Boron‐doped polysilicon using spin‐on doping for high‐efficiency both‐side passivating contact silicon solar cells. (16th November 2022) - Park, HyunJung
Abstract: This study focuses on boron‐doped p + polysilicon (poly‐Si) passivating contacts using spin‐on doping (SOD). Experimental conditions, including annealing conditions, SOD concentration, and poly‐Si thickness, were controlled to improve passivation. Based on the analysis results, the passivation quality mainly changes with indiffusion and doping concentration, causing Auger recombination and field effects. Meanwhile, grain size also influences the passivation quality but showed marginal characteristics. Through further optimization using an etch back and diffusion barrier, the efficiency of the flat reference solar cell was improved to 17.5% with an open‐circuit voltage of 695 mV using a p + poly‐Si contact emitter, the highest reported efficiency using SOD on saw‐damage‐etched surfaces. This study includes a detailed analysis of SOD p + poly‐Si and shows promising results with potential for application in tandem devices. Furthermore, the cell efficiency is expected to increase by controlling the doping profile and application of textured surfaces, selective emitters, and forming gas annealing (FGA). Abstract : The passivation quality of the p + poly‐Si passivating contacts with boron SOD was investigated. The factors influencing the passivation quality of p + poly‐Si are crystallinity, indiffusion, and doping concentration. A 17.5% efficiency with 695 mV V O C was achieved by controlling the process parameters with optimization and simulation, reaching the highest reported cell efficiency with SOD p + poly‐Si on saw‐damage‐etched flat surfaces. Highlights: The passivation quality of p + poly‐Si passivating contacts with boron SOD was investigated. The factors influencing the passivation quality of p + poly‐Si were crystallinity (grain size), indiffusion of boron into the bulk, and doping concentration (field effect). The doping process was further optimized by controlling the boron indiffusion from the SOD source to c‐Si bulk using an additional diffusion barrier layer that controls the boron doping profile. Poly‐Si contact cells with both‐side flat surfaces and poly‐Si contacts showed a maximum efficiency of 17.5% with V O C of 695 mV when a developed p + poly‐Si was applied at the front. This is the highest reported efficiency using boron SOD‐doped p + poly‐Si emitter on saw‐damage‐etched flat surfaces. Based on a wide range of analyses and experimental results, a 3D energy band diagram of p + poly‐Si/SiO x /c‐Si passivating contacts is exhibited. The cell result validates its potential for use in silicon‐based tandem solar cells and the efficiency can be further improved by applying textured surfaces, FGA, and selective emitter for improved metal contacts.