Recycling Perovskite Solar Cells

Recycling Perovskite Solar Cells

By Judy Tsao, Member-at-Large for the GCI

Solar energy is arguably the most abundant and environmentally friendly source of energy that we have access to. In fact, crystalline silicon solar cells have been employed in parts of the world at a comparable cost to the price of electricity derived from fossil fuels.1 The large-scale employment of solar cells, however, remains challenging as the efficiency of existing solar cells still needs to be improved significantly.

An important recent breakthrough the field of solar cells is the use of perovskite solar cells (PSC), which includes a perovskite-structured compound as the light-harvesting layer in the device (Figure 1). Perovskite is a name given to describe the specific 3-D arrangement of atoms in such materials. Even though the first PSC was reported only in 2009, its power conversion efficiency (PCE) has already been reported to exceed 20%, a milestone in the development of any new solar cells which typically takes decades of optimization to achieve.2

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Figure 1. Thin-film perovskite solar cell manufactured by vapour deposition (photo credit: Boshu Zhang, Wong Choon, Lim Glenn & Mingzhen Liu)

PSC has several advantages compared with traditional solar cells, including low weight, flexibility, and low cost.3 There are, however, several challenges that must be overcome before PSC can be brought to the market. The most common PSC to date includes CH3NH3PbI3 and related materials, which contain soluble lead (II) salts that are toxic and strictly regulated.

Interestingly, there has been a consensus in the literature that the lead content in the perovskite layer is not actually the main issue in the environmental impact of PSC production.4 Part of the reason for this conclusion is simply that the thickness of perovskite layer required would amount to less than 1000 mg of lead in one square meter of material. This value is only modest compared to lead pollution from other human sources such as lead paints or lead batteries.5

The main environmental concerns regarding PSCs appear to lie in the use of gold and high temperature processes during the manufacturing of the devices.6 It has thus been suggested that, in order to reduce the environmental impact of PSCs, recycling of raw materials is very important. In a recent study by Kadro et al., 7 a facile protocol for the recycling of perovskite solar cell was developed. The entire procedure takes place at room temperature and takes less than 10 minutes (Figure 2).

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Figure 2. Schematic process for recycling PSC components [7].

As it turns out, components of a fully assembled PSC can be extracted by sequentially placing the device in different solvents. Step 1 of the procedure uses chlorobenzene to remove the gold layer, while step two uses ethanol to dissolve CH3NH3I. This then leaves PbI2 to be the only component remaining on the device, which can be removed by just a few drops of N,N-dimethylformamide. It is also worth noting that the recycled materials can be fabricated into a complete PSC again without significant drop in performance.

Even though the discovery of PSC has only been made less than a decade ago, its potential in applications in photovoltaics has been underlined by numerous studies. It is especially gratifying to see that the environmental impacts of such devices are already under active research before PSCs are introduced to the market. While these studies have demonstrated that PSCs have low environmental impacts when properly recycled, there are other challenges still facing researchers in this field. In particular, the short lifetime of such devices needs to be improved to match that of traditional silicon-based solar cells. Nevertheless, the facile method of recycling PSCs without compromising the performance will certainly make them even more competitive than traditional solar cells.

References:

  1. Branker, K. et al. Renewable Sustainable Energy Rev. 2011, 15, 4470.
  2. Yang, W. S. et al. Science, 2015, 348, 1234.
  3. Snaith, H. J. Phys. Chem. Lett. 2013, 4, 3623.
  4. Serrano-Lujan, L. et al. Energy Mater. 2015, 5, 150119.
  5. Dabini, D. Phys., 2015, 6, 3546.
  6. Espinosa, N. et al. Adv. Energy Mater. 2015, 5, 1.
  7. Kadro, J. M. et al. Energy, Environ. Sci. 2016, 9, 3172.

 

Iceland is Greener Than You Think

By Peter Mirtchev, Member-at-Large for the GCI

This past summer I had the opportunity to travel to Iceland as part of the Global Renewable Energy Education Network’s (GREEN) 10-day program in Renewable Energy & Sustainability. GREEN organizes educational adventure workshops in a number of unique locations including Iceland, Costa Rica, and Peru. The trips are focused on a central theme such as Renewable Energy or Water Resource Management, and are open to undergraduate and graduate students from around the world through a competitive application process. The registration fees cover all expenses except the flight and even though the cost might be steep for a student budget, there are plenty of funding opportunities to explore through your university’s financial office. Feel free to email the GCI if you’re interested and want to know more!

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Iceland is as interesting to learn about as it is beautiful to explore. And that’s a lot.

Iceland is an amazing place. The country is completely isolated on a volcanic island in the mid-Atlantic and has a population of just over 300,000 or about the same as a few large sports stadiums packed together. As such, it tends to lead the world in per capita categories; for example Iceland has the most tractors per acre of arable land, but the second least amount of actual arable land of all countries that practice agriculture. More relevantly, Iceland is a global leader in renewable energy, supplying approximately 80% of its total energy demand from renewable sources. The country has abundant geothermal and hydroelectric resources that are used for heating and electricity generation respectively. In fact, the only fossil fuel burned in Iceland is the gasoline used to power everyone’s cars!

A geothermal plant in Iceland.

As part of the program, our group got guided tours of two geothermal and hydroelectric power plants and two days of energy lectures from professors at Reykjavik University’s School of Energy. We were also invited to a reception by Iceland’s President, Olafur Grimsson, where we discussed global renewable energy policy and how we might be able to implement some of the lessons learned in Iceland when we return to our home countries. At the end of the program, we developed innovative Capstone Projects and got feedback on their feasibility. And that was only the educational aspect of the program! When not working, we took advantage of Iceland’s stunning natural beauty, doing everything from soaking in hot springs to hiking on glaciers.

I’d like to conclude by saying that I only became aware of this fascinating program by being part of the GCI. As we’ve become more established and started getting more recognition outside of U of T, we’ve received many new opportunities for our members to get involved in outside initiatives. This has helped us expand our knowledge of sustainability, and helped us professionally by introducing us to many new contacts. To students, this is hugely helpful and I encourage anyone with an interest in sustainability to get involved in any initiative that tries to lessen our impact on our planet.

And try to go to Iceland. You won’t regret it.