Charge extraction from colloidal inorganic nanocrystals

PhD ceremony: Ms. K. Szendrei, 14.45 uur, Doopsgezinde kerk, Oude Boteringestraat 33, Groningen

Dissertation: Charge extraction from colloidal inorganic nanocrystals

Promotor(s): prof. M.A. Loi

Faculty: Mathematics and Natural Sciences

This thesis describes several alternative routes to facilitate charge extraction from PbS nanocrystals (NCs) and their application in hybrid photodetectors and inorganic solar cells. Chapter 2 focuses on the fabrication and study of hybrid thin film PDs composed of [6,6]-phenyl-C61-butyric acid methyl ester and PbS NCs. Efficient photoinduced electron transfer from the NCs to the fullerenes is evidenced by timeresolved photoluminescence (PL) spectroscopy. The PDs show a responsivity of up to 0.32 AW-1 and a detectivity of 2.5*1010 Jones at 1200 nm, which is comparable to that of commercial PDs. In chapter 3 we investigate the successful binding of a fullerene derivative, namely 3,4-dihexyloxyphenyl-C61-butyric-acid to PbS and CdSe NCs in solution. The surface modification phenomenon was evidenced by steady-state and timeresolved PL experiments. The electrically active nature of the thin films of the new complexes is proven by current-voltage measurements. In chapter 4, we report on the fabrication of efficient PbS solar cells, showing a power conversion efficiency approaching 4%. The fabrication method is based on layer-by-layer post deposition ligand exchange using benzenedithiol (BDT) molecules, which increases the electronic coupling between NCs. The effect of 2 different NC sizes on the performance and key parameters of the devices are discussed together with peculiar features of the device functioning. Finally, chapter 5 demonstrates how the characteristic parameters of PbS solar cells change with decreasing temperature. Additionally, extensive optical studies before and after BDT treatment indicate the presence of nonradiative pathways at lower temperatures originating from defect states formed after surface modification.