Abstract
Recently, titanium oxide has been widely investigated as a carrier-selective contact material for silicon solar cells. Herein, titanium oxide films were fabricated via simple deposition methods involving thermal evaporation and oxidation. This study focuses on characterizing an electron-selective passivated contact layer with this oxidized method. Subsequently, the SiO2/TiO2 stack was examined using high-resolution transmission electron microscopy. The phase and chemical composition of the titanium oxide films were analyzed using X-ray diffraction and X-ray photoelectron spectroscopy, respectively. The passivation quality of each layer was confirmed by measuring the carrier lifetime using quasi-steady-state photoconductance, providing an implied open circuit voltage of 644 mV. UV–vis spectroscopy and UV photoelectron spectroscopy analyses demonstrated the band alignment and carrier selectivity of the TiO2 layers. Band offsets of ~0.33 and ~2.6 eV relative to the conduction and valence bands, respectively, were confirmed for titanium oxide and the silicon interface.
Highlights
Most of the commercial solar cell market is based on crystalline silicon wafers
A maximum implied Voc of 690 mV was achieved with a 5 nm TiO2 layer after forming gas annealing (FGA) at 350 ◦ C for 3 min. This value is excellent and is comparable with those of high-efficiency titanium oxide electron-selective contact solar cells fabricated by other groups using atomic layer deposition (ALD) [26]
Electron-selective titanium oxide films were formed via thermal eVaporation and subsequent annealing with oxygen
Summary
Most of the commercial solar cell market is based on crystalline silicon wafers. Approximately90% of the total silicon produced annually is employed in the photovoltaic (PV) industry. Most of the commercial solar cell market is based on crystalline silicon wafers. As the dopant concentration increases, the electrons and holes can be separated effectively; there are some limitations to the manufacture of high-efficiency solar cells. It has been reported that Shockley–Read–Hall (SRH) recombination resulting from dopant complexes reduces the Voc [1,2,3]. For these reasons, substrate doping-free solar cells have been actively studied, and record efficiency has been achieved with a crystalline cell based on heterojunction technology using intrinsic amorphous silicon (HIT) [4].
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