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Increased Light Emitting Diode Efficiency

IP.com Disclosure Number: IPCOM000078870D
Original Publication Date: 1973-Mar-01
Included in the Prior Art Database: 2005-Feb-26
Document File: 2 page(s) / 39K

Publishing Venue

IBM

Related People

Potemski, RM: AUTHOR [+2]

Abstract

The external efficiency of light-emitting diodes (LED's) is reduced due to self-absorption of the light produced by the diode. Methods used to circumvent this shortcoming have been shaping of the diodes to increase the escape angle, transparent substrates, etc. All of these methods have been attempts to limit self-absorption. The device of Fig. 1 shows an arrangement for increasing external efficiency by converting normally wasted, self-absorbed light back to useful power.

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Increased Light Emitting Diode Efficiency

The external efficiency of light-emitting diodes (LED's) is reduced due to self-absorption of the light produced by the diode.

Methods used to circumvent this shortcoming have been shaping of the diodes to increase the escape angle, transparent substrates, etc.

All of these methods have been attempts to limit self-absorption.

The device of Fig. 1 shows an arrangement for increasing external efficiency by converting normally wasted, self-absorbed light back to useful power.

The semiconductor device of Fig. 1 consists of several PN junctions, one or more of which emit light, such as a light-emitting diode 1 (LED) and one or more photovoltaic devices (PVD) 2 sensitive to the emitted light. They are constructed so that the light that does not leave the viewing surface of diode 1 is absorbed by the PVD 2 part of the structure. The power thus developed may be added to the input of LED device 1 or used to power a secondary LED device 3.

The device can be envisioned by considering an LED 1 and PVD 2 as separate units and then stacking them to form a single unit.

One constraint in such a structure is that the voltage developed by the PVD must be at least the same as the voltage applied to the LED. This cannot occur. Therefore, a small voltage represented by battery 4 in Fig. 2 must be added in series with PVD 1, in order to achieve the necessary bias for LED 3. Alternately, this bias could be developed by segmenting PVD 2 into por...