NOVELTY - An isothermal thermovoltaic device (ITD) includes an active layer (M-A) for intrinsically transducing thermal energy into electrical energy; two electrical contacts (C1, C2) each having a respective work function; a first electron diffusion barrier (B) positioned between and in electric communication with the active layer and the first electrical contact; a second electron diffusion barrier positioned between and in electric communication with the active layer and the second electrical contact.    USE - Isothermal thermovoltaic device (ITD) for simultaneously generating electrical power and cooling.    ADVANTAGE - The ITD device can achieve high efficiency operation in isothermal environments.    DETAILED DESCRIPTION - An ITD comprises an active layer (M-A) for intrinsically transducing thermal energy into electrical energy; two electrical contacts (C1, C2) each having a respective work function; a first electron diffusion barrier (B) positioned between and in electric communication with the active layer and the first electrical contact; and a second electron diffusion barrier positioned between and in electric communication with the active layer and the second electrical contact. The two work functions are nonidentical. The transduction of thermal energy into electrical energy yields thermally generated electrical carriers of both positive and negative charge. Thermally generated electrical carriers are separated according to charge to the first or second electric contact, thus lowering the average thermal energy of the active layer. INDEPENDENT CLAIMS are included for:    (1) a fluid treatment system for removing a first fluid from a second fluid comprising an ITD device, a fluid conduit, and a collector for collecting condensate;    (2) a system for increasing the efficiency of a vehicle engine by cooling the engine to generate electrical power, comprising an ITD device, a vehicle engine in thermal contact with the ITD device, and a vehicle engine in electrical contact with the ITD device; and    (3) a system for energy storage and recovery, comprising a heat sink, an electric resistor circuit, and an ITD device.    DESCRIPTION OF DRAWING(S) - The drawing shows a side view of an ITD device.    Electron diffusion barrier (B)    Electrical contacts (C1, C2)    Active layer (M-A)    Silicon substrate base (S-B)