Development of HfOx-based anti-reflection and passivation layers for crystalline silicon solar cells applications

In this study, Hafnium oxide (HfO2) based thin films were produced by using spincoating method and then their antireflection behavior and passivation effects were investigated. First, samples were annealed at 500 ºC-1000 ºC temperature range in order to observe the effect of annealing temperature on coating of hafnium oxide on c-Si. According to XRD results, it was observed that the samples annealed at temperature above 500 ºC were crystallized as monoclinic phase. After annealing at 700 ºC, 10.87% reflection acquired for 71.3 nm thick HfO2 thin film as a result of reflection measurements. Furthermore, from ellipsometer measurements it was clearly observed that samples have 1.934 refractive index at 600 nm wavelength and refractive index increased to 2.05 by increasing annealing temperature to 800 ºC. After that, SiO2-thin film optimization was carried out to produce double layered and HfO2-SiO2 mixture thin films. HfO2-SiO2(1:1) thin films were produced and their antireflective and passivation effects were investigated. Minimum and average reflection values of HfO2-SiO2(1:1) thin films were obtained as 4.30% and 14.68%, respectively. Effective carrier lifetime of HfO2-SiO2(1:1) thin films after annealing at 600ºC increased to 32 μs compared to un-coated silicon effective carrier lifetime which is 2 μs. For higher annealing temperatures, it has been seen that the effective carrier lifetime decreases dramatically (for annealing temperatures of 700ºC and 800ºC, effective carrier lifetime decreases to 8.9 μs and 0.6 μs, respectively). Finally, after application of average experimental reflection values as anti-reflection coating (ARC) by using Afors-Het software to c-Si gelar cells, power conversion efficiencies (PCE) of solar cell without anti-reflection coating and high molarity (0.4M) HfO2 coated solar cell were determined as 11.68% and 17.58%, respectively. As a result of increments in the short circuit current density (Jsc) from 20.87 mA/cm2 to 31.27 mA/cm2 and in open circiut voltage (Voc) from 685.10 mV to 696.10 mV, 6% efficiency increase obtained for high molarity HfO2 thin film coated solar cell.