We present the results of a new self-consistent analytical model for the calculation of the dark current and the electric-field and space-charge distributions in quantum well infrared photodetectors (QWIPs). This model takes into account thermionic emission from the QWs, tunneling injection of electrons from the emitter contact, transport of the excited and injected electrons across an active region of a QWIP and their capture into the QWs. It is shown that the electric-field and space-charge distributions in the QW structure are nonuniform in general. The character of their nonuniformity is determined by the relationships between the structural parameters, parameters of elementary processes, and bias voltage.