To investigate semi-transparent solar cells, a-Si:H and a-SiGe:H thin film cells have been prepared. In a fabrication of a-Si:H solar cell, top transparent conductive oxide (TCO) thicknesses were varied and the cell with TCO thickness of 300 nm or more exhibited cell efficiency around 5.5%. In particular, a-Si:H cell with 300 nm thick TCO shows average transmittance of visible light around 21.7%, which also shows high efficiency as well. In this experiment, the efficiency and the transmittance did not show a trade-off as is usually observed with conventional semi-transparent solar cells, which is meaningful to control them independently. The a-SiGe:H solar cell with 500 nm thick TCO showed an efficiency of 5.93% and an average transmittance of 17.9%. In spite of its lower transmittance compared to the a-Si:H cell, it can be favorably applied to semi-transparent solar cells. (C) 2013 Elsevier B. V. All rights reserved.