Recently, indoor energy harvesting technology has received considerable attention as a remote power source for Internet of Things (IoT) devices [1-2]. In IoT applications, wired power connections to many individual IoT devices is not practical. As with solar cells, if the remote energy harvester operates independently and does not have a large battery, but can supply enough power for operation, then permanent operation of an IoT device is possible and no physical power line is required. Amorphous silicon (a-Si:H) solar cells have optical bandgaps of approximately 1.7 eV, and absorb visible light (350–800 nm) well, making a-Si:H solar cells suitable for generating electricity from indoor light sources such as light-emitting diodes (LED) and fluorescent lamps . Therefore, a-Si:H cells can be used as power sources for IoT devices by harvesting indoor light energy. Among many IoT devices, transparent IoT devices incorporating transparent electronic devices, such as transparent touch screens and displays, are being developed. In addition, it is required to apply a transparent solar cells for aesthetic effect, and our research group has studied transparent solar cells for application to building windows [4-5]. However, for indoor photovoltaics, there have been little studies on the optimized structures for transparent solar cells.