More energy from the sun hits the Earth’s surface in an hour than humanity uses each year, making solar power the most promising candidate whenever the future of energy is discussed. The last 25 years transformed solar power from verified oddity to the world’s fastest-expanding energy source. While the photovoltaic (PV) market is still dominated by silicon solar panels, perovskite solar cells (PSCs) have been considered as a ‘gamechanger’ that can eke out more energy from the sun’s photons and be used more flexibly than today’s panels.

Making from the most abundant mineral on Earth, PSCs became the frontrunner among all emerging PV technologies. From humble beginnings in 2009 with an efficiency of 3.8% and lasted only minutes, the best PSCs now boast an efficiency of 23.3% and can work for thousands of hours under harsh test conditions.

Researchers from Huazhong University of Science and Technology, led by Han Hongwei, have recently reviewed the advances toward commercially viable PSCs and discussed challenges that remain. The work, which can be found on Science (http://science.sciencemag.org/content/361/6408/eaat8235), also include contributions from researchers around the world such as Edward H. Sargent at University of Toronto (Canada), Sang Il Seok at Ulsan National Institute of Science and Technology (Korea), and Michael D. McGehee at University of Colorado (USA).

Figure 1. Configurations and application demonstration of PSCs.

(A) PSCs have been developed in various device configurations, including mesoscopic, planar, triple mesoscopic and tandem structures.

(B) A 110 m² perovskite PV system with printable triple mesoscopic PSC modules (3600 cm² for each) was launched by WonderSolar in China.

PSCs can deliver excellent performance alone with device configurations include mesoscopic formal (n-i-p) and inverted (p-i-n) structures, planar formal and inverted structures, and the printable triple mesoscopic structures (shown in Figure 1A). They can also be combined with other existing mature PV technologies, making ‘tandems cells’, to deliver more power than either could manage alone. The notable improvement in both the PSC efficiency and stability in the past few years has helped underpin the rapid progress of single-junction PSCs as well as tandem cells. In particular, a 10,000 hours lifetime of printable triple mesoscopic PSCs was obtained last year, which equals to the total irradiation of ten years outdoor use in most of Europe, offering more reassurance for PSCs to enter the PV market.

WonderSolar in China announced its latest milestone: a perovskite PV system with printable triple mesoscopic PSC modules that exceeding a total area of 110 m² (shown in Figure 1B). The system is a testament to two crucial areas of progress in PSCs over the past few years: the devices longevity and their ability to upscale. Further studies of these increased-area modules and systems will expand to cover both fundamental topics on materials and lab-sized cells, and also studies to address issues of industrial-scale manufacturing and deployment.

WonderSolar isn’t the only commercial player in perovskite. Microquanta Semiconductor recently obtained the highest efficiency of rigid perovskite mini-module; Saule Technologies is working on flexible perovskite cells; a consortium that includes Greatcell Solar, Solliance, Oxford PV, Solaronix and Tandem PV is developing stand-alone and tandem cells; and several other companies are in the mix.  

Of course, there is no guarantee perovskite will succeed as solar’s new wonder material. The development is still at very early stages, both academic and companies still have technical and production challenges to overcome. This include industry-scale electronic-grade films, recycling methods to address concerns regarding lead toxicity, and the adoption of standardized testing protocols to predict the operation lifetime of PSCs. Modules will need to pass light-induced degradation, potential-induced degradation, partial shade stress, and mechanical shock. The field can benefit from the learning and experience of mature PV technologies as it strives to define, and overcome, the hurdles to PSC commercial impact.