Three hundred-nanometre thick films of n-InSe have been vacuum-deposited by flash evaporation on conducting indium oxide film coated clean glass substrates held at 373 K at 6.6 × 10-3 Pa pressure. These InSe films have been used as photoelectrodes in a photoelectrochemical (PEC) cell with graphite as the counter electrode, the saturated calomel electrode as the reference electrode and aqueous polyiodide electrolyte (with different pHs) as the redox electrolyte. PEC cells have been characterised by making I-V and C-V measurements under different experimental conditions, i.e., using the as-grown InSe films as photoelectrodes before and after surface treatment and after annealing and/or etching and for different pHs of the electrolyte. The optimum pH has been found to be about 6.2. It is also found that surface treatment and annealing leads to increase in the efficiency of the PEC solar cell. The open circuit voltage and photo current density are found to be of the order of 580 mV and 3000 μA/cm2, respectively under AM1 condition. © 1997 Elsevier Science S.A.