Growth kinetics of colloidal Ge nanocrystals for light harvesters

Abstract

Colloidal Ge nanocrystals (NCs) are gaining increased interest because of their potential application in low-cost optoelectronic and light harvesting devices. However, reliable control of colloidal NC synthesis is often an issue and a deeper understanding of the key-role parameters governing NC growth is highly required. Here we report an extended investigation on the growth of colloidal Ge NCs synthesized from a one-pot solution based approach. A systematic study of the effects of synthesis time, temperature and precursor concentration is elucidated in detail. X-ray diffraction (XRD) analysis reveals the presence of crystalline Ge NCs with a mean size (from 5 to 35 nm) decreasing with the increase of precursor concentration. Such a trend was further confirmed by scanning electron microscopy (SEM) and dynamic light scattering (DLS) analysis. Moreover, the temporal NC size evolution shows a typical saturating behaviour, where characteristic time shortens at higher precursor concentration. All these growth features were satisfactorily simulated by a numerical NC growth model, evidencing that the kinetics of NC growth is controlled by a reaction-limited regime with typical activation energy of 0.7 eV. Finally, light absorption in the visible region and the successful realization of a hybrid photodetector, employing colloidal Ge NCs embedded in PEDOT:PSS polymer, showed the capability of low-cost colloidal Ge to act as light harvester. These results put new understanding for a reliable control of colloidal NC growth and the development of low-cost devices

Enhancing Short-Wave Infrared Photosensitivity of SiGe Nanocrystals-Based Films through Embedding Matrix-Induced Passivation, Stress, and Nanocrystallization

“…Light harvesting was also evidenced in hybrid photodetectors based on colloidal Ge NCs embedded in conductive PEDOT:PSS polymer. 33…”

“…These are possible by tailoring and engineering QDs/NCs/NPs size, − density, composition, , strain, interface with embedding matrix, and shape, by employing core–shell nanostructures , and by doping . These together with the controlled technological processes ensuring reduced Ge oxidation, and NCs/QDs/NPs surface passivation, size control and improved functionality lead to demonstrating the potential of Ge-based NCs/QDs/NPs for optoelectronic and photovoltaic devices, e.g., in photodetectors , and photoMOSFETs for monolithically integrated Si optical interconnects, for light harvesting and solar energy conversion in solar cells ,− or as bioimaging fluorescence probes in biomedical applications. , …”

Investigation of the photophysical properties of energy-relevant inorganic nanocrystals

“…[56][57][58][59][60][61][62][63][64][65] Heating a solution of GeBr2 or GeI2 with a surfactant has also been shown to generate Ge nanocrystals. [66][67][68] Co-reduction of GeI2 and GeI4 is another common strategy for generating Ge nanocrystals in the ~2-20 nm size regime,…”

Germanium–Tin/Cadmium Sulfide Core/Shell Nanocrystals with Enhanced Near-Infrared Photoluminescence

“…[13][14][15][16][17][18][19][20][21][22] Heating a solution of GeBr2 or GeI2 with a surfactant has also been shown to generate Ge nanocrystals. [23][24][25] Co-reduction of GeI2 and GeI4 is another common strategy for generating Ge nanocrystals in the ~2-20 nm size regime, where the precursor ratio controls the particle size. 3,[26][27][28][29][30] The polymerization of [Ge9] 4-or other related Zintl ions, both with and without linking cations such as Ge 4+ or Pt 2+ , generates highly ordered, porous Ge nanocrystals.…”

“…Reduction of germanium halides (GeCl 4 , GeBr 2 , GeI 2 , or GeI 4 ) using strong reducing agents (NaBH 4 , LiAlH 4 , etc.) in the presence of suitable surfactants [oleylamine, octadecene (ODE), and trioctylphosphine (TOP)] is widely used to make monodisperse Ge nanocrystals. − Heating a solution of GeBr 2 or GeI 2 with a surfactant has also been shown to generate Ge nanocrystals. − Co-reduction of GeI 2 and GeI 4 is another common strategy for generating Ge nanocrystals in the ∼2–20 nm size regime, where the precursor ratio controls the particle size. ,− The polymerization of [Ge 9 ] 4– or other related Zintl ions, both with and without linking cations such as Ge 4+ or Pt 2+ , generates highly ordered, porous Ge nanocrystals. − Other preparations involve reduction of Ge-rich oxides, − heat-assisted reduction of the GeH 2 Wittig adduct Ph 3 PCMe 2 ·GeH 2 ·BH 3 , , laser photolysis of Ge­(CH 3 ) 4 or GeH 4 gas, − photolysis of Ge wafer, electroless deposition on preformed Ag nanocrystals, Au-catalyzed vapor–liquid–solid growth using GeH 4 or diphenylgermane, ultrasonic aerosol pyrolysis of tetrapropylgermane, solution or solid phase reduction of NaGe, plasma decomposition of GeCl 4 − or GeH 4 , sulfur-assisted thermal decomposition of triphenylgermanium chloride, and heating a solution of an alkylgermane in various high-temperature organic solvents …”