The high efficiency and long-term stability of crystalline silicon (Si) makes this the preferred material for solar cells. The capacity to impart transparency to the material would broaden crystalline Si solar cell applications in An opaque solar cell (left) compared to a transparent solar cell with microholes (right). Source: Ulsan National Institute of Science and Technology building-integrated photovoltaics, vehicles and personal electronics. Researchers in South Korea have found an opening to the realization of this property: punch microholes in crystalline Si wafers.

Sizing and grid spacing of the holes were guided by numerical simulations of incident radiation and its reflection, transmission and diffraction through openings of varying widths. Holes of 90 to 100 μm diameter were placed in 200 μm thick wafers by a deep reactive ion etching process. The spacing of holes was much smaller than 1.75 mm so that the pattern will be invisible even at a distance of 30 cm (12 in), considered the appropriate distance for using smartphones and other mobile devices.

The punctured wafer was then incorporated into a photovoltaic cell along with a doped-Si backplane and a grid-type upper metal electrode. A maximum power conversion efficiency of 12.2% was measured, indicating potential for using the glass-like Si in transparent power-generating window and other applications.

The research conducted at Ulsan National Institute of Science and Technology and Korea University is published in Joule.