A photovoltaic cell comprises an electrode layer, a photovoltaic layer, a hole transport layer, a conductive layer and a counter electrode layer stacked in this order. Random pulses are generated by comparing a voltage level obtained by amplifying a voltage level of a thermal noise produced by a thermal noise generating device with a reference voltage level. De-identification includes field-level one-way encryption. The sensor may be used to sense the state of the folding screen such that the folding screen, when it is unfolded, displays together with the main display screen, and such that the main display screen displays by itself when the folding screen is folded.