Upgraded perovskite design sets solar cells on path to stability

In photo voltaic science, slightly structural concord goes a good distance. By discovering the atomic equal of an ideal handshake between two kinds of perovskite—a category of crystalline supplies prized for his or her means to transform daylight into electrical energy—researchers at Cornell have constructed photo voltaic cells that aren’t solely high-performing, however exceptionally sturdy.

Three-dimensional (3D) perovskites encompass repeating atomic networks of steel halide “cages” which might be linked at their corners and crammed with small, positively charged molecules referred to as cations.

These supplies have proven exceptional promise for enabling photo voltaic cells which might be light-weight, low-cost and able to efficiencies that surpass these of conventional silicon. However regardless of their potential, most 3D perovskites are weak to warmth, moisture and the very daylight they’re designed to seize as a result of their salt-like ionic crystal buildings.

New analysis particulars a first-of-its-kind, two-dimensional (2D) perovskite designed by Cornell researchers that may be layered on prime of a 3D perovskite to behave as a rugged, weather-resistant coating. The outcomes are detailed within the paper “Phase-stabilized 2D/3D hetero-bilayers via lattice-matching for efficient and stable inverted solar cells,” published Might 9 within the journal Joule.

Different researchers have tried this protecting 2D perovskite coating utilizing methylammonium (MA) as a cage cation. Nonetheless, MA is so unstable it begins to vaporize upon publicity to daylight.

“With MA, you have good efficiency and charge transport, but the solar cell degrades rapidly in a few hundred hours of continuous operation,” stated lead writer Shripathi Ramakrishnan, a doctoral candidate within the lab of senior writer Qiuming Yu, professor of chemical and biomolecular engineering at Cornell Engineering.

Makes an attempt have been made to make use of formamidinium (FA)—a extra secure cage cation—within the protective layerhowever an excessive amount of pressure within the materials’s crystal construction imposed by FA’s bigger measurement destabilizes it and prevents the formation of secure 2D lattices.

The brand new breakthrough got here from lattice matching—the concept that if the lattice of 2D perovskite is sized excellent, it’ll “click” along with the 3D perovskite. By deciding on particular natural cations, known as ligands, that naturally align with each the FA cage cation and the encircling crystal construction, the researchers have been in a position to kind 2D perovskites with a layer thickness and configuration that balances conductivity and stability.

“The basic idea is that a ligand in a 2D perovskite tries to shrink the lattice, while the FA cage cation works to make it bigger and you have these two opposing forces at play,” Ramakrishnan stated. “We selected a ligand that doesn’t try to compress the cage too much, allowing it to expand a little and make room for the larger FA cation to fit inside.”

The group efficiently synthesized a brand new 2D perovskite utilizing FA because the cage cation and utilized it as a protecting coating on prime of a 3D perovskite. Characterization strategies—together with synchrotron X-ray diffraction and confocal photoluminescence mapping—revealed that the brand new 2D FA-based layer possesses distinctive stability below mixed mild, temperature and humidity, outperforming its MA-based counterparts.

The 2D-on-3D mixture not solely resists degradation below daylight and warmth; it additionally improves electrical efficiency by enabling smoother movement of costs between the 3D and 2D layers. The ensuing photo voltaic cells achieved a sunlight-to-electricity conversion effectivity of 25.3% and confirmed solely 5% efficiency loss over almost 50 days of intense testing below mixed mild and warmth, making them exceptionally sturdy perovskite photo voltaic cells.

Whereas perovskites have attracted nice curiosity from scientists over the past decade, their instability has held again commercialization of their use in solar cells.

“Silicon had about 50 years to get to where we are with solar. Perovskite hasn’t had 50 years yet, but we can accelerate that progress by understanding it at the molecular level and applying what we learn,” Yu stated.

Ramakrishnan stated an internship, supported by the Nationwide Science Basis’s INTERN program on the Nationwide Renewable Vitality Laboratory in Colorado, gave him a window into the commercialization panorama, the place lab-tested supplies are uncovered to actual out of doors circumstances and in contrast straight with industrial photo voltaic panels.

“This was really inspiring for me—not just the scientific aspect, but also the technological relevance,” Ramakrishnan stated.