Organic/Inorganic Hybrid Solar Cells Based On CdSe Quantum Dots

Cadmium selenide (CdSe) nanocrystal has been widely used in photovoltaic, bio-labeling and light emitting diode and so on due to its mature synthesis, high electron mobility and tunable band gap. CdSe quantum dots (QDs) can not only been used in quantum dot sensitized solar cells but can also be blended with conjugated polymer to fabricate organic/inorganic hybrid solar cells (HSCs), which have gained exciting results. This dissertation was based on the synthesis of CdSe QDs and focused on the effect of modification of CdSe QDs on the performance of HSCs. Meanwhile, we also explored the usage of CdSe in perovskite solar cells as electron transporting material because of its high electron mobility.In chapter 1, we introduced the basic principles of solar cells, the architecture of HSCs, donor and accepter materials and progresses of HSCs. At the end of this chapter, the fabrication methods, structures and electron transport/extraction materials of perovskite solar cells were reviewed.In chapter 2, we synthesized CdSe QDs with good dimensional homogeneity and dispersity via hot-injection method. The surface of CdSe QDs were modified using n-butanethiol (nBT) and ethane-1,2-dithiol (EDT) before or after the active layers were spin-coated. We also studied the influence of different modification methods on the surface chemical states of CdSe QDs and performance of HSCs based on poly(3-hexylthiophene) (P3HT)/CdSe QDs. Pre-ligand exchange and post deposition ligand treatments could both replace the long as-synthesized alkyl ligands of CdSe QDs. Compared to the pre-ligand exchange, the post-ligand treatments with nBT and EDT showed better power conversion efficiency (PCE) due to its undestroyed interconnective morphology and the improved electron mobility, which were beneficial for charge transfer and collection, leading to a better performance.In chapter 3, we tried to introduce the low band gap conjugated polymer, poly[[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b’]dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl]] (PTB7) as electron donor, with CdSe QDs to fabricate HSCs based on i-n structure. An optimized PCE of 2.61% was obtained through tuning the donor/acceptor ratio and the active layer morphology.The synthesized CdSe QDs own high electron mobility and film forming ability. In chapter 4, we firstly introduced CdSe QDs into perovskite solar cells as electron transport/extraction material. Perovskite films with good coverage and crystallinity were fabricated via a simple "one-step" method. Through tuning the annealing temperature and thickness of CdSe films, perovskite solar cells with a highest PCE of 11.7% were achieved.