All-Inorganic Germanium Nanocrystal Films by Cationic Ligand Exchange

Abstract

We introduce a new paradigm for group IV nanocrystal surface chemistry based on room temperature surface activation that enables ionic ligand exchange. Germanium nanocrystals synthesized in a gas-phase plasma reactor are functionalized with labile, cationic alkylammonium ligands rather than with traditional covalently bound groups. We employ Fourier transform infrared and (1)H nuclear magnetic resonance spectroscopies to demonstrate the alkylammonium ligands are freely exchanged on the germanium nanocrystal surface with a variety of cationic ligands, including short inorganic ligands such as ammonium and alkali metal cations. This ionic ligand exchange chemistry is used to demonstrate enhanced transport in germanium nanocrystal films following ligand exchange as well as the first photovoltaic device based on an all-inorganic germanium nanocrystal absorber layer cast from solution. This new ligand chemistry should accelerate progress in utilizing germanium and other group IV nanocrystals for optoelectronic applications.

Solution Processing of Hydrogen-Terminated Silicon Nanocrystal for Flexible Electronic Device

“…Similar strong improvement of the conductivity by controlling surface ligands has been reported for colloidal semiconductor NC films. [10][11][12] Among many kinds of colloidal semiconductor NCs, colloidal silicon (Si) NCs have several advantages such as the high environmental-friendliness and the high compatibility with the current semiconductor technology. [13][14][15] A variety of electronic devices has been developed by using Si NC films: thin-film transistor (TFT) [16][17][18] , light-emitting diode [19][20][21][22][23][24][25] , solar cell [26][27][28] , and photodetector 29,30 .…”

Ligands as a universal molecular toolkit in synthesis and assembly of semiconductor nanocrystals

“…Nuclear magnetic resonance (NMR) spectroscopy has been used to quantify the average areal density of surface ligands, 60 progression of ligand exchange reaction, 61 or adsorption/ desorption dynamics of ligands. 62 In many cases, original or incoming ligands have a distinguishable marker in a hydrocarbon chain (e.g., methine proton) that locates at downeld (ca.…”

Growth kinetics of colloidal Ge nanocrystals for light harvesters

“…Till now, there have been some attempts of colloidal Ge-NC for photovoltaic or transistor devices by spinning solutions of colloidal Ge NC to grow a porous Ge-NC lm. 14,41,42 This approach is typically limited by a poor conductivity of the absorbing media and also suffers from the loss of quantum effects in NCs assembly lm. In order to improve the charge carrier transport performance, we mixed Ge NCs in PEDOT:PSS polymer to form a hybrid conductive lm.…”