The Superior Supplies cowl illustration reveals the floor of the halide perovskite construction being modified by a big natural cation. The cation diffuses by the skinny movie to reconstruct the floor construction. Credit score: Superior Supplies
A brand new kind of photo voltaic know-how has appeared promising lately. Halide perovskite photo voltaic cells are each high-performing and low-cost for producing electrical power – two mandatory components for any profitable photo voltaic know-how of the long run. However new photo voltaic cell supplies also needs to match the soundness of silicon-based photo voltaic cells, which boast greater than 25 years of reliability.
In newly revealed analysis, a staff led by Juan-Pablo Correa-Baena, assistant professor within the College of Supplies Sciences and Engineering at Georgia Tech, reveals that halide perovskite photo voltaic cells are much less secure than beforehand thought. Their work reveals the thermal instability that occurs throughout the cells’ interface layers, but additionally affords a path ahead towards reliability and effectivity for halide perovskite photo voltaic know-how. Their analysis, revealed as the duvet story for the journal Superior Supplies in December 2022, has rapid implications for each teachers and trade professionals working with perovskites in photovoltaics, a discipline involved with electrical currents generated by daylight.
Lead halide perovskite photo voltaic cells promise superior conversion of daylight into electrical energy. At the moment, the most typical technique for coaxing excessive conversion effectivity out of those cells is to deal with their surfaces with massive positively charged ions often called cations.
These cations are too massive to suit into the perovskite atomic-scale lattice, and, upon touchdown on the perovskite crystal, change the fabric’s construction on the interface the place they’re deposited. The ensuing atomic-scale defects restrict the efficacy of present extraction from the photo voltaic cell. Regardless of consciousness of those structural adjustments, analysis on whether or not the cations are secure after deposition is proscribed, leaving a niche in understanding of a course of that would impression the long-term viability of halide perovskite photo voltaic cells.
“Our concern was that in lengthy intervals of photo voltaic cell operation the reconstruction of the interfaces would proceed,” mentioned Correa-Baena. “So, we sought to grasp and show how this course of occurs over time.”
To hold out the experiment, the staff created a pattern photo voltaic gadget utilizing typical perovskite movies. The gadget options eight unbiased photo voltaic cells, which allows the researchers to experiment and generate knowledge primarily based on every cell’s efficiency. They investigated how the cells would carry out, each with and with out the cation floor therapy, and studied the cation-modified interfaces of every cell earlier than and after extended thermal stress utilizing synchrotron-based X-ray characterization strategies.
First, the researchers uncovered the pre-treated samples to 100 levels Celsius for 40 minutes, and then measured their changes in chemical composition using X-ray photoelectron spectroscopy. They also used another type of X-ray technology to investigate precisely what type of crystal structures form on the film’s surface. Combining the information from the two tools, the researchers could visualize how the cations diffuse into the lattice and how the interface structure changes when exposed to heat.
Next, to understand how the cation-induced structural changes impact solar cell performance, the researchers employed excitation correlation spectroscopy in collaboration with Carlos Silva, professor of physics and chemistry at Georgia Tech. The technique exposes the solar cell samples to very fast pulses of light and detects the intensity of light emitted from the film after each pulse to understand how energy from light is lost. The measurements allow the researchers to understand what kinds of surface defects are detrimental to performance.
Finally, the team correlated the changes in structure and optoelectronic properties with the differences in the solar cells’ efficiencies. They also studied the changes induced by high temperatures in two of the most used cations and observed the differences in dynamics at their interfaces.
“Our work revealed that there is concerning instability introduced by treatment with certain cations,” said Carlo Perini, a research scientist in Correa-Baena’s lab and the first author of the paper. “But the good news is that, with proper engineering of the interface layer, we will see enhanced stability of this technology in the future.”
The researchers learned that the surfaces of metal halide perovskite films treated with organic cations keep evolving in structure and composition under thermal stress. They saw that the resulting atomic-scale changes at the interface can cause a meaningful loss in power conversion efficiency in solar cells. In addition, they found that the speed of these changes depends on the type of cations used, suggesting that stable interfaces might be within reach with adequate engineering of the molecules.
“We hope this work will compel researchers to test these interfaces at high temperatures and seek solutions to the problem of instability,” Correa-Baena said. “This work should point scientists in the right direction, to an area where they can focus in order to build more efficient and stable solar technologies.”
Reference: “Interface Reconstruction from Ruddlesden–Popper Structures Impacts Stability in Lead Halide Perovskite Solar Cells” by Carlo Andrea Riccardo Perini, Esteban Rojas-Gatjens, Magdalena Ravello, Andrés-Felipe Castro-Mendez, Juanita Hidalgo, Yu An, Sanggyun Kim, Barry Lai, Ruipeng Li, Carlos Silva-Acuña, Juan-Pablo Correa-Baena, 17 October 2022, Advanced Materials.
DOI: 10.1002/adma.202204726
