Heterojunction Silicon Microwire Solar Cells

We report radial heterojunction solar cells of amorphous silicon on crystalline silicon microwires with high surface passivation. While the shortened collection path is exploited to increase the photocurrent, proper choice of the wire radius and the highly passivated surface prevent drastic decrease in the voltage due to high surface-to-volume ratio. The heterojunction is formed by depositing a similar to 12-16 nm of amorphous silicon on crystalline silicon wires of radius approximately equal to minority carrier diffusion length (similar to 10 mu m). In spite of very short carrier lifetime (<1 mu s), the microwire array devices generate photocurrent of similar to 30 mA/cm(2), and the same time, voltages close to 600 mV are achieved, leading to efficiency in excess of 12% in extremely short carrier lifetime silicon. We also find that formation of nanocrystallites of silicon in the deposited film results in loss of the expected passivation.