A novel passivating electron contact for high-performance silicon solar cells by ALD Al-doped TiO2

Titanium oxide (TiO2) thin film has attracted wide interest in high-efficiency silicon solar cells as an electron selective contact due to its low conduction band offset with silicon and an excellent level of passivation, while the incorporation of a small amount of dopants is also expected to improve the performance of thin films. In this work, assisted with density functional theory (DFT) modelling, we study the electronic band structure of aluminum (Al)-doped TiO2 (ATO). The atomic-layer-deposited (ALD) ATO thin films are successfully prepared, and the elemental analysis, passivation effect, thermal stability, conductivity and optical properties of the ATO are systematically investigated. An ultra-high effective minority carrier lifetime (tau(eff)) of 1.9 ms and a low contact resistivity (rho(c)) of 0.1 Omega.cm(2) are simultaneously achieved on silicon wafers. Meanwhile, it is found that the ATO thin films possess better thermal stability than the TiO2 thin film. Finally, a large-area (118.7 x 100 mm(2)) p-type passivated emitter and rear contact (PERC) solar cells integrated with an ALD ATO layer on the illumination side was fabricated, and a champion efficiency of 21.4% was achieved with an optimal Al concentration in ATO, which is significantly higher than a PERC solar cell with intrinsic TiO2. This work shows ATO a very attractive alternative achieving high-efficiency crystalline silicon solar cells.