All-Inorganic Light-Emitting Diodes Based on Solution-Processed Nontoxic and Earth-Abundant Nanocrystals

We fabricate and characterize light-emitting diodes (LEDs) based on thin-films of NiO, Mn-doped ZnS, and
$n$
-ZnO nanoparticles acting as hole-transporting, emitting, and electron-transporting layers, respectively. We vary the thickness of the individual layers and record current–voltage and luminance–current characteristics. By examining the fitting of the current–voltage characteristics of these all-inorganic LEDs, we find that the hole- and electron-transporting layers lower barrier heights for hole- and electron-injection from the respective electrodes that correspondingly improve electro-luminescence (EL) output. The photoluminescence emission of Mn-doped ZnS nanoparticles and EL emission of the LEDs resembled implying that excitons formed in the doped nanostructures followed by a radiative transition between
$d$
-states of Mn-ions.