| Pacific Rim Symposium on Surfaces, Coatings and Interfaces (PacSurf 2016) | |
| Energy Harvesting & Storage | Tuesday Sessions |
| Session EH-TuM |
| Session: | Surfaces & Interfaces for Solar Cells and Solar Fuels |
| Presenter: | Sebastian Siol, NREL, USA |
| Authors: | S. Siol, NREL, USA P. Schulz, NREL, USA M. Young, NREL, USA K. Borup, NREL, USA G. Teeter, NREL, USA A. Zakutayev, NREL, USA |
| Correspondent: | Click to Email |
Energy band alignments at heterointerfaces play a crucial role in defining the functionality of semiconductor devices. The search for material systems with suitable electronic band alignments is one of the key challenges in developing novel photovoltaic technologies. Particularly the tuning of band offsets has enabled significant advances in efficiency for several state of the art thin film solar cell technologies. While the theoretical prediction of band alignments at semiconductor heterointerfaces is often very limited, interface experiments utilizing X-ray photoelectron spectroscopy (XPS) measurements can be employed to track the evolution of the electronic structure at the interface. In particular the V-IV binary chalcogenide Sb2Se3 has been identified as a prospective absorber material for the next generation of thin film solar cells [1], yet the understanding of interfacing this compound semiconductor to commonly employed buffer layers such as ZnS is still in its very infancy.
In recent years high throughput, combinatorial materials science methodology has gained tremendous interest [2]. In this work we demonstrate how combinatorial techniques can be utilized to increase the throughput of in-situ experiments to investigate the interface formation for respective semiconductor heterojunctions. Thin films are grown with intentional thickness gradients on the substrate, to minimize the required number of depositions and transfers. In addition, other deposition parameters such as the deposition temperature or composition can be systematically co-varied with thickness to cover several individual interface experiments on one substrate.
Using orthogonal thickness and temperature gradients a combinatorial in-situ interface experiment was set up, that provided a comprehensive dataset for the extensive investigation of the band alignment at the prototypical Sb2Se3/ZnS heterojunction. Our findings point to a large conduction band offset of ΔECB= 1.75 ±0.05 eV along with a potentially detrimental interfacial reaction at the junction. With this result, the study reveals why the choice of a ZnS buffer layer would limit device parameters and gives initial guidelines for alternative buffer layer materials with smaller electron affinities.
The method presented in this contribution can easily be applied for other material systems and will enable other researchers to quickly acquire comprehensive data for a more accurate picture of electronic processes across potential device interfaces.
[1] Y. Zhou et al. Nat. Photonics 2015, 9, 409.
[2] M. L. Green et al. J. Appl. Phys. 2013, 113, 231101.