Promoting the nonlinear optical absorption of conjugated polymers by in-gap states modulation via chemical dedoping

With the development of laser technology, nonlinear optical (NLO) materials are attracting more and more attention because of their significant application potential in optical limiting, optical switching, photonic diode, sub-bandgap photoelectric detection, Q-switched/mode-locked pulse laser generation, and so on. In this paper, a convenient dedoping strategy is developed to promote the NLO response of conjugated polymer based on in-gap states modulation. The poly(3,4-ethylene dioxythiophene):poly(styrene sulfonate), PEDOT:PSS, exhibits remarkably enhanced nonlinear absorption at different dedoping levels in comparison with the pristine one. The nonlinear absorption coefficient can reach -1578 ± 49 (lightly dedoped sample) and 612 ± 43 cm GW⁻¹ (highly dedoped sample) under 800 nm laser excitation. The performance is 6 and 2 times that of the pristine PEDOT:PSS, respectively. The optical nonlinearity of dedoped films is also superior to many excellent NLO materials. The modulation of in-gap states alters the excitation process during the NLO response and accordingly the corresponding performance. In-gap states modulation can be applied to promote the NLO performance of other conjugated polymers, e.g. poly(3-hexylthiophene).