Reduction of interface traps at the amorphous-silicon/crystalline-silicon interface by hydrogen and nitrogen annealing

摘要

We show a reduction in the interface trap density (D_(it)) at the amorphous-silicon/crystalline-silicon interface by annealing in nitrogen (95%) and hydrogen (5%) for 10, 20 and 25 min at 400 ℃. Fabricated a-Si(n~+)/c-Si(p)/c-Si(p~+) heterojunction solar cells were measured both in the dark and optically under 1 sun after annealing. The dark current reduces from ～9.5 × 10~(-4)mA/cm~2 at -0.5 V to ～3.02 × 10~(-5) mA/cm~2 after annealing for 25 min at 400 ℃. Under AM1.5G the open circuit voltage (V_(oc)) increases from 0.57 V to 0.62 V. The short circuit current density (J_(sc)) increases from 12.1 mA/cm~2 to 13.2 mA/cm~2 and the fill-factor (FF) increases from 61.18% to 68.07%. The efficiency increases from 4.28% to 5.55%. The peak External Quantum Efficiency (EQE) increases from 55% to 63%. In addition, the D_(it) profile at the a-Si/c-Si interface is modeled and simulated. Trap Assisted Tunneling (TAT) model along with electric field enhancement via the Poole Frenkel Effect is included as Electron-Hole-Pair (EHP) generation mechanisms. Combining the simulation and annealing results reveals a 90% reduction in D_(it) at the a-Si/c-Si interface.