Crystalline silicon remains the predominant bulk material for the fabrication of photovoltaic cells, but progress is proceeding with other materials, which may offer certain benefits. Organic solar cells offer the possibility for price reduction, and they can be mechanically flexible. And solar cells made of organometal halide perovskites offer the possibility of significant efficiency improvements beyond the 20% or so offered by crystalline silicon implementations.
With respect to organic solar cells, imec recently described the development of fullerene-free organic photovoltaic (OPV) multilayer stacks, claiming a record conversion efficiency of 8.4%. This breakthrough achievement, the organization said, is an important step to bring organic photovoltaic cells to a higher level in the competitive thin-film photovoltaics marketplace.
According to imec, organic solar cells are an interesting thin-film photovoltaic technology due to their compatibility with flexible substrates, but further enhancements are needed to make the production of organic photovoltaics more easily scalable into industrial production processes.
Imec presented its recent results in Nature Communications.
With respect to perovskites, Yanfa Yan, Wanjian Yin, and Tingting Shi of the University of Toledo in Ohio have published a paper titled “Unusual defect physics in CH3NH3PbI3 perovskite solar cell absorber” in Applied Physics Letters. “Thin-film solar cells based on methylammonium triiodideplumbate (CH3NH3PbI3) halide perovskites have recently shown remarkable performance,” they wrote.
Commenting on their work in Physics Today, Johanna L. Miller noted that the balance between cost and performance in solar-cell fabrication remains elusive, but solar cells based on perovskites “…have recently and rapidly emerged as one of the most promising contenders yet. Last year, just four years after the cells’ debut, two groups independently reported perovskite solar cells with power-conversion efficiencies of 15%.”
Challenges remain, she noted, including cell stability. The cells, she wrote, must be sealed to protect them from water, but the cells can leak, potentially introducing toxic lead into the environment. Some researchers, she concluded, are looking to replace the lead with tin.
Despite the challenges, perovskites remain promising. In the Guardian, Bernie Bulkin, who chaired the Office of Renewable Energy for the UK Government from 2010-2013 and is a member of the UK Sustainable Development Commission, wrote recently, “…perovskite PV is at the point of, perhaps, maximum optimism. There are predictions that the efficiencies could reach 50%, the costs could fall to well below where silicon might get to in 10 years, and the science points to it being desirable to make these cells thicker, rather than as thin films, meaning they can be suitable as window or roofing materials. And the prototype cells produced have partial transparency.”
Bulkin, who is also a director of Ludgate Investments Ltd. and of HMN Colmworth Ltd., concluded by noting that several companies are working to commercialize perovskite, including Oxford PV, which has attracted £2m of start-up funding.