Perovskite’s Progress

The Problem: we need power that is renewable and carbon-neutral.

Potential Solutions: nuclear, wind, hydro and solar.

Potential Problems With the Potential Solutions:

Nuclear—waste segregation  for 100,000 years, expensive plants that only last 50 years at best

Wind—not always available, but good start

Hydro—not nearly enough rivers and too many snail darters

Solar—expensive, and we need a lot of them

Solution: make solar so cheap as to be ubiquitous by economics alone. Traditional silicon cells have to be made in expensive, high-temperature processes, like growing a single crystal and slicing it, sputtering other materials on it, etc. Enter alternative materials, such as perovskite (CaTiO₃. Actually ^XIIA^2+VIB⁴⁺X²⁻₃, but I digress). Perovskites can be manufactured with low-cost, low-energy wet methods (except maybe some annealing of deposited TiO₃ ). In one-step solution processing, a lead halide and a methylammonium halide can be dissolved in a solvent and spin coated onto a substrate. Such spin-coated cells recently have shown efficiencies above 20%, competitive with silicon cells. You can make perovskite cells at home without spincoating:

The weird thing about the preceding video is that it was one of many.  A LOT of people are looking into perovskites for solar power applications…which is good, because there are a few problems.

Perovskites are prone to degrade under air and water. Bummer, seeing as how solar cells sit on rooftops with lots of both handy.  Researchers have begun to tackle this problem, most recently from the Graphene Flagship at Instituto Italiano di Tecnologia (IIT) and the University of Rome Tor Vergata, who have significantly enhanced the stability of perovskite solar cells by adding a MoS₂ buffer layer to retain 93% of the initial light conversion efficiency after 550 hours, compared to only 66% for cells without the MoS₂ buffer layer. This is impressive as heck, especially since the MoS₂ layer is sprayed on, keeping costs and power requirements low. Evidently the MoS₂ layer prevents ion migration from the electrode, and aids in hole mobility.

 

Homework:

Solar Cells: Few-Layer MoS2 Flakes as Active Buffer Layer for Stable Perovskite Solar Cells (Adv. Energy Mater. 16/2016)