Polymer Embedded Silicon Microwires for Colorless, Transparent, Flexible Solar Cells

Abstract

Transparent solar cells have potential applications such as building integrated photovoltaics (BIPV) and photovoltaic chargers for portable electronics. Several groups reported transparent solar cells technologies based on perovskite, organic, or dye-sensitized solar cells, taking advantage of relatively their high energy bandgaps. Unfortunately, those cells suffer from low efficiencies (h < ~ 5%), and long-term stability issues. More importantly, they have colors typically orange or red because those cells are transparent only to the limited solar spectrum from orange/red to infrared. In this work, we demonstrated a colorless transparent solar cell, which was fabricated using a Si microwires (SiMWs) array embedded in a transparent flexible polymer matrix such as PDMS or BCB. For the fabrication of SiMWs of 1 ~ 2 mm diameter and ~ 30 mm length, a p-type Si wafer was photo-lithographically patterned in a hexagonal array and etched using a deep Si etcher. Subsequently, n-type emitter layer was formed by a POCl3 diffusion process, making a core-shell type of n/p junction. Finally, the MWs array was embedded with BCB microwires are lifted off from the silicon substrate, followed by top and bottom ohmic metallization using transparent conducting oxides and silver nanowires. The SiMWs-polymer composite solar cell has an efficiency of ~ 5% and transparency of ~ 10% with color rendering index close to 100. In this presentation, optical simulation as a function of the diameter and pitch between microwires by COMSOL wave optics module and the trade-off relationship of transmittance and efficiency will be also included.