Enhanced generation of carriers when a thermophotovoltaic cell is placed in submicron proximity to a heated surface is demonstrated using custom-designed InAs photodiodes and special silicon-based heater chips produced using microelectromechanical system techniques. The short-circuit current of the photocells is shown to increase sharply (up to fivefold) when the spacing between the heater and photodiode surfaces is reduced, while at the same time, the heater temperature decreases, consistent with increased radiative transfer between the two surfaces. By varying the spacing sinusoidally (at up to 1 kHz), it is demonstrated that the increase in the short-circuit current occurs in phase with the decrease in separation, thereby ruling out thermal effects. It is argued that the increase in short-circuit current is due to increased evanescent coupling of blackbody radiation from the hot surface to the cold photocell, consistent with recent theoretical predictions. The demonstration of this effect is the initial step in the development of a class of energy conversion devices.

Abstract. This paper discusses advances made in the field of Micron-gap ThermoPhotoVoltaics (MTPV).Initial modeling has shown that MTPV may enable significant performance improvements relative to conventional far field TPV. These performance improvements include up to a lOx increase in power density, 30% to 35% fractional increase in conversion efficiency, or alternatively, reduced radiator temperature requirements to as low as 550°C. Recent experimental efforts aimed at supporting these predictions have successfully demonstrated that early current and voltage enhancements could be done repeatedly and at higher temperatures. More importantly, these efforts indicated that no unknown energy transfer process occurs reducing the potential utility of MTPV. Progress has been made by running tests with at least one of the following characteristics relative to the MTPV results reported in 2001: .Tests at over twice the temperature (900°C). .Tests at 50% smaller gaps (0.12 J.lm) .Tests with emitter areas from 4 to 100 times larger (16 nun2 to 4 cm2). .Tests with over 20x reduction in parasitic spacer heat flow.Remaining fundamental challenges to realizing these improvements relative to the recent breakthroughs in conventional far field TPV include reengineering the photovoltaic (PV) diode, filter, and emitter system for MTPV and engineering devices and systems that can achieve submicron vacuum gaps between surfaces with large temperature differences.

Abstract. This paper discusses advances made in the field of Micron-gap ThermoPhotoVoltaics (MTPV).Initial modeling has shown that MTPV may enable significant performance improvements relative to conventional far field TPV. These performance improvements include up to a lOx increase in power density, 30% to 35% fractional increase in conversion efficiency, or alternatively, reduced radiator temperature requirements to as low as 550°C. Recent experimental efforts aimed at supporting these predictions have successfully demonstrated that early current and voltage enhancements could be done repeatedly and at higher temperatures. More importantly, these efforts indicated that no unknown energy transfer process occurs reducing the potential utility of MTPV. Progress has been made by running tests with at least one of the following characteristics relative to the MTPV results reported in 2001: .Tests at over twice the temperature (900°C). .Tests at 50% smaller gaps (0.12 J.lm) .Tests with emitter areas from 4 to 100 times larger (16 nun2 to 4 cm2). .Tests with over 20x reduction in parasitic spacer heat flow.Remaining fundamental challenges to realizing these improvements relative to the recent breakthroughs in conventional far field TPV include reengineering the photovoltaic (PV) diode, filter, and emitter system for MTPV and engineering devices and systems that can achieve submicron vacuum gaps between surfaces with large temperature differences.

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