Co-diffusion of boron and phosphorus for ultra-thin crystalline silicon solar cells

This paper reports the fabrication of crystalline silicon passivated emitter rear totally diffused (c-Si PERT) solar cells with ultra-thin p-type wafers 50 μm in thickness. Co-diffusion of boron and phosphorus in a single rapid thermal processing cycle, and an Al spin-on glass post-curing process were developed to remove the boron rich layer which is detrimental to c-Si solar cells. Co-diffusion was carried out with spin-on diffusion sources using boric acid and a P spin on dopant for simple and cost-effective emitter and back surface field (BSF) formation processes. The fabricated ultra-thin c-Si PERT cell featured an open circuit voltage (V_oc) of 0.575 V, a short circuit current density (J_sc) of 35.8 mA cm^-2, a fill factor of 0.725, and a power conversion efficiency of 15.0%. The efficiency has improved by 2% compared with the standard structure cell with Al-BSF using thin evaporated Al 2 μm in thickness. Along with cell output parameters, the flexural strength and critical bending radius were measured by a four point bending test, and the results showed that the solar cells with thinner rear Al electrodes are more applicable for a flexible solar cell device.