Morphological and photophysical aspects of hybrid polymer-nanoparticle systems

International Conference on Hybrid and Organic Photovoltaics
Proceedings of International Conference on Hybrid and Organic Photovoltaics 2015 (HOPV15)

Poster, João Paulo de C. Alves, 389
Publication date: 5th February 2015

Organic solar cells are interesting devices for solar energy conversion due to the possibility of low-cost production, mechanical flexibility, solution processability and high transparency. However, organic solar cells have lower charge carrier mobility and narrower spectral range absorption of solar energy compared to inorganic-based photovoltaic devices. Thus, hybrid solar cells based on polymer-nanoparticle mixtures have attracted attention because of the combination of high optical absorbance of conducting polymers and tunable optical band gap of inorganic nanoparticles. PbS nanoparticles are promising candidates for efficient devices because of their high electron mobility and broad absorption spectra. Usually, PbS nanoparticles are stabilized with organic ligands to assist their dispersion in suitable solvents and avoid aggregation. Oleic acid is the most used organic ligand during PbS nanoparticles synthesis. Post-fabrication treatments have been proposed for ligand exchange and improvement of performance of polymer-PbS devices. Thus, efficiency values greater than 4% have been achieved for this type of device [1]. In this work, the morphological and photophysical properties of polymer-PbS systems were investigated, before and after post-fabrication treatments with ethanedithiol (EDT) and cetyl trimethylammonium bromide (CTAB). The polymers studied were P3HT, PCPDTBT, F8BT e PSBTBT. The PbS nanoparticles employed were synthesized with a diameter of 5 nm.  The addition of PbS to the polymer solutions promoted an increase in light absorption and a quenching of polymer emission. The films were investigated using atomic force microscopy (AFM) and Kelvin probe force microscopy (KPFM). Polymer films show homogeneous aspect and low surface roughness. With the incorporation of PbS nanoparticles, hybrid films became less homogeneous, more aggregated and there was an increase in the size of domains. EDT and CTAB post-fabrication treatments intensify these effects, as demonstrated by AFM images. Ligand-exchange can decrease the interparticle distance, promoting the reorganization of the films. A comparison between these treatments revealed that atomic passivation with Br^- (CTAB) showed a more expressive effect than EDT treatment.

[1] Yuan, J.; Gallagher, A.; Liu, Z.; Sun, Y.; Ma, W. High-efficiency polymer–PbS hybrid solar cells via molecular engineering. J. Mater. Chem. A, 2015, 3, 2572.

© FUNDACIO DE LA COMUNITAT VALENCIANA SCITO