Plasma-Enhanced Atomic Layer Deposition of TiN Thin Films as an Effective Se Diffusion Barrier for CIGS Solar Cells.

Seung Il Jang,Woo-Jae Lee,Hyoungseok Moon,Shinho Kim,Hyun-Jae Woo,Eun-Kyong Koh,Se-Hun Kwon

doi:10.3390/nano11020370

Abstract

Plasma-enhanced atomic layer deposition (PEALD) of TiN thin films were investigated as an effective Se diffusion barrier layer for Cu (In, Ga) Se2 (CIGS) solar cells. Before the deposition of TiN thin film on CIGS solar cells, a saturated growth rate of 0.67 Å/cycle was confirmed using tetrakis(dimethylamido)titanium (TDMAT) and N2 plasma at 200 °C. Then, a Mo (≈30 nm)/PEALD-TiN (≈5 nm)/Mo (≈600 nm) back contact stack was fabricated to investigate the effects of PEALD-TiN thin films on the Se diffusion. After the selenization process, it was revealed that ≈5 nm-thick TiN thin films can effectively block Se diffusion and that only the top Mo layer prepared on the TiN thin films reacted with Se to form a MoSe2 layer. Without the TiN diffusion barrier layer, however, Se continuously diffused along the grain boundaries of the entire Mo back contact electrode. Finally, the adoption of a TiN diffusion barrier layer improved the photovoltaic efficiency of the CIGS solar cell by approximately 10%.

Highlights

As the demand for electricity increases, the environmental concerns increase mainly owing to greenhouse gas emissions
A TiN layer was introduced on the inside of the Mo layer to control the appropriate thickness of the MoSe2 layer, preventing Se from randomly diffusing into the Mo layer
TiN diffusion layer was successfully prepared by the Plasma-enhanced atomic layer deposition (PEALD) process using a TDMAT precursor and N2 plasma

Summary

Introduction

As the demand for electricity increases, the environmental concerns increase mainly owing to greenhouse gas emissions. With the development of a variety of renewable energy sources, photovoltaic technologies that produce electricity have attracted the most attention owing to their reliable, potentially infinite, and clean sunlight source. A CIGS thin film is typically prepared by a three-stage co-evaporation or two-step process. The two-step process involves precursor deposition and selenization. Selenization is carried out using H2 Se or Se vapor gas [5]. This two-step process has been recently preferred because of its low costs and large-area approach that can be realized with a non-vacuum atmospheric process, resulting in a relatively uniform composition of the CIGS layer

Methods

Results

Conclusion