Developing Copper Bismuth Iodide Light Harvesters for Indoor Photovoltaics

The Internet of Things (IoT) is a network of autonomous, interconnected devices that are becoming increasingly present in both commercial and domestic settings. The IoT is growing exponentially, with IHS Markit forecasting that there will be 125 billion interconnected IoT devices by 2030. These devices are designed to perform specific functions and are connected in a wireless ecosystem allowing for information sharing between devices.
Currently, wireless IoT devices are largely powered by batteries. However, these batteries have a finite lifespan which places limitations onto the size and power of these devices, and adds a requirement on the user to maintain the device and regularly replace the battery. As the IoT rapidly grows, battery power alone may not be sustainable given the relative scarcity of materials that are used in batteries, an important example being lithium.
An alternative to IoT devices powered solely by batteries, is to harvest energy from 'freely available' sources. These ambient energy sources include light, mechanical vibrations, temperature gradients, and radiofrequency waves. Energy harvesters convert this ambient energy into electricity. The availability of ambient light in buildings is large in comparison to the availability of the other ambient sources. Consequently, indoor photovoltaic (IPV) energy harvesters, which convert indoor light to electricity, are developing as promising power sources for IoT devices.
These energy harvesting devices can recharge when building lights are on, allowing for IoT devices with long lifetimes. IPVs can act as the sole power source or can be used synergistically with an energy storage device, for example a battery. Supercapacitors have lower capacities than batteries but could be valuable energy storage systems in IoT devices as IPVs provide a regular power source. Furthermore, supercapacitors do not require the same restricted elements as batteries.
In recent years, Cu-Ag-Bi-I semiconductors have emerged as non-toxic, lead-free alternatives to lead halide perovskite photovoltaic (PV) materials. This DPhil project will investigate the potential of the compound Cu2BiI5 for application in IPVs.
To date, there have been no dedicated efforts to prepare high-quality thin films of Cu2BiI5 using nanocrystal synthesis. This project will develop an optimised synthesis route to Cu2BiI5 nanocrystal thin films through which control of size, shape, monodispersity and surface chemistry is achieved. These thin films will then be implemented into PV devices and their potential for application in IoT systems will be assessed. The fundamental photo-physical properties of Cu2BiI5 will be thoroughly investigated using high level optoelectronic characterisation techniques. A particular focus will be placed on understanding the charge-carrier behaviour and any limiting factors to charge-carrier transport.
This project aims to have a significant impact on the future of the IoT by developing IPV materials that can match or exceed the performance of the current industry standard. This project will expand the field of lead-free IPV materials by developing a synthesis route to high-quality Cu2BiI5 thin films and exploring their fundamental properties, with a particular focus on charge-carrier transport.
This project sits within three of the EPSCR Research Themes: Energy, Physical Sciences, and Information and Computational Technologies.