ALD of ZnO:Ti: Growth Mechanism and Application as an Efficient Transparent Conductive Oxide in Silicon Nanowire Solar Cells

Abstract

In the quest for replacement of indium-tin-oxide (ITO), Ti-doped zinc oxide (TZO) films have been synthesized by atomic layer deposition (ALD) and applied as n-type transparent conductive oxide (TCO). TZO thin films were obtained from titanium (IV) i-propoxide (TTIP), diethyl zinc and water, by introducing TiO2 growth cycle in a ZnO matrix. Process parameters such as the order of precursor introduction, the cycle ratio and the film thickness were optimized. The as-deposited films were analyzed for their surface morphology, elemental stoichiometry, optoelectronic properties and crystallinity, using a variety of characterization techniques. The growth mechanism was investigated for the first time by in situ quartz-crystal microbalance measurements. It evidenced different insertion modes of titanium depending on the precursor introduction, as well as the etching of Zn-Et surface groups by TTIP. Resistivity as low as 1.2 × 10 -3 Ω cm and transmittance > 80% in the visible range were obtained for 72-nm thick films. Finally, the first application of ALD-TZO as TCO was reported. TZO films were successfully implemented as top electrodes in silicon nanowire solar cells. The unique properties of TZO combined with conformal coverage realized by ALD technique make it possible for the cell to show almost flat EQE response, surpassing the bell-like EQE curve seen in devices with sputtered ITO top electrode.

Recent Advances in Materials Design Using Atomic Layer Deposition for Energy Applications

“…Ti‐doped ZnO grown by ALD provided sufficiently low contact resistance and was successfully applied as front transparent conductive oxide layer for the radial junction p‐type doped Si NW solar cells. [ 93 ]…”

Improvement of carrier collection in Si/a-Si:H nanowire solar cells by using hybrid ITO/silver nanowires contacts

“…We note that for sparser arrays of core/shell NWs, the minimal thickness of sputtered ITO needed for a continuous layer is lower [51], in which case the high optical transparency of the contact can be maintained without compromising the resistance. For dense NW arrays, instead of sputtering, deposition techniques enabling a more conformal growth such as atomic layer deposition (ALD) can be used [52]. Nonetheless, the total path that a charge carrier has to follow with an ideally conformal contact would still be much longer than the topto-top distance (ca.…”

Remarkable Thermal Conductivity Reduction of Silicon Nanowires during the Bending Process

“…Silicon nanowires (SiNWs) have been considered as competitive building blocks for various applications, such as thermoelectric generators, − solar cells, − battery anode, − chemical and biological sensors, − microelectromechanical systems, , and transistors, − due to their unique structure and remarkable electrical, optical, and thermophysical properties. Especially, SiNWs are ideal candidates for soft and flexible electronics, owing to their excellent bendable characteristics, which benefit from the one-dimensional geometry. − For the high performance and reliability of flexible electronic devices, such as thermoelectric generators and electronic chips, thermal management of the device is crucially important.…”