High voltage bifacial amorphous Si quintuple-junction solar cells for IoT devices

Abstract

Abstarct A bifacial amorphous Si quintuple-junction solar cell was proposed as a power source for IoT devices. Conventionally, interconnection using laser processing has been widely adopted in consumer devices using solar cells as a power source in order to increase the operating voltage, but in this paper, we propose a method to make the output voltage 3 V or more by quintuple-junction. First, after describing the necessity of using the bifacial structure, a simple theoretical discussion on the layer thickness of each cell was made. In addition, a-SiOx:H/a-SiOx:H/a-Si:H/a-SiOx:H/a-SiOx:H quintuple-junction solar cells were fabricated by plasma CVD method. As a result, a very high open circuit voltage of 3.4 V was demonstrated under LED light illumination.

Bifacial amorphous Si quintuple‐junction solar cells for IoT devices with high open‐circuit voltage of 3.5V under low illuminance

“…Prior to fabricating the quintuple‐junction solar cells, a triple‐junction solar cell was fabricated with optical bandgaps and i‐layer thicknesses of E opt (1)=1.85 eV, 250nm, E opt (2)=1.75 eV, 430nm and E opt (3)=1.85 eV, 250nm, respectively. And at an irradiance of 10 and 1 mW/cm 2 , the open‐circuit voltages of 2.1 and 1.8V were obtained, respectively . In this way, by changing from triple‐junction to quintuple‐junction, we were able to improve the open‐circuit voltage of about 1.3V in the low illuminance region.…”

“…In the initial quintuple‐junction solar cells, the total film thickness was 2μm‐3μm, but the fill factor was very low of 0.3‐0.4 . By reducing the total thickness to 0.6‐0.8μm, we tried to improve the fill factor while maintaining a high open‐circuit voltage.…”

“…So far, interconnection has been required to obtain an operating voltage of several volts. In 2018, the author has experimentally shown that if a quintuple‐junction structure is fabricated with an amorphous Si solar cell, it generates a DC voltage of 3.5 V under low illuminance . The interconnection of thin film solar cells requires three scribing steps, but if high voltage can be generated with multiple junctions, it can be manufactured inexpensively without the need for a laser processing step.…”

Spectral response measurements of each subcell in monolithic triple-junction GaAs photovoltaic devices

“…GaAs, a-Si) have been proposed to obtain high output voltage in multijunction photovoltaic devices for laser power conversion and internet of things devices. [3][4][5] A high photovoltage can be applied to photoelectrochemical cells for solar water splitting, which provides direct conversion of solar energy into stored chemical energy. 6) To achieve such application of photovoltaic devices, high-efficiency photovoltaic devices using III-V semiconductors, such as GaAs, have been developed.…”

Flexible bifacial amorphous Si quintuple‐ and sextuple‐junction solar cells for Internet of Things devices

“…Energy conversion of single-junction solar cells under low illuminance is described in detail by Russo et al 3 We have already developed quintuple-junction amorphous Si solar cells as a solar cell that can generate a high voltage of 3 V or more without an interconnection. 4,5 Since wiring for integration is not required, it is possible to easily manufacture a cell having an extremely small area of mm size and further a cell having a large area of several tens of cm 2 depending on the output required. The feature of quintuple-junction amorphous Si solar cells is that it is composed of 5-junctions based on amorphous Si(O):H material in order to obtain an operating voltage of 3 V or more and has a bifacial device structure capable of receiving light on both sides so that the bottom cell can be designed to be thin.…”