Role of hot carriers in the interfacial transport in amorphous silicon/crystalline silicon heterostructure solar cells

Abstract

The transport of photogenerated minority carriers (photocarriers) across the heterointerface of amorphous silicon (a‐Si) and crystalline silicon (c‐Si) in a‐Si/c‐Si heterostructure solar cell is shown in this work to critically depend on the non‐Maxwellian energy distribution function (EDF) of those carriers impinging on the heterointerface. A theoretical model is presented that integrates the effect of the high electric field inversion region upon EDF of the impinging carriers with the transmission probability of those carriers across the heterointerface. The transport of the photocarriers across the high electric field inversion region is simulated by the full solution of the Boltzmann transport equation by Monte Carlo (MC) technique while the transmission probability of carriers across the heterointerface is calculated through the percolation path technique. The results are discussed under two different condition of band bending; strongly inverted and weakly inverted c‐Si surface. The results comparing different conditions of band bending show that the energy distribution of the carriers impinging on the heterointerface is non‐Maxwellian and the integrated photocarrier collection increases with the strength of the inversion field since the carrier population is weighted toward higher energy where the transmission probability through the barrier is higher. Thus, we demonstrate that hot carriers play an important role in heterostructure cell operation.

Correlated Nonideal Effects of Dark and Light I–V Characteristics in a-Si/c-Si Heterojunction Solar Cells

“…Indeed, several experimental reports (e.g., [16]- [19]) have suggested a link between the properties of a-Si and the occurrence of a nonideal "S-type" curve under certain circumstances. Furthermore, numerical modeling was used to understand the transport mechanism under light, using tunneling across the a-Si/c-Si interface and drift-diffusionbased transport [20], as well as hot-carrier-based transport [21]. These studies were mainly confined to understanding the light I-V properties, with no specific effort to correlate the features to the dark I-V.…”

A kinetic Monte Carlo study of defect assisted transport in silicon heterojunction solar cells

“…The characteristic decay energy is traditionally found to be 45 meV in literature (see Ref. [4]). But by varying the decay energy from 5 meV-100 meV it is possible to generate defect densities of 10 18 cm -3 to 10 20 cm -3 .…”

“…1) together create an unconventional situation where assumptions made by the conventional drift diffusion model are no longer valid. Previous work by Ghosh et al [4] has shown the effect of high fields on the carrier distribution at the heterointerface. In this work we explore and study the various mechanisms that govern transport of photogenerated carriers in the intrinsic amorphous silicon barrier.…”

Multiscale modeling of silicon heterojunction solar cells

“…Previously, Ghosh et al [53] used ensemble Monte Carlo (EMC) simulations to investigate the effect of high electric fields on photogenerated holes at the a-Si:H(i)/c-Si heterointerface using a single band model. In this chapter, an in-house EMC solver is presented which extends the EMC approach developed by Ghosh et al to model high field effects.…”