Development of innovative nanostructured dielectric materials for interface passivation in thin film solar cells 

Project PTDC/FIS-MAC/29696/2017 funded by FCT (Portugal)

Photovoltaics is a technology with the potential to shift the worldwide energy industry from fossil fuels-based production to renewable energy. Furthermore, photovoltaics has seen an exceptional reduction of its production costs. In fact, installation costs are now on par with most conventional technologies, being cheaper than wind energy or coal energy in some locations. Such cost reduction has occurred mostly due to market gains and implementation of surface-passivation technology in silicon solar cells. This reduction has shown that only high performing and stable technologies will survive since the costs of the whole system are now more expensive than the module itself. In this project, our final goal is to introduce surface-passivation technology in thin film solar cells which will allow for the cost of thin film solar cells to become lower than the current silicon costs.

Thin film solar cells based in Cu(In,Ga)Se2, already have an electrical performance higher than those based on multi-crystalline silicon with power conversion efficiency numbers of 22.6 % versus 20. 8%. Moreover, this technology has many advantages: i) it can be produced in flexible substrates; ii) it is low-light sensing: iii) it has a significant lower energy payback for the fabrication of its modules; iv) it is superior and more stable than silicon when working in hot environments due to its positive coefficient of thermal behaviour (silicon is negative); and v) since it is produced using a monolithically integration, a single factory is capable of transforming a glass substrate into a solar module in less than two hours. All these factors allow for thin film solar modules to be produced already at a lower cost than silicon solar modules. However, there is a significant room for improvement as the solar cell structure of thin film solar cells has been the same since 1985 and comprises no interface passivation strategies. The introduction of such technology has the capability to increase the solar cell power conversion efficiency by 3.4 % (absolute). This development has been hindered mostly by the fact that up to now there are no capable techniques to evaluate and quantify surface recombination velocity. 

In this project we will develop an innovative technique based in muon spectroscopy with an unmatched capability of analysing interface defects. Despite the enormous competences that muon spectroscopy has shown in bulk semiconductors, it is still an unstudied technique in thin films. Hence, in the project we will deploy muon spectroscopy allowing us to identify the best passivation material and passivation strategies for thin film solar cells. This increased know-how will permit us to fabricate a prototype of a thin film solar cell with passivated interfaces with a superior electrical performance. The increase of the electrical performance leads to a significant reduction of production costs per watt opening the way to advance the photovoltaics market.