Chemical stoichiometry effect of hafnium oxide (HfOx) for passivation layer of PERC solar cells

Abstract

Hafnium oxide (HfOx) is being investigated as a new candidate for the passivation layer of silicon solar cells due to its excellent electrical and optical properties, such as high dielectric constant, large band gap, refractive index, high transparency, and thermodynamic stability in contact with Si. In this paper, the HfOx is analyzed for novel material applied to the passivation layer to improve the performance of passivated emitter and rear contact (PERC) solar cells. For optimisation of the passivation layer of the PERC solar cell, chemical stoichiometry and passivation properties such as interface trap density, fixed charge and effective carrier lifetime are studied before and after the annealing process. After annealing in O2, interface trap density (Dit) decreased from 8.15 × 1010 eV−1cm−2 to 2.37 × 1010 eV−1cm−2 and the fixed charge (Qf) changed from positive to negative after annealing due to the reduction of oxygen vacancies. However, the passivation properties did not meet expectations due to blistering after annealing at 500 °C or higher and the highest effective carrier lifetime was 188.56 μs after annealing at 400 °C, which was improved from 49.48 μs before annealing. It was confirmed that improved passivation performance and solar cell efficiency could be achieved through the chemical stoichiometry effect by a simple annealing process.