Fig. 3

Mechanism. a Asymmetric diffusion and electromigration of electrons and holes result in the redistribution of electric potential along the GO strip and local low electric potential in the illuminated area. When illumination was on an off-center position (left and right), an electric potential difference (∆V) can be found. b MD simulations confirm the generation of horizontal cationic transport, depending on the illumination position. c, d The polarity and magnitude of ∆V and photocurrent depend on illumination position and light intensity. e Under 10-fold concentration gradient, photo-induced ion transport counterbalances diffusion current (I_diff). Over a threshold light intensity, ionic current reverses to anti-gradient direction. f Similar trends were found under 5- to 15-fold concentration gradients. The threshold light intensity increases with the concentration gradient. The dashed line in (f) indicates I_diff