This study aims to develop bio-based interfacial materials for organic photovoltaic applications by engineering carotenoid-derived molecular frameworks with favorable energy level alignment and enhanced light-harvesting capability.
Three diphenylamine (DPA)-functionalized diquinoxalinocarotene end-group isomers (DQC-DPA1, DQC-DPA2 and DQC-DPA3) were synthesized via Pd-catalyzed Buchwald–Hartwig coupling of a dibrominated carotenoid precursor (2BrDQC) with bis(4-methoxyphenyl)amine and isolated by silica gel column chromatography. Structures were confirmed by 1H/13C nuclear magnetic resonance spectroscopy and high-resolution matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. Optical and electrochemical properties were characterized by UV–vis spectroscopy and cyclic voltammetry. Photovoltaic performance was assessed in inverted organic solar cell (OSC) (ITO/ZnO/D18:L8-BO/anode interfacial layer [AIL]/Ag) and perovskite solar cell (PSC) (glass/ITO/hole-transport layer [HTL]/FA0.8Cs0.2PbI1.6Br1.4/C60/bathocuproine/Ag) device architectures. Thin-film morphology and surface properties were characterized by atomic force microscopy, X-ray diffraction and water contact angle measurements. Photochemical stability was assessed through degradation studies.
All three isomers exhibited broad visible-light absorption (300–700 nm) with molar extinction coefficients several-fold higher than the parent diquinoxalino[1,2-c:1′,2′-c′]-β-carotene (DQC) and significantly elevated highest occupied molecular orbital levels (−4.72 eV) because of donor–acceptor interactions. Terminal-group isomerism primarily regulated solid-state packing and optical absorption rather than frontier orbital energies. In OSC devices, the asymmetric isomer DQC-DPA2 delivered superior performance (power conversion efficiency [PCE] = 2.94%) compared with the symmetric isomers DQC-DPA1 (0.66%) and DQC-DPA3 (0.35%), suggesting that molecular symmetry plays an important role in governing interfacial charge-extraction behavior. DQC-DPA1 as an HTL in PSCs underperformed relative to the 4-(diphenylamino)cyclohexylbenzoic acid reference (PCE 8.74% vs 18.42%), indicating the need for further optimization in perovskite architectures.
To the best of the authors’ knowledge, this study represents the first demonstration of a bio-derived carotenoid-based material as an AIL in OSCs and the first systematic investigation of end-group isomerism effects in natural pigment-derived interfacial materials for photovoltaic applications.
