Passivation of boron-doped р+-Si emitters in the (p+nn+)Si solar cell structure with AlOx grown by ultrasonic spray pyrolysis

Abstract

AlOx/(p+nn+)Cz–Si/IFO and ITO/AlOx/(p+nn+)Cz–Si/IFO solar cell structures have been fabricated from n-type Czochralski (Cz) silicon wafers through boron and phosphorus diffusion for producing the p+-Si emitter and n+-Si layer, respectively. The In2O3:F (IFO), AlOx, and In2O3:Sn (ITO) films have been grown by ultrasonic spray pyrolysis at 475°С, 330°С, and 375°С, respectively. The AlOx film thickness was varied in the range 27–108nm, the annealing time at 330°С in an Ar+5% O2 atmosphere containing vapor of a 2M H2O solution in methanol – in the range 0–18min, and the sheet resistance of the p+-Si emitter – in the range 28–133Ω/□ (varied through layer-by-layer chemical etching). We have studied the internal quantum efficiency (IQE) spectrum, photocurrent JIQE of the structures (evaluated from the IQE spectrum), as well as their photovoltage and pseudo-fill factor evaluated from Suns–Voc measurements. The results demonstrate that the level of p+-Si surface passivation increases with increasing AlOx film thickness and as a result of annealing. The optimal sheet resistance of the emitter is ∼65Ω/□. The pseudo-efficiency of the optimized ITO/AlOx/(p+nn+)Cz–Si/IFO structures was 20.2% under front illumination.