Evaluation method of the light-trapping structure for a transparent thin-film silicon solar cell with low-illuminance condition

•Transparent solar cells were made for building-integrated photovoltaics (BIPV).•Front electrode was etched with time to enhance light-trapping in absorption layer.•High current was obtained in low light-trapping structure under low light intensity.•Textured structure was considered to make entangled performance with light intensity.•The rate equation clarified optical gain and electrical loss with light intensity.