Incompatible Length Scales in Nanostructured Cu₂O Solar Cells

Abstract

Electrodeposited Cu 2 O-ZnO heterojunctions are promising low-cost solar cells. While nanostructured architectures improve charge collection in these devices, low open-circuit voltages result. Bilayer and nanowire Cu 2 O-ZnO heterojunction architectures are systematically studied as a function of the Cu 2 O layer thickness, ZnO nanowire length, and nanowire seed layer. It is shown that a thick depletion layer exists in the Cu 2 O layer of bilayer devices, owing to the low carrier density of electrodeposited Cu 2 O, such that the predominant charge transport mechanisms in the Cu 2 O and ZnO are drift and diffusion, respectively. This suggests that the low open-circuit voltage of the nanowire cells is due to an incompatibility between the nanostructure spacing required for good charge collection ( < 1 μ m) and the heterojunction thickness necessary to form the full built-in potential that inhibits recombination ( > 2 μ m). The work shows the way to improve low-cost Cu 2 O cells: increasing the carrier concentration or mobility in Cu 2 O synthesized at low temperatures.

A Review on Cu<SUB>2</SUB>O and Cu<SUP>I</SUP>-Based <I>p</I>-Type Semiconducting Transparent Oxide Materials: Promising Candidates for New Generation Oxide Based Electronics

“…Very recently a work has been published on nanostructured Cu 2 O based solar cells by the group of MacManus-Driscoll. 137 This group has done a systematical study on bilayer and nanowire Cu 2 O/ZnO heterojunction solar cells as a function of the Cu 2 O layer thickness, ZnO nanowire length and nanowire seed layer. understanding on nanostructured device physics.…”

Growth of ∼5 cm2V−1s−1 mobility, p-type Copper(I) oxide (Cu2O) films by fast atmospheric atomic layer deposition (AALD) at 225°C and below

“…For Cu 2 O in inorganic solar cells, high carrier concentrations of at least 10 16 cm −3 are necessary to achieve the full depletion layer width, thus allowing high open circuit voltage and near theoretical J sc values to be obtained. 13 Cu 2 O thin films can be deposited by several methods including pulsed laser deposition (PLD), 8 sputtering, 14 thermal oxidation, 15 spray pyrolysis 16 and electrochemical deposition. 17 Sputtering appears to be the most successful vacuum method for achieving high mobilities at low temperatures.…”

Effect of seed layer on optical properties and visible photoresponse of ZnO/Cu2O composite thin films

“…It is a promising metal oxide for applications in solar cells [1,2], photocatalysts [3,4], and photosensors [5,6], as it has high visible light absorption, is nontoxic, and made from abundant raw materials at low cost. Zinc oxide (ZnO) is a direct band gap n-type semiconductor with an energy gap of $ 3.37 eV and a relatively large exciton binding energy of 60 meV at room temperature.…”