PbS nanocrystals in hybrid systems for solar cell applications

Many research efforts are focused toward significant improvements of polymeric solar cells efficiency, energy harvesting range, time, and environmental stability. Particular attention is given to hybrid organic/inorganic composites constituted of polymer/lead chalcogenides (PbS and PbSe) nanocrystals (NCs) to extend the spectral sensitivity of cells to near-infrared wavelengths. In this work we report the synthesis and characterization of PbS nanocrystals with absorption edge at 984 nm. The nanocrystals have a cubic crystal structure and size of about 2 nm as found by X-ray diffraction analysis. They were combined with poly(3-hexylthiophene) (P3HT) polymer to obtain P3HT:PbS blends with different PbS loadings. A post-deposition ligand exchange on PbS NCs by 1,2-ethanedithiol (EDT) allowed a better interaction between polymer and nanocrystals as showed by fluorescence measurements. The P3HT:PbS blends were deposited and treated by a layer by layer spin coating process and used as active layer in solar cells having structure glass/ITO/PEDOT:PSS/blend/Al. The major result obtained for this hybrid system is an increase of PCE by about two orders of magnitude with respect to analogous reported cells where a post-deposition ligand exchange was performed.