Titanium dioxide hole-blocking layer in ultra-thin-film crystalline silicon solar cells

TL;DR

This paper introduces a novel TiO2-based hole-blocking layer for ultra-thin crystalline silicon solar cells, significantly reducing recombination losses and improving efficiency to approach that of thicker cells.

Contribution

The study presents a new TiO2 MIS contact design that enhances open circuit voltage and reduces recombination in ultra-thin c-Si solar cells, enabling high efficiency at lower costs.

Findings

Achieved 645 mV Voc with TiO2 MIS contact

Reduced hole recombination at the contact interface

Enabled high-efficiency ultra-thin silicon solar cells

Abstract

One of the remaining obstacles to approaching the theoretical efficiency limit of crystalline silicon (c-Si) solar cells is the exceedingly high interface recombination loss for minority carriers at the Ohmic contacts. In ultra-thin-film c-Si solar cells, this contact recombination loss is far more severe than for traditional thick cells due to the smaller volume and higher minority carrier concentration of the former. This paper presents a novel design of an electron passing (Ohmic) contact to n-type Si that is hole-blocking with significantly reduced hole recombination. This contact is formed by depositing a thin titanium dioxide (TiO2) layer to form a silicon metal-insulator-semiconductor (MIS) contact. A 2 {\mu}m thick Si cell with this TiO2 MIS contact achieved an open circuit voltage (Voc) of 645 mV, which is 10 mV higher than that of an ultra-thin cell with a metal contact. This MIS contact demonstrates a new path for ultra-thin-film c-Si solar cells to achieve high efficiencies as high as traditional thick cells, and enables the fabrication of high-efficiency c-Si solar cells at a lower cost.