Modelling of advanced photovoltaic devices

To move to a low-carbon future and avoid the worst effects of anthropogenic climate change, continuing reductions in the cost of renewable energy are required. Advanced tandem photovoltaic devices have emerged as key to achieving improvements in the efficiency of solar panels.

Unlike traditional single-junction solar cells, which have one semiconductor material to absorb light, tandem solar cells consist of multiple semiconductor layers stacked on top of each other, each with a different bandgap. This allows them to absorb a wider portion of the sunlight which enables a much higher efficiency potential. Improvements in efficiency are crucial in reducing the price of solar electricity and will thus impact the deployment of this important renewable energy technology.

The aim of this project is to develop new simulation techniques with the potential to advance the understanding of tandem solar cell devices. In particular, new simulation models are required to overcome the drawbacks of conventional single-junction solar cells where only a one semiconductor is evaluated. This project will extend the current modelling formalisms to a tandem architecture that captures the complexity of charge flow and losses in multijunction solar cell architectures, as well as ionic processes inside perovskite absorbers. Developing device models for tandem solar cells is a complex task that requires a deep understanding of the underlying physics and materials involved. This includes information such as the electrical properties of the semiconductors, such as bandgap, carrier mobility, carrier lifetime, and absorption coefficients. Understanding how light interacts with the materials is also crucial. The developed models should account for the absorption and reflection of incident light at each layer of the tandem, as well as the generation and recombination of electron-hole pairs (energetic charge carriers). The models will incorporate the electrical behaviour of the device, including the formation of built-in electric fields, charge transport, and extraction of generated carriers. This often involves solving semiconductor transport equations like the drift-diffusion or continuity equations. Most importantly, the tandem solar cells involve multiple semiconductor layers, and the interfaces between these layers can significantly impact device performance. Models should account for interface states, charge recombination, and band alignment at these interfaces. For validation, this project will involve electrical and optical characterisation of perovskite-silicon manufactured by our project partners (Oxford Physics and Oxford Photovoltaics), which can then be used to inform the development of finite element-based computer models to understand and optimise tandem solar cell devices. Overall, this work can impact the development of next-generation silicon-based photovoltaics and reduce the cost of solar energy.

This project falls within the EPSRC Energy Solar Technology and Optoelectronic Devices and Circuits research areas.