Large area and stable Perovskite-Silicon tandem solar cells: a modular approach

Conversion of solar energy into electricity is the fastest growing renewable energy source, and even going beyond any predictions. The steadily increasing efficiency of solar panels, faster production process and performance reliability are the driving factors for this growth. This is good news for the transition towards a fossil fuel free future. However, these solar panels that are implemented now (mainly Si) are reaching their maximum efficiency and for further improvements new concepts are required. Of the various options to increase the efficiency of solar cells further, tandem solar cells seem to be the most promising to become the next generation solar cell technology. In tandem devices, the light of the broad solar spectrum is converted by two solar cells that are stacked on top of each other. This reduces heat losses, while maintaining high voltage and current generation.

The rapid development of perovskite (PSK) materials with high band gap (> 1.6 eV) has resulted in a booming interest in this tandem technology. When a PSK based top cell is combined with a Si bottom cell, tandem cells are being developed using cheap and highly efficient photovoltaic materials. The efficiency of PSK-Si tandem solar cells is rapidly increasing and almost every year a world record is being broken. At this stage the record is at 33.9%, achieved by the Chinese company LONGi, while the Si single junction solar cell has reached an efficiency just below 27%. Thus, very high efficiencies are achieved with PSK-Si tandem solar cells. However, there are still quite some challenges to overcome of which stable performance, scalable deposition techniques and suitable deposition temperature on textured Si are among the most important ones. At this stage the high efficiencies are often achieved by deposition methods that are not scalable or on flat Si solar cells that limits the light absorption.

In this project we will introduce a novel PSK-Si solar cell using modular approach without compromising the efficiency. This modular approach implies that the top and bottom cells will be developed separately and connected afterwards. This eliminates the deposition on textured Si and the temperature constraints set by the bottom cell. Also, only scalable deposition techniques will be used to make the top and bottom cells.

The semi-transparent PSK top cell with a band gap higher than 1.67 eV will be developed using scalable deposition techniques such as evaporation and sputtering. The aim is to make large area stable PSK top cell that can cover a full Si wafer. Connection with the textured Si bottom cells can be done using transparent conductive adhesive or mechanical pressure and metal grids and needs to be investigated. The PSK single junction solar cells and tandem solar cells will be encapsulated and tested for stability. Standard JV, EQE and dark measurement will be performed and reflection and transmission measurement of the top cell. Stability issues in the PSK single junction and tandem cell will be unraveled using PL, XPS, and Raman spectroscopy. Semi-finished devices can be prepared to analyze the interfaces.

The Ph.D. candidate will join imec’s PV technology group performing world-class research on advanced thin-film and wafer-based technologies at our state-of-the-art research facilities located at the Energyville Campus in Genk. The student will work in both the thin film (Pk top cell) as well the waferPV (Si bottom cell) team and has the potential to collaborate with industrial partners.