n-InGaN/p-Cu2O core-shell nanowire (NW) p–n junctions enable efficient self-powered photoelectrochemical photodetectors (PEC PDs) in the visible. The photocurrent density under one-sun illumination is enhanced by 8 times compared to that of bare InGaN NW PEC PDs due to maximized photocarrier separation in the built-in electric field of the p–n junction. The responsivity reaches 173  μA/W under one-sun illumination. The response times of 30–40 ms are among the shortest achieved for PEC PDs. Together with the long-time stability and reusability, a robust, easy to fabricate, and easy to operate self-powered PEC PD is introduced.

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InN/InGaN quantum dots (QDs) are found to establish a nonlinear constant phase element (CPE) response over a wide frequency range, measured by electrochemical impedance spectroscopy. The intrinsic surface donors together with the near-surface electron accumulation layer form the fractional capacitor. The magnitude of the impedance and the phase angle depend on the QD structural parameters and contact area. Importantly, they consistently change with applied voltage, constituting the nonlinear CPE response. A noise-filtering DC voltmeter with the phase angle as readout is proposed.