Development of boron-doped poly-SiCx for TOPCon solar cells

Passivated contacts based on p-type polycrystalline silicon carbide (poly-SiC x ) on tunnel oxide are promising for achieving excellent carrier selectivity and enhanced thermal stability in TOPCon solar cells. In this work, we develop and investigate the structural and electrical properties of p-type poly-SiC x /SiO x . The poly-SiC x layers were formed from boron-doped a-SiC x layer deposited by relatively low-temperature PECVD on wet-chemically grown SiO x on chemically polished wafers. Following high-temperature annealing at various temperatures and intervals, an AlO x /SiN x /AlO x hydrogenation stack was symmetrically deposited. Finally, the test structures were subjected to fast firing at different peak temperatures. A representative passivation response was obtained for the 70 nm SiC x /SiO x contact crystallized at 850 °C and subsequently firing at 900 °C with an iV oc of 700 mV and a J 0 of 9 fA/cm 2 . FTIR spectra revealed the disappearance of Si–H stretching bands around 2000–2100 cm −1 and C–H-related features near 2900 cm −1 after crystallization, confirming hydrogen effusion. ECV measurements of the crystallized samples showed an active boron concentration of ∼1 × 10 20 cm −3 and a consistent dopant profile throughout the layer, confirming effective boron dopant activation. Numerical simulations further demonstrate the potential of the optimized p-type poly-SiC x /SiO x contact in a front- and back-contacted TOPCon cell configuration, where the p-type poly-SiC x contact is locally implemented beneath the front-side metal contacts, yielding a simulated conversion efficiency ≥25%.