Perovskite Solar Cells and Materials

- Perovskite Materials

Perovskite materials are widely considered to be the successor to silicon because they are lightweight and far cheaper to produce. However, the promise of perovskite has yet to be realized because of the difficulty of replicating lab results in mass production. 

In the field of photovoltaic technologies, silicon-based solar cells make up 90 percent of the market. In terms of cost, stability and efficiency (20-22 percent for a typical solar cell on the market), they are well ahead of the competition. However, after decades of research and investment, silicon-based solar cells are now close to their maximum theoretical efficiency. As a result, new concepts are required to achieve a long-term reduction in solar electricity prices and allow photovoltaic technology to become a more widely adopted way of generating power. 

One solution is to place two different types of solar cells on top of each other to maximize the conversion of light rays into electrical power. These "double-junction" cells are being widely researched in the scientific community, but are expensive to make. Perovskite's unique properties have prompted a great deal of research into its use in solar cells over the last few years. Perovskite allows high conversion efficiency to be achieved at a potentially limited production cost.

[Perovskite Solar Cell - Dennis Schroeder / National Renewable Energy Laboratory

- Perovskite Solar Cell

A perovskite solar cell is a type of solar cell which includes a perovskite structured compound, most commonly a hybrid organic-inorganic lead or tin halide-based material, as the light-harvesting active layer. Perovskite materials such as methylammonium lead halides are cheap to produce and simple to manufacture.

Solar cell efficiencies of devices using these materials have increased from 3.8% in 2009 to 22.7% in late 2017 in single-junction architectures, and, in silicon-based tandem cells, up to 26.7% and 25.2% in 4-terminal and 2-terminal configuration respectively. Perovskite solar cells are therefore the fastest-advancing solar technology to date. With the potential of achieving even higher efficiencies and the very low production costs, perovskite solar cells have become commercially attractive, with start-up companies already promising modules on the market by 2017.

- Main Challenges of Perovskite Devices

A major challenge in the field is that perovskite devices are more prone to degradation than silicon when exposed to moisture, oxygen, light, heat and voltage. The problem is to find which perovskites combine high-efficiency performance with adaptability to environmental conditions.

Perovskites have the general structure of ABX3, where A is an organic (carbon-based) or inorganic group, B is lead or tin, and X is a halide (based on chlorine, iodine, or fluorine, or combinations thereof). As a result, "the number of possible chemical combinations is simply enormous.  Furthermore, they require separate and combined evaluations against multiple environmental conditions, which renders the hyperparameter space impossible to explore using traditional trial-and-error methods.

The chemical parameter space is huge. Testing all of them would be time consuming and tedious.

- Finding Reliable and Low-cost Solar Cells Using Machine Learning

Hybrid perovskites are organic-inorganic molecules that have received a lot of attention in the past 10 years for their potential use in renewable energy. Some are as efficient as silicon in making solar cells, but they are cheaper to make and lighter in weight, potentially enabling a wide range of applications, including light-emitting devices. However, they tend to degrade more easily than silicon when exposed to moisture, oxygen, light, heat and voltage.

The researchers used machine learning-based algorithms and high-throughput experiments to find reliable, low-cost and identify the highest-quality perovskites from a very large field of possible structures. Research have found that it is possible to forecast the materials' dynamic behavior with very high accuracy, without the need to perform as many experiments.

[More to come ...]