Enhancing Power Factor in n-type Chalcopyrite CdSnAs₂ Thermoelectrics via Supercooled Solidification

The practical application of thermoelectric (TE) materials is often limited by the relatively underdeveloped performance of n-type materials compared to their p-type counterparts. Chalcopyrite CdSnAs2 is a promising n-type semiconductor for thermoelectric applications owing to its narrow bandgap around 0.3 eV and exceptionally high electron mobility of 103–104 cm2 V–1 s–1. In this study, we investigated the crystal growth, microstructure, and thermoelectric properties of CdSnAs2. Contrary to conventional understanding of unidirectional melt growth, CdSnAs2 samples grown at higher cooling rates exhibited better crystallinity, whereas some cracks were observed in those cooled more slowly. Thermal analyses revealed that a phase transition from sphalerite to chalcopyrite occurred after solidification in slowly cooled samples, resulting in the formation of dislocations and cracks due to lattice mismatch between the phases. In contrast, rapid cooling induced supercooling, which lowered the solidification temperature and enabled the phase transition to occur in the presence of a residual liquid phase, thereby leading to a more favorable microstructure. As a result, the sample grown at the highest cooling rate (7.6 K min–1) achieved an ultrahigh power factor of 3180 μW m–1 K–2 at 600 K and a peak ZT of 0.59 at 682 K. The power factor of CdSnAs2 surpasses that of conventional binary n-type TE materials such as SnSe and PbTe, underscoring its strong potential for intermediate-temperature thermoelectric applications.