A simple strategy for synthesizing highly luminescent carbon nanodots and application as effective down-shifting layers

We propose a novel strategy to prepare highly luminescent carbon nanodots (C-dots) by employing a hydrothermal method with citric acid as the carbon source and ethylenediamine as the nitrogen source, together with adding moderate ammonia water (AW) to achieve both appropriate inner structure and excellent N passivation. The effect of pH value and AW amount on the luminescence properties has been thoroughly investigated. The photoluminescence quantum yield of the resultant C-dots reaches as high as 84.8%, which is of 10.56% higher than that of the C-dots synthesized in the absence of AW in the reaction precursors. We have further combined the highest luminescent C-dots with polyvinyl alcohol to form luminescent down-shifting layers on silicon nanowire solar cells. An effective enhancement of short-circuit current density has been realized and the contribution of the down-shifting has been extracted quantitatively from the deterioration of surface reflectance and the gain of the optical absorption redistribution by means of a theoretical model on external quantum efficiency analysis.