the efficiency of diffusion‐processed polymer/fullerene solar cells with the mixed electron‐donating layers.