Electrovoltaic (EV) effect provides a way of generating voltage across an unbiased junction under dark. Electrovoltaic (EV) cell in its simplest form is a device based on n(+)-p-n(+) (or p(+)-n-p(+)) like structure in which if one p-n junction is subjected to an external forward bias, then, a voltage is developed across the other p-n junction such that the n-side gets a negative polarity with respect to the p-side. Connecting to a load across one of the n(+)-p junctions a bipolar transistor can be operated as a three-terminal EV cell. A new device henceforth known as electrophotovoltaic (EPV) cell wherein EV and PV effects could be expected to work cooperatively was also realized. It is based on a structure which is a combination of n(+)-p-n(+) EV and n(+)-p-p(+) photovoltaic (PV) cell structures having a common n(+)-p junction and is able to operate in EV, PV and EPV modes. We have developed one-dimensional physical models of EV and EPV cells and have applied them to explain the observed I-V characteristics of an n-p-n silicon bipolar transistor 2N3055 in EV mode and the EPV cell in EV, PV and EPV modes. While the photovoltaic efficiency eta(PV) decreases slowly with d/L, where d is the thickness and L is the diffusion length of minority carriers in the base region, the electrovoltaic efficiency eta(EV) has a strong dependence on d/L and decreases sharply with increase in d/L. Transistor 2N3055 with d/L = 0.7 demonstrated eta(EV) > 60%, whereas, our EPV cell with d/L > 2.7 had eta(EV) < 3%. However, in the EPV cell, the PV and the EV effects were indeed found to work cooperatively and the output power was enhanced in the EPV mode over the PV mode value although the efficiency eta(EPV) was less than 4.5%. To achieve substantially high values of efficiencies in EV and EPV modes the EPV cell should be designed to have d/L much less than 1.