Near Infrared Photoluminescence from Nonthermal Plasma Synthesized SiGe Quantum Dots Induced by Heterostructuring with Hybrid Perovskite

Colloidal and luminescent quantum dots (QDs) have advantages in the fabrication of optoelectronic devices because they can serve as inks allowing for the printing devices in the form of thin films. Among materials for the production of QDs, silicon (Si) QDs are attractive due to Si’s earth abundance, low toxicity and size-tunable emissions in the visible to near infrared (NIR) spectral range. Alloying germanium (Ge) offers the expansion of emission range of Si QDs through bandgap engineering. The luminescence of Si QDs is limited to < 1000 nm due to the band gap of bulk Si (1.12 eV), which confines their application in the visible range. Ge has a narrower band gap (0.6 eV), and complete miscibility with Si. Therefore, Si and Ge alloy QDs (SiGe QDs) can emit in longer wavelengths compared to pure Si QDs. We demonstrated the synthesis of colloidal SiGe QDs using a nonthermal plasma method. The nonthermal plasma synthesized SiGe QDs were able to form a colloid with benzonitrile without any post-processing for surface functionalization due to their chlorine terminated surfaces. X-ray diffraction and energy-dispersive X-ray spectroscopy verified that the SiGe QDs are spherical and crystalline, and the Ge composition is ~16%. Although NIR PL (> 1000 nm) was expected, the photoluminescence (PL) of SiGe QDs was not detectable. Heterostructuring with hybrid perovskite (CsPbBr₃) was chosen to improve the PL of SiGe QDs; energy or charge transfer from perovskite to SiGe QDs was expected considering the band structure of the materials. Heterostructuring was conducted by spin-coating perovskite and SiGe QD thin films. The sandwich-like structure (perovskite-SiGe QDs-perovskite) was confirmed by cross-sectional transmission electron microscopy. The perovskite PL (at ~520 nm) quenching and the SiGe QD PL (at ~1040 nm) rise were observed in the heterostructure. The PL lifetime of perovskite was also significantly reduced by heterostructuring. Transient absorption spectroscopy (TAS) showed changes in photoinduced absorption in perovskite under the presence of SiGe QDs. The changes in both radiative and nonradiative processes indicate that excited perovskite provided energy or charge to SiGe QDs resulting in PL rise in NIR region.