Perovskite solar cells show tremendous promise in propelling solar power into the marketplace. Typically, the devices use a hole-transportation layer and noble metal based electrodes, which promotes the efficient movement of electrical current after exposure to sunlight. However, manufacturing the hole-transportation materials is very costly, and the devices using such materials lack long-term stability. Besides, the highly energy consumptive process for the deposition of noble metal electrodes hinders its further application.
Publishing in Science, a research group in Wuhan National Laboratory for Optoelectronics of Huazhong University of Science and Technology, led by Professor Hongwei Han, collaborated with Professor Michael Grätzel of EPFL, has developed a fully printable mesoscopic perovskite solar cell that does not use a hole-transporting layer, with 12.84% conversion efficiency and over 1000 hours stability under full sunlight in ambient temperature. The innovation is regarded as a breakthrough in the area of low cost, high efficiency mesoscopic solar cells, which is likely to entail wide spread applications of this new photovoltaic technology.
The scientists employ a double layer of mesoporous TiO2 and ZrO2 as a scaffold infiltrated by a mixed cation lead halide perovskite as a light harvester. No hole conductor or Au reflector is employed as is presently done in all high efficiency perovskite solar cells. Instead, the back contact is simply a printed carbon layer. The perovskite is drop-casted from solution through the porous carbon layer. It has been verified that perovskite formed in the presence of the two organic cations forms crystals with a longer exciton lifetimes and achieves better pore filling of the mesoporous oxide film than the single cation perovskite. As a consequence the PV performance increases dramatically. Using this very simple, extremely cheap and printable heterojunction a strikingly high certified photocurrent density of 22.8 mA cm2 the highest ever reported for a perovskite cell and power conversion efficiency of 12.84% were achieved.‘It is only the beginning of a new era of fully printable PVand certainly new efficiency records will follow this first report,’ Prof. Han said. Indeed, the wide application of lowcost PV technology will benefit for its industrialization in the near future.
Reference
Mei A, Li X, Liu L, Ku Z, Liu K, Rong Y, Xu M, Hu M, Chen J, Yang Y, Grätzel M, Han H. A hole-conductor–free, fully printable mesoscopic perovskite solar cell with high stability. Science 345:6194 DOI: 10.1126/science.1254763
