Surface passivation optimization with boron-doped polycrystalline silicon contacts on textured silicon for photovoltaic applications

Passivating contacts made of polycrystalline silicon (poly-Si) on top of a thin silicon oxide (SiO x ) have emerged as a key enabling technology for high-efficiency silicon solar cells, such as tunnel oxide passivated contact (TOPCon) devices. However, achieving high-quality surface passivation with hole selective poly-Si contacts remains challenging, especially on textured silicon. In this work, boron-doped p + -poly-Si contacts were formed on textured silicon surfaces using low pressure chemical vapor deposition (LPCVD) process, followed by ex-situ doping by BCl 3 diffusion. Particular attention was paid on engineering more thermally robust oxide layers and controlling the impact of the boron diffusion step on the oxide integrity. A combination of chemical (O 3 -based) and thermal oxidations, together with a boron diffusion process employing drive-in temperatures between 850 °C and 900 °C significantly improved the passivation quality and suppressed a central defect pattern seen with thermal oxidation only. Moreover, the impact of the poly-Si thickness on the surface passivation performance was studied. Poly-Si thicknesses ranging from 41 nm to 108 nm on textured samples resulted in comparable single surface emitter saturation current density (J 0E ) values, indicating a limited influence of the layer thickness within this range. As a result, high and uniform passivation quality was achieved on symmetrical p + -poly-Si textured samples, with a minimum J 0E of 20 fA.cm −2 and implied open-circuit voltage (iV OC ) values of up to 705 mV.