Application of photoreflectance to advanced multilayer structures for photovoltaics

TL;DR

This paper demonstrates the effectiveness of photoreflectance as a versatile, non-destructive diagnostic tool for analyzing advanced photovoltaic structures, revealing optoelectronic properties and interface characteristics crucial for PV device development.

Contribution

It presents experimental PR characterization of various advanced PV structures, highlighting its ability to analyze critical points, quantum confinement, electric fields, and oscillatory signals, thus promoting its use in PV research.

Findings

PR can identify absorption onsets and critical points.

PR distinguishes quantum confinement from delocalized states.

PR determines electric field intensities at interfaces.

Abstract

Photoreflectance (PR) is a convenient characterization tool able to reveal optoelectronic properties of semiconductor materials and structures. It is a simple non-destructive and contactless technique which can be used in air at room temperature. We will present experimental results of the characterization carried out by means of PR on different types of advanced photovoltaic (PV) structures, including quantum-dot-based prototypes of intermediate band solar cells, quantum-well structures, highly mismatched alloys, and III-V-based multi-junction devices, thereby demonstrating the suitability of PR as a powerful diagnostic tool. Examples will be given to illustrate the value of this spectroscopic technique for PV including (i) the analysis of the PR spectra in search of critical points associated to absorption onsets; (ii) distinguishing signatures related to quantum confinement from those originating from delocalized band states; (iii) determining the intensity of the electric field related to built-in potentials at interfaces according to the Franz-Keldysh (FK) theory; and (v) determining the nature of different oscillatory PR signals among those ascribed to FK-oscillations, interferometric and photorefractive effects. The aim is to attract the interest of researchers in the field of PV to modulation spectroscopies, as they can be helpful in the analysis of their devices.