As a building material, glass brings in the light and scenery from the outside while enclosing the space as a shelter. Less artificial lighting is needed and that reflects on your energy bill. With the invention of semi-transparent solar cells, the sunlight that falls on your windows can actually generate electricity and accrue further savings. However, such solar cells are notorious for their poor efficiency and high cost, which stop them from being widely applied. This is no longer the case as Prof. Feng Yan of the Department of Applied Physics and his research team have developed semi-transparent perovskite solar cells with graphene electrodes, which are 70% more efficient in converting solar energy to electricity and 50% less expensive than existing options. Light can even be captured from both sides of the cells.
Perovskite vs silicone / thin film solar cells
Solar power is a renewable and eco-friendly energy source. Most solar cells in the market are either the first or second generation, that is crystalline silicon or thin-film solar cells. “Silicon solar cells have very high power conversion efficiency, but they are produced under high temperature with much wastage, accounting for their high cost of production. Silicon cells are opaque and does not let light pass through. Thin-film cells are cheaper and lighter in weight. But to make it semi-transparent, usually precious metal nanowires or carbon nanotubes (CNTs) are used as electrodes, so that they are also expensive,” said Prof. Yan.
Thus, Prof. Yan and his research team based their invention on the new generation solar cells with perovskite, a class of material that can be made much more cheaply and with fewer emissions than silicon. “Perovskite is also more efficient in absorbing light, so that it can be made a lot thinner than silicon to capture the same amount of sunlight. The thinner it is, the higher its transparency,” he said.
Graphene vs precious metal / CNTs electrodes
The key mission here is to bring the cost down and there are three ways to achieve that. First, the research team needed to find a cheaper transparent material to replace precious metals (such as gold or silver nanowires) or CNTs to act as electrodes. “In our perovskite solar cells, we use graphene as electrode, which is much cheaper than precious metal CNTs, yet with higher conductivity, transparency and durability,” said Prof. Yan.
Secondly, the production of conventional semi-transparent solar cells entails vacuum chamber, which limits the productivity and adds to the cost. On the other hand, layers of chemicals are coated on the new perovskite solar cells simply by applying solutions on the substrate at low temperature and under atmospheric pressure. According to Prof. Yan, “not only are the raw materials inexpensive, but also the facilities and equipment involved. We can even turn a big roll of film into a solar cell with regular roll-to-roll printers. It is way cheaper than existing options.”
Last but not least, conventional semi-transparent solar cells exhibit a low conversion efficiency. Only 7% of the solar energy can be captured and converted into electricity. From an investor’s point of view, the lower the conversion efficiency, the longer it takes for the investment to pay off. “Our new perovskite solar cells boast a higher conversion efficiency of 12%, meaning the payback period can be shortened by 70%,” explained Prof. Yan.
Prof. Yan’s semi-transparent perovskite solar cells with graphene electrodes end up costing 50% less than conventional semitransparent solar cells, and are expected to be a game changer in the photovoltaic industry. The project also won a gold medal in 2016 International Invention Innovation Competition in Canada (iCAN 2016).
