In Situ Synthesis of PbS Nanocrystals in Polymer Thin Films from Lead(II) Xanthate and Dithiocarbamate Complexes: Evidence for Size and Morphology Control

Edward A Lewis,Paul D Mcnaughter,Paul O’Brien,Sarah J Haigh,Johannes A M Awudza,Selina A Saah,Zhongjie Yin,James Raftery,Jack R Brent,Yiqiang Chen,M Azad Malik

doi:10.1021/cm504765z

Abstract

Lead sulfide has been grown from single molecular precursors within a polymer matrix to form networks of PbS nanocrystals. These materials are model systems for the processing of polymer–nanoparticle layers for flexible hybrid photovoltaic devices. Processing is achieved by spin coating a solution containing the precursor and polymer onto a substrate, followed by heating of the film to decompose the precursor. The effect of precursor chemistry has been explored using lead(II) dithiocarbamates, their 1,10-phen adducts, and lead(II) xanthates with different alkyl chain lengths (butyl, hexyl, and octyl). The xanthates were found to be more promising precursors giving control over nanocrystal size and shape on variation of the alkyl chain length. The lead(II) octyl xanthate complex causes anisotropic growth, forming PbS nanowires within the polymer matrix.

Highlights

We focus on exploring new chemistry which could be applicable to PbS containing hybrid photovoltaics
In this work we investigate a range of precursor chemistries to identify single source precursors for the fabrication of hybrid PbS−polymer thin films
The precursor should not decompose at ambient temperature or upon exposure to air or moisture

Summary

INTRODUCTION

Polymer thin films containing inorganic semiconducting nanostructures have been investigated for a wide range of applications including solar cells,[1−5] light emitting diodes,[6−9] photodiodes,[10] and chemical sensors.[11,12] Hybrid photovoltaics combine conjugated polymers with nanoscale inorganic semiconductors and can potentially exploit the properties of both the organic and inorganic components.[13−15] These systems offer potential for band gap engineering,[5] solution processing, and compatibility with roll-to-roll production methods.[13]. This synthetic route involves no additional ligands and allows improved contact at polymer−inorganic interfaces and between adjacent nanocrystals, leading to improved charge separation and transport.[31,32] In situ methods are synthetically simpler and have potential for large scale processing, e.g., roll-to-roll manufacturing.[16,17,30]. Optimal photovoltaic cell film morphologies should possess fine phase separation, so excitons are never generated far from an interface, and unhindered pathways should exist for efficient transport of charge carriers to the electrodes.[13,14] To achieve this, highly interconnected nanodimensional networks of nanocrystal and polymer are required.[1,32,46] To fully exploit the potential advantages of the in situ approach it is essential to develop methods for morphological control that are equivalent or superior to those demonstrated for ex situ nanocrystal synthesis. The majority of the existing in situ literature has focused on complexes of ethyl xanthates,[4,5,31,32,48] a selection of alternate xanthates have been investigated for their potential improved solubility and device performance.[29,33] We explore a broad range of novel precursor chemistry, taking inspiration from the extensive range of xanthate and dithiocarbamate complexes developed for the

EXPERIMENTAL SECTION

RESULTS AND DISCUSSION

CONCLUSIONS

■ ACKNOWLEDGMENTS

■ REFERENCES