Enhanced energy conversion performance of silicon solar cells by quantum-confinement effect of polysilicon oxide

We propose a highly transparent polysilicon oxide (poly-SiO_x)/crystalline silicon (c-Si) front passivation contact (poly-SiO_x/c-Si) to overcome the parasitic current drawback and enhance the stability of silicon heterojunction (SHJ) solar cells. Poly-SiO_x has a mixed-phase crystalline structure with large crystalline grains embedded in a wide-gap amorphous silicon oxide (a-SiO_x) matrix, resulting in a quantum confinement effect. While the large crystalline phase facilitates dopant activation toward high conductivity (elevated Fermi level), resulting in substantial band bending at the c-Si/poly-SiO_x interface for additional field-effect passivation, the a-SiO_x matrix allows additional chemical surface passivation. Thus, passivation quality with an implied open-circuit voltage of 732 mV and a recombination current density of 4.3 fA/cm² was achieved. Owing to the interaction between the quantum confinement effect and the wide-gap a-SiO_x phase, the mixed-phase structure had a wide bandgap (1.98 eV), significantly increasing the absorption of the device in the short-wavelength region (≤500 nm). A hybrid rear-emitter SHJ solar cell using poly-SiO_x/c-Si achieved an efficiency of 23.95% with V_oc = 723 mV, a short-circuit current density of 40.9 mA/cm², and a fill factor of 81%.