Energetic I-III-VI2 and I-2-II-IV-VI4 nanocrystals: synthesis, photovoltaic and thermoelectric applications

Due to the promising applications in low-cost and high performance photovoltaic and thermoelectric devices, there has been a booming development of syntheses of colloidal I-III-VI2 and I-2-II-IV-VI4 (I = Cu, Ag; II = Zn, Cd; III = Al, Ga, In; IV = Ge, Sn; VI = S, Se, Te) nanocrystals during the past ten years. In this review, we aim to summarize comprehensively recent developments of I-III-VI2, I-2-II-IV-VI4 nanocrystals, where we focus more on synthetic procedures towards controlled phases and bandgaps. Combining with already achieved theoretical understanding, we try to find some common features of different synthetic routes, which might be extended to synthesize other I-III-VI2 and I-2-II-IV-VI4 nanocrystals with intentioned phases and bandgaps. We also highlight some of the latest advances in applications of these nanocrystals in photovoltaic and thermoelectric devices. Finally, we point out some problems and challenges existing in the fields based on our understanding, e.g., bandgap evaluation, precise cation occupation determination and relatively high cost generated during the synthetic procedures of nanocrystals.