In the initial phases of NANOPTO, we focused on the synthesis of different nanocrystals in order to assess which material was more promising to achieve the final aim of the project of fabricating efficient solar cells and LEDs, and test the proposed dot-in-matrix concept. In early 2017, we developed a novel synthesis of perovskite nanocrystals that can be carried out at room temperature. Importantly, our synthetic method demonstrated nearly 100% photoluminescence efficiency following a post-synthesis chemical treatment. This exciting result induced us to focus on this material for developing solar cells and LEDs operating in the visible range. Meanwhile, we started investigating the dot-in-matrix concept in lead sulphide nanocrystals in combination with the functionalization of the nanocrystal surface.
In 2017, we fabricated a solar cell based on our perovskite nanocrystals. Before proceeding with the device fabrication, the pristine perovskite nanocrystals were treated to substitute the bromine atoms in their structure with iodine. This procedure reduces the energy bang gap of the material, thus allowing the full visible spectrum to be absorbed. The fabricated solar cells demonstrated an efficiency above 5%. In parallel with this activity, we studied the surface treatment of lead sulphide nanocrystals and we demonstrated that substituting the native organic molecule found on their surface with a mixture of zinc iodide and an organic acid leads to improved charge transport. Following these results, we focused on the fabrication of LEDs employing the two materials. In particular, we use the perovskite nanocrystals to fabricate a solution processed LED operating in the visible range (green emitting) with an efficiency above 6%. We achieved this result by tuning the synthesis of the perovskite nanocrystals and optimizing the device fabrication procedure. Finally yet importantly, we developed LEDs employing the surface modified lead sulphide nanocrystals. In particular, we observed a strong enhancement of the photoluminescence efficiency when the lead-sulphide nanocrystals are dispersed in a matrix of nanocrystals with the same composition but of smaller size in combination with zinc oxide nanoparticles. In fact, the two latter components acts as a passivating matrix to the emitting large lead sulphide nanocrystals enhancing both the photoluminescence efficiency and the charge transport.
Importantly, we have presented our results in various international conferences both in Europe and in the USA and our findings have been shown to the publics as well, at a workshop organized at ICFO and by participating in the “pint of science” international event in Barcelona. We have now publish a total of 5 peer-reviewed articles concerning our findings during the development of NANOPTO.
