3-D Solar Cells Based on Radial Silicon Heterojunctions Exploiting Microhole Lattices

In this letter, 3-D solar cells based on radial amorphous/crystalline silicon heterojunctions (SHJs), which are formed on 2-D lattices of vertical high aspect-ratio microholes (MHs) etched in crystalline silicon (c-Si) substrates, are realized with conversion efficiency of ~ 3%. Silicon high aspect-ratio MH lattices, with hole diameter of a few micrometers and hole depth of tens micrometers, are produced on n-type c-Si substrates by electrochemical micromachining (ECM) technology with low reflectance ( depending on diameter and depth) in the wavelength range between 400 and 900 nm, which is commonly exploited for solar cell application. The radial SHJ solar cells are obtained by successive quasi-conformal deposition of hydrogenated amorphous silicon (a-Si:H) i-layer and p-layer, respectively, via plasma-enhanced chemical vapor deposition at 200°C, within the MH lattices, and subsequent indium tin oxide and Ag deposition for the formation of electrical front and back contacts, respectively. Experimental conversion efficiencies up to 2.72% are obtained under standard AM1.5 illumination with intensity of 100 mW/cm², thus envisaging that ECM technology can be successfully adopted to realize efficient 3-D solar cells based on radial p-n junctions exploiting high aspect-ratio MH lattices, in particular, or other microstructures, in general.