A 53 high efficiency GaAs vertically integrated multi-junction laser power converter

摘要

Power-by-light schemes to provide electrical power to remote opto-electronic modules typically involve the use of multi-segmented photovoltaic (PV) cells or commonly known as laser power converters (LPC) illuminated by an optical fiber to produce output voltages between 2 and 12 volts, with up to several hundred milliwatts of electrical power. Typically these photovoltaic devices are based on a GaAs single junction cell grown on semi-insulating GaAs substrates and they are further segmented and connected in series depending on the output voltage required. Theoretically, these cells should have efficiencies near 60% but currently these cells have efficiencies only in the range of 40 to 45%. Optical losses due to high grid metal coverage and cell isolation trench can reduce efficiency by nearly 10%. In order to eliminate the losses in the multi-segmented cells and to improve the efficiencies further we have designed a vertical multi junction device. The vertical multi-junction approach has several advantages over the multi-segmented approach. The advantages are; a) reduction in optical losses due to trench formation, b) lower metal obscuration losses, due to lower current density in the device, c) reduction of sheet conduction losses, and d) simple process to fabricate the devices. We have successfully designed and fabricated a new vertical multi-junction 2V laser power converter with an efficiency of over 53%, a considerably higher efficiency than the regular multi-segmented 2V GaAs laser power converter and this is the highest efficiency reported so far for a photovoltaic device.