Macroporous Silicon as a Model for Silicon Wire Array Solar Cells

Abstract

Macroporous silicon samples have been investigated in photoelectrochemical cells, and their behavior has been compared to that of conventional, planar, Si/liquid junctions. The liquid electrolyte junction provided a conformal contact to the macroporous Si and allowed assessment of the trade-offs between increased surface area and decreased carrier collection distances in such systems relative to the behavior of planar semiconductor/liquid photoelectrochemical junctions. The electrolyte contained the dimethylferrocene/dimethylferrocenium redox system in methanol because this system has been shown previously to produce bulk recombination-diffusion-limited contacts at planar Si(100) electrodes under 100 mW cm^(-2) of simulated air mass 1.5 illumination. Introduction of a network of ∼2−3 μm diameter, ∼80 μm long pores into the Si was found to slightly reduce the short-circuit photocurrent density and the open-circuit voltage of the system, but energy-conversion efficiencies in excess of 10% were nevertheless obtained from such samples. This system therefore validates the concept of using interpenetrating networks to produce efficient solar energy conversion devices in systems that do not have long carrier collection distances.