By: Julian A. Steele, Tom Braeckevelt, Vittal Prakasam, Giedrius Degutis, Haifeng Yuan, Handong Jin, Eduardo Solano, Pascal Puech, Shreya Basak, Maria Isabel Pintor-Monroy, Hans Van Gorp, Guillaume Fleury, Ruo Xi Yang, Zhenni Lin, Haowei Huang, Elke Debroye, Dmitry Chernyshov, Bin Chen, Mingyang Wei, Yi Hou, Robert Gehlhaar, Jan Genoe, Steven De Feyter, Sven M. J. Rogge, …Maarten B. J. Roeffaers
Solar cells and other optoelectronic devices require materials that efficiently convert light into electron/hole pairs and electrical currents. Researchers from various groups, including at KU Leuven (Hofkens and Roeffaers lab) and Ghent University (Van Speybroeck group), have now engineered such a material that can operate for several years.
Metal halide perovskites are materials with properties that make them attractive for optoelectronic applications. They absorb sunlight well, and the generated electron/hole pairs can diffuse through large parts of the material. Moreover, they are inexpensive to produce. Among these perovskites, CsPbI3 continues to receive considerable interest because of its superior stability under ambient conditions. However, this material exhibits these attractive properties only when it adopts its so-called black phase, which forms spontaneously only at high temperatures. At room temperature, this sought-after phase rapidly degrades to a yellow phase with inferior optoelectronic properties. Our work shows that defining a PbI2 microgrid on the material through laser patterning can suppress this degradation. As demonstrated by quantum mechanical simulations, this microgrid hinders the degradation and thus drastically increases the material's long-term stability.
Illustration of anchoring imposed by a microgrid introduced into a thin film.
The quest to stabilize the black CsPbI3 phase is not new. Previous work showed that depositing a thin CsPbI3 film on a substrate could already increase the lifetime of the black phase. In that approach, the film/substrate interface acts as an anchoring point for the black phase, increasing its stability. In the current work, we took this approach a step further by introducing an interface in all three dimensions. We embedded an interfacial microstructure into CsPbI3 through coarse photolithography. The formed PbI2 microgrid separates the material into micrometer-sized domains of the material. This microgrid also acts as an anchoring point and prevents the local degradation of one domain from triggering the degradation of neighboring ones. Both effects result in a yet-unseen improvement in the stability of the black phase. By embedding this microgrid, we could maintain the CsPbI3 films in their wanted black phase for more than 2.5 years, compared to the 10 hours before.
Image of graphic encoded into a microgrid thin film using selective laser destabilization.
To understand how the anchoring improves the stability of the CsPbI3 black phase, at the Center for Molecular Modeling (CMM), we performed dynamic quantum mechanical simulations. Although computationally expensive, modeling these quantum mechanical interactions is essential to understand how to suppress the degradation from the black to the yellow phase. They found that the anchoring on the microgrid inhibits the movements necessary for the transformation from the black to the yellow phase, hindering the phase transformation from occurring. The infrastructure provided by VSC was critical for these simulations, as the model size and simulation duration had to be large enough to capture the effects of the anchoring. This required significant computing power to simulate these large cells with quantum mechanical accuracy.
The quantum mechanical insights obtained with the VSC infrastructure can help to steer future developments for perovskite devices using this novel technique.
Overall, we have shown that a PbI2 microgrid can vastly improve the stability of CsPbI3. The quantum mechanical insights obtained with the VSC infrastructure can help to steer future developments for perovskite devices using this novel technique.
Read the full publication in the Nature Portfolio here.