Iodine-based perovskite solar cells are relatively cheaper and more efficient than conventional solar cells but their stability might pose a problem.
AsianScientist (Jan. 4, 2017) – Researchers have found that gaseous iodine produced by widely used perovskite materials make them inherently unstable and therefore unsuitable for use as solar cells. Their findings have been published in Nature Energy. Perovskites are a type of crystalline material that can be formed using a wide variety of different chemical combinations. Of the many different perovskites formulations that can be used in solar cells, methylammonium lead iodide perovskite (MAPbI3) has been the most widely studied. Solar cells made of this material have been able to reach efficiencies exceeding 20 percent and are cheaper to manufacture than silicon. Unfortunately, the short lifespan of MAPbI3 has prevented it from becoming a viable silicon solar cell alternative. To create better solar cells, members of the Energy Materials and Surface Sciences Unit at the Okinawa Institute of Science and Technology Graduate University (OIST) have been investigating the cause of rapid degradation of these perovskite solar cells. Their results suggest that the degradation of MAPbI3 perovskites may not be a fixable issue. The team led by Dr. Wang Shenghao found that iodide-based perovskites will universally produce a gaseous form of iodine during operation, which in turn causes further degradation of perovskite. While many researchers have pointed to other possible causes of degradation, such as moisture, atmospheric oxygen and heat, the fact that perovskite solar cells continue to degrade even in the absence of these factors led Wang to believe that an intrinsic property was causing the breakdown of material. “We found that these perovskite solar cells are self-exposed to iodine vapor at the onset of degradation, which led to accelerated decomposition of the MAPbI3 perovskite material into PbI2,” Wang explained. “Because of the relatively high vapor pressure of gaseous iodine, it can quickly permeate the rest of the perovskite material, causing damage to the whole solar cell.” This research does not rule out the probability of using perovskites in solar cells, however. “Our experimental results strongly suggest that it is necessary to develop new materials with a reduced concentration of iodine or a reinforced structure that can suppress iodine-induced degradation, in addition to desirable photovoltaic properties,” said Professor Qi Yabing, leader of the Energy Materials and Surface Sciences Unit and corresponding author of the present study. Accordingly, the OIST researchers are continuing to investigate different types of perovskite materials to find more efficient, cost-effective, and long lasting perovskite materials. Their ultimate goal is to make solar cells that are affordable, efficient and stable so that they will be more accessible to the general population.