Electrical properties of TiOx bilayer prepared by atomic layer deposition at different temperatures
Takeya Mochizuki, Kazuhiro Gotoh, Yasuyoshi Kurokawa, Noritaka Usami
Nagoya University, Nagoya, Japan

The conversion efficiency of crystalline silicon heterojunction solar cells is increased by carrier selective contacts (CSCs) thanks to the combination of conductive and passivating layers. Titanium oxide (TiOx) has been intensely investigated since it could act as an electron-selective contact and passivating layer on crystalline silicon (c-Si). However, the conversion efficiency of the solar cells employing a thin TiOx layer prepared by atomic layer deposition (ALD) is limited due to its relatively high contact resistivity even for » 3 nm-thick TiOx.
In this work, we propose the titanium oxide (TiOx) bilayer consisting of the TiOx layers prepared at deposition temperature of 100 and 150 °C by atomic layer deposition (ALD) based on the concept of the combination of conductive and passivating layers. It is revealed that the TiOx single layer prepared at 100 °C contain more oxygen vacancies than those prepared at 150 °C, leading to poor passivation performance and lower contact resistivity. On the other hand, the TiOx single layer with few oxygen vacancies was formed at 150 °C, resulting in high passivation performance and higher contact resistivity.
The TiOx bilayer shows higher electrical properties as CSCs in comparison with a TiOx single layer prepared at both 100 and 150 °C. The enhanced electrical properties are originated from higher passivation performance and lower contact resistivity of TiOx layers prepared at 150 and 100 °C, respectively. These results suggest that modulation of the deposition temperature during ALD process can improve the functionality of ALD-materials.