The Investigation Of Electron Collection Layer In Organic Solar Cells

Photovoltaic (PV) technology, which generates electricity directly from sunlight, isa promising solution to the energy crisis. Intensive research is searching for highefficiency solar cells with low-cost fabrication. Organic semiconductors show greatpromise owing to their low temperature processing, the possibility of producinglightweight, flexible, easily manufactured, and inexpensive solar cells。 Buildingefficient organic solar cells (OSCs) therefore requires a systematic consideration andunderstanding of three key issues: materials design, morphology, and interfaceengineering. In this thesis, firstly we introduced the prospects of the development ofsolar cells, then gave the basic principles of OSCs as well as research progress, andlastly we will focus on the cathode buffer layer investigation for efficient hole andelectron collection in organic photovoltaic solar cell based on the poly(3-hexylthiophene)(6，6)-phenyl-C60-butyricacidmethyl ester (P3HT: PCBM) system, which certainlyimprove the overall performance．The relevant works reported are shown as followed：1. We present a comprehensive study of an efficient inverted OSC based onP3HT:PCBM as active layer integrated with an n-type doped small molecular electroncollection layer (ECL), which is formed by a Cs2CO3-doped tris(8-hydroxyquinolinato)aluminum (Cs2CO3: Alq3) film. The inverted OSC exhibits a maximum powerconversion efficiency of4.83%by optimizing the doping concentration and filmthickness of the Cs2CO3:Alq3ECL. As determined by photoelectron spectroscopy andelectrical measurements, the Cs2CO3doping induces suitable energy level alignment atthe ITO/Cs2CO3: Alq3/PCBM interface and the increase in bulk conductivity of organicECL, which are favorable to electron extraction through Cs2CO3: Alq3to ITO cathode.In addition, optical simulation indicates that the Cs2CO3: Alq3layer can act as an optical spacer to modulate the region of highest incident light intensity within the photoactivelayer, where absorption and charge dissociation are efficient.2. We report on a new concept of the full-organic carrier collection layer (CCL)based organic solar cells with P3HT: PCBM as the active layer. The CCL is composedof solution processed4,7-Diphenyl-1,10-phenanthroline (Bphen) as ECL anddipyrazino[2,3-f:2’,3’-h] quinoxaline-2,3,6,7,10,11-hexacarbonitrile (HAT-CN) as holecollection layer (HCL). The chlorine-free solvents (formic acid (FA) and methanol(MeOH)) processed ECLs exhibit the superiority in good solubility, smooth surfacemorphology and environmental protection in contrast to the ECL based on thecommonly used chlorobenzene (CB). The OSCs based on the chlorine-free ECLsexhibit good photoelectric properties, especially, the FA based device shows an efficientPCE of4.3%in contrast to that of CB based devices. Moreover, a strong electronacceptor molecule of HAT-CN is further introduced into device as a HCL, exhibiting adifferent mechanism in hole extraction by functioning as a charge recombination zonefor electrons injected from Al anode and holes extracted from the donor materials. Theexcellent capabilities of carrier extraction, low temperature procedure andenvironmental stability of CCL provide a facile approach to open anenvironment-friendly energy source.3. We use a novel class of pyridine derivatives including p-PPTNT and m-MPyCNas ECL to fabricate organic solar cells with P3HT: PCBM as the active layer. The devicebased on p-PPTNT and m-MPyCN by optimizing the process and thickness can obtainan enhanced PCE of3.88%and3.919%, respectively.