A Kinetic Monte Carlo approach to study transport in amorphous silicon/crystalline silicon HIT cells

Abstract

The photogenerated carriers in a-Si/c-Si HIT cells must traverse the intrinsic amorphous silicon barrier in order to be collected. As this barrier region is amorphous in nature, it contains many defect states, and thus carrier transport is mainly described by defect assisted transport. The present work applies the Kinetic Monte Carlo (KMC) method for the defect assisted transport by analyzing the interactions between discrete defects and discrete carriers. We explore the `hopping' nature of transport via defects by considering the effect of phonons. The addition of phonons allows us to study non-iso-energetic transitions for injection and extraction of carriers. Once the carriers `hop' through the barrier, they are extracted by three main mechanisms, namely, thermionic emission, Poole-Frenkel emission and phonon assisted defect emission. Simulations indicate that Poole-Frenkel emission and thermionic emission are negligible whereas emission of carriers via phonon assisted hopping is the dominant mode of extraction. The effect of different defect distributions on transport is also analyzed.