Characterisation, Spectroscopy, Imaging and Modelling (PP2.5)
PP2.5 Characterisation, Spectroscopy, Imaging and Modelling
Aims and objectives
This research theme aims to develop advanced modelling, reliable measurement and analysis techniques to extract the key optoelectronic properties of emerging photovoltaic materials and devices. These techniques aim to be applicable across various emerging technologies, device structures and sizes, absorber compositions, fabrication steps, and during device operation.
The full potential of photovoltaic devices is restricted by optical and electrical losses both in the starting materials and during their fabrication. Most emerging photovoltaic technologies are still far from their theoretical limits, and all require improvements in stability to improve payback.
Successful commercial applications will require further increases in efficiency and size, as well as improvements in durability to meet rigorous criteria of outdoor testing and scale-up. However, optimising and characterising these devices still requires further effort.
Emerging photovoltaic devices consist of a number of layers and interfaces, which can have very different physical and optoelectronic properties, and that can be altered significantly after each processing step. Interrogation of the changes are often difficult for the buried interfaces and layers in complete or partly finished devices. Second, if a finished device performs poorly, it is important to be able to pinpoint the origin (loss mechanism and location – depth and lateral position) of the problem. It is impractical to physically separate the materials after device fabrication, so it is necessary to have methods to either model or accurately determine the material and interface properties in-situ, or at multiple steps during the fabrication process. Furthermore, as the size of the photovoltaic sub-modules increases, the uniformity across the active layers becomes increasingly significant. Therefore, quantiﬁcation of the spatial distribution of these key cell parameters during device fabrication and afterward becomes increasingly important in predicting ultimate device performance and tracking process homogeneity.
This work package aims to solve these challenges by developing an integrated class of spectroscopy, imaging, and mapping techniques for spatial characterisation of the emerging photovoltaic materials and devices of any size (from microstructures to full-size devices). These techniques will be equipped with supporting numerical models to extract the key parameters, and also include the modelling of the film deposition process. We will introduce new tool sets to improve the processing and stability studies by monitoring spatially resolved optoelectronic properties of the devices during fabrication, under different degradation tests, and for various applications. The tasks will be achieved by leveraging the state-of-the-art characterisation facilities and expertise established across the ACAP nodes.
Research Activities and Plans
This work package will develop a range of innovative spectroscopies, imaging, and modelling techniques, as well as the foundation knowledge to interpret the experimental characterisation measurements of emerging solar cells. This will allow the unambiguous separation of the effects of the electrical and optical properties of materials and defects, and investigate their correlations with efficiency losses, hence providing thorough insights into complex loss mechanisms. This will help to identify root causes of the losses and engineer fabrication processes and materials to mitigate them. This will be achieved through activities across several key activities:
PP2.5.1 Advanced Spectroscopy
Understanding the electrical, optical and structural properties will unlock fundamental fingerprints of new materials. This will involve developing and harness key spectroscopic tools that are:
Light-based (Photoluminescence (PL), time resolved PL, Raman, reflection and absorption spectroscopy): bandgap, absorption, parasitic losses, recombination, minority carrier traps.
Electron beam-based (UV and X-Ray photoelectron and energy dispersive X-Ray spectroscopy (UPS, XPS and EDS)): composition, energy levels, work functions.
X-ray and neutron scattering to determine films densities and interface structures.
PP 2.5.2 Imaging and Microscopy
The link between the nanoscale and microscale material properties to the macroscale device performance will be achieved through the following approaches:
Scanning and Transmission electron microscopy:
Luminescence imaging (PL, electroluminescence (EL), cathodoluminescence): Quasi Fermi level splitting, ideality factor, pseudo-IV, activation energy, Urbach energy, series resistance, etc.
Dark lock-in thermography: detection of shunt and damaged p-n junctions
Light- and electron-beam induced current microscopy
PP 2.5.3 Advanced Photovoltaic Modelling
Advanced models and simulation of photovoltaics are critical to (i) support the development of new materials and device architectures, and (ii) provide an understanding of the underlying operation of real devices based on a comparison to extracted material and device parameters.
To achieve this, we will focus on developing:
Advanced 1D, 2D and 3D photovoltaic simulation tools that can be applied to emerging photovoltaics of varying device architecture
Machine learning approaches to accelerate the optimisation of devices and the regression between simulated and experimentally tested devices.
Methodologies to predict and optimise PV module performance.
Methods for simulating the deposition of materials and subsequent film morphology and the effects on the photophysical and charge transport properties.
Investigators: Dr Hieu Nguyen (ANU), Dr Ziv Hameirity (UNSW), Prof. Thomas White (ANU), Prof. Jacek Jasieniak (Monash), Prof. Paul Burn and Dr Paul Shaw (UQ).