Solar cells and other optoelectronic devices require materials that efficiently convert light into electron/hole pairs and electrical currents. A collaborative study led by the Roeffaers and Hofkens lab (KU Leuven) led to the engineering of such a material that can operate for several years. The group of prof. Van Speybroeck at CMM contributed to this research and publication with quantum mechanical insights. The results of our study were recently published in Nature Communications.
Metal halide perovskites are promising materials for optoelectronic applications. They absorb sunlight well, the generated electron/hole pairs can diffuse trough large parts of the materials, and they are inexpensive to produce. Among these perovskites, CsPbI3 continues to receive considerable interest given its superior stability under ambient conditions. The remaining bottleneck is the phase stability of the so-called black phase. This black phase is optoelectronically the most interesting one, but forms spontaneously only at high temperatures. This sought-after phase rapidly degrades at room temperature to a yellow phase with inferior optoelectronic properties. Both the experimental and computational work showed that defining a PbI2 microgrid hinders this degradation and thus drastically increases the material’s long-term stability.
The laser-defined PbI2 microgrid separates the CsPbI3 material into micrometer-sized domains. This created grid acts as an anchoring point for the black phase and prevents the local degradation of one domain from triggering the degradation of neighboring ones. To understand how the microgrid improves the stability of the CsPbI3 black phase, we performed dynamic quantum mechanical simulations. Although computationally expensive, modeling these quantum mechanical interactions is essential to understand what factors influence the relative phase stabilities of the black and yellow phases. We found that the anchoring on the microgrid inhibits the movements necessary for the transformation from the black to the yellow phase, and thus results in a long-term stable black-phase material usable for optoelectronic applications.
CMM authors – Tom Braeckevelt, dr. Sven Rogge, prof. Veronique Van Speybroeck