10-20 nm thick ATM layers were prepared by spin coating (10-20 cycles) of a 10 mM solution of ATM, using dimethyl sulfoxide (DMSO) as solvent, onto the WSe 2 photocathodes. Because of the high boiling point of DMSO (189°C), the electrodes were dried in an evacuated desiccator at room temperature for 30 min. After drying, the electrodes were kept at 100 °C in an oven for 2 h. The ATM-coated WSe 2 films display a brownish color, see Supplementary Fig. . Characterization techniques. The structure, phase composition and rocking curves of the films were determined by X-ray diffraction (XRD) using a PANalytical XPert MPD diffractometer (CuKα=0.15408 nm). The morphology and the chemical element distribution of the films were studied by scanning electron microscopy (SEM) and energy dispersive X-ray fluorescence analysis (EDX) with a LEO GEMINI 1530 system.