Tailoring Optoelectronic Properties of Optical Hybrid Materials via Print-Enabled Doping

While the optoelectronic properties of polymers can be tuned through doping and nanomaterials incorporation, conventional sample-by-sample synthesis is often time-consuming and limits efficient exploration of fundamental structure–property relations due to the vast material space. Here, we show the feasibility of using a direct-ink-writing-based combinatorial printing approach as a printing-enabled doping tool for fabricating PANI films with continuously varying doping states and nanofillers. A continuous protonation-state gradient was first printed through pH-mediated deprotonation of polyaniline emeraldine salt (PANI-ES). The printed film exhibited a gradual color transition from deep green to dark navy, while spatially resolved spectroscopic analysis verified the corresponding variation in the protonation state across the film. This deprotonation was further correlated with an increase in the estimated direct optical band gap from 2.14 to 2.41 eV, as determined from separately prepared PANI samples at different pH values. In addition, an organic/inorganic compositional gradient was printed by varying the selenium nanowire (Se NW) content, producing a dark-green-to-reddish color transition, and elemental analysis verified the increase in Se percentage across the film. As a proof of concept, we fabricated in-plane photodetectors from individually prepared pristine PANI and PANI/Se NW hybrid films that each had a uniform composition but contained different Se NW loadings. Their optoelectronic response varied nonmonotonically with Se NW content, reaching a maximum at 20 wt % Se NW. Compared with pristine PANI, the 20 wt % Se NW devices achieved an approximately two-fold higher normalized photoresponse, along with increases in responsivity and specific detectivity of approximately 84% and 95%, respectively. This work indicates the potential of printing-enabled doping for efficient structure–property studies and optoelectronic materials design.