Perovskite solar cells are in development as candidates for next-generation photovoltaic modules, but commercial use remains limited by long-term instability caused in part by migrating ions in the absorber layer. A team from Helmholtz-Zentrum Berlin (HZB) and the University of Potsdam has now measured the ion density in four commonly used perovskite compounds and found substantial differences between lead- and tin-based materials.
Over the past decade, perovskite research has mainly focused on organometallic compounds in which lead occupies the B-position in the ABX3 crystal structure. Lead-perovskite solar cells have achieved energy conversion efficiency that has increased from about 4 percent to over 27 percent, but the use of toxic lead and limited device lifespan remain major drawbacks.
The lead cation can be replaced with tin, a non-toxic element, to remove lead from the device. Tin-based perovskite solar cells currently show lower efficiency than leading devices, but this could reflect the early stage of research into tin systems rather than a fundamental limit. Dr. Artem Musiienko, who heads an HZB research group, notes that “in purely theoretical terms, tin-based perovskite solar cells could even surpass the efficiency of lead-based perovskites.”
The study focuses on one of the main causes of instability in perovskite cells, the presence of mobile halide ions that move through the lattice, accelerating material degradation and reducing efficiency during operation. Musiienko’s team, together with the Antonio Abate group from HZB and the Felix Lang group from the University of Potsdam, examined four representative perovskite compositions and determined both the density of mobile ions and their migration behavior.
“We found not only that tin-based perovskites have a lower concentration of mobile ions, but also that they intrinsically exhibit a degradation time five times slower than that of lead-based perovskites,” says Musiienko. The tin-perovskite materials were fabricated in the HZB Hysprint laboratory using two solvent systems: one compound synthesized with dimethyl sulfoxide (DMSO) and another produced with an alternative DMF DMI solvent. The solvent variation approach demonstrates a way to avoid tin oxidation, coupled with strong DMSO coordination, consistent with previous studies reported in Chemistry of Materials in 2022.
The measurements show that the lead-based perovskite had the highest mobile ion density of the samples examined. The ion density was slightly lower in the mixed lead tin perovskite and in a tin perovskite made with the conventional solvent. An important result came from the tin perovskite processed with the alternative solvent: “This was really unexpected: these FASnI3 solar cells have ten times fewer mobile ions than the Pb-based solar cells. We also found that they showed excellent stability during operation for more than 600 hours,” reports PhD student Shengnan Zuo from Musiienko’s team.
The work strengthens the case for expanded research into tin-based perovskites as candidates for stable, lead-free thin-film solar cells. ‘We are convinced that tin-based perovskites have enormous potential and that exploring these materials is a very good idea. There are opportunities to significantly increase their efficiency and stability. This study paves the way for the development of innovative, stable thin-film solar cells with suppressed ion migration,” says Musiienko.
