Investigation of properties of InGaN-based vertical-type solar cells with emission wavelengths in ultraviolet-blue-green regions

Seung Hwan Kim,Jae Phil Shim,Hyung Jo Park,Seong Ran Jeon,Hyun Ho Park,Young Ho Song,Dong Sun Lee,Gye Mo Yang,Seung Hyeon Yang

doi:10.1117/1.jpe.4.043096

Abstract

We investigate the properties of InGaN-based vertical-type solar cells having wavelengths ranging from the ultraviolet to green regions. It is well known that InGaN-based solar cells require a high indium composition to obtain high conversion efficiency. However, although InGaN-based solar cells with a high indium composition have been fabricated, their conversion efficiency has not sufficiently increased. Therefore, to further understand carrier transport, we measured the bias-dependent external quantum efficiency. For vertical-type green solar cells with a high indium composition, we confirmed that they have a higher short circuit current than other samples tested due to their broader overlapping region with the solar spectrum, though their fill factor remained low due to their high barrier height and strong piezoelectric field, which caused a reduction in the carrier tunneling rate.

Highlights

To obtain a high conversion efficiency, most InGaN solar cells studies have been confined to the green region, requiring an indium content of about 15% to 30%
We investigate the properties of vertical-type solar cells (VSCs) having InGaN/ (Al)GaN multiple quantum well (MQW) in terms of carrier transport, based on bias-dependent external quantum efficiency (EQE) measurements
The conversion efficiency of these VSCs is subsequently found to be higher than for lateral-type solar cells due to a larger amount of light absorbed by the bottom reflector;[25,26] the textured n-GaN top surface is seen to absorb most of the light

Summary

Introduction

III-V nitride material systems, which include AlN, GaN, InN, and their alloys, have been widely investigated due to their tunable energy bandgaps and application in light-emitting diodes (LEDs), laser diodes, and solar cells.[1,2] The bandgap of InGaN material systems covers emission wavelengths from the near-ultraviolet (UV) to green regions, which essentially includes the entire functional range of the solar spectrum.[3,4,5] To obtain a high conversion efficiency, most InGaN solar cells studies have been confined to the green region, requiring an indium content of about 15% to 30%.6–9 The efficiency of InGaN solar cells having an emission wavelength in the green region is high due to the high In composition, compared with those under a green wavelength, though their fill factor (FF) remains low due to their perceived poor crystal quality. We investigate the properties of vertical-type solar cells (VSCs) having InGaN/ (Al)GaN MQWs in terms of carrier transport, based on bias-dependent external quantum efficiency (EQE) measurements. The conversion efficiency of these VSCs is subsequently found to be higher than for lateral-type solar cells due to a larger amount of light absorbed by the bottom reflector;[25,26] the textured n-GaN top surface is seen to absorb most of the light. These solar cell structures were grown using metal organic chemical vapor deposition (MOCVD), and all devices were fabricated using a conventional vertical LED process

Experiments

Results and Discussion

Conclusion