Development and studies of thin film nanocrystal based
Development and studies of thin film nanocrystal based photovoltaics. By Mauricio Andrade Ch. E 389 Department of Chemical Engineering Summer 2007
Overview n Objective n Introduction q q n Design of thin film PV q q n Manufacturing design Synthesis Capping Ligands Application of thin film PV Thin Film Challenges q q n Photovoltaic semi conductive materials Capping Ligands Monodispersity Solutions- Absorbing Layer Treatment technique q q Chemical treatment Thermal treatment n Future Work Design n Questions http: //www. pvresources. com/en/technologies. php
Objective To develop a high-efficiency photovoltaic solar cell made of colloidal nanocrystals by providing a commercial route to low-cost manufacturable photovoltaic devices.
Introduction n n A photovoltaic cell is composed of semiconducting materials that release charge carriers upon excitation with light. Electron hole pairs are then separated by an induced potential difference present in the device. http: //www. chemistrydaily. com/chemistry/Bandgap
PV Materials http: //www. pvresources. com/en/technologies. php
Manufacturing Designs Top down n Develop devices from externally controlled assemblies. q q Products are efficient with high degree of purity. Expensive to manufacture Bottom up n Self assembly of smaller components due to their chemical or physical properties. q q Less expensive to manufacture Purity and efficiency is reduced. http: //www. personal. psu. edu/users/j/r/jrs 5004/Solar_Transportation. htm http: //staff. jccc. net/pdecell/chemistry/selfassem. html
Synthesis Objective: n q q q Develop monodisperse photovoltaic nanomaterials Preferably Copper Indium Gallium Diselenide Capable of forming several nanometric size layers
Capping Ligands q By Doh, Lee, unpublished data q Photovoltaic nanocrystals are stabilized by ionic/covalent bonding between the surface of the nanocrystal and hydrocarbon molecules. Self-assembly is caused by the equilibrium between: n Van Der Waals forces n Steric hindrance
Application of Thin Film PV By Dr Bryan Korgel, unpublished data
Thin Film Challenges n Capping Ligands q q Inhibit contact between photovoltaic nanoparticles Poor attachment to the substrate n Monodispersity q n Hard to achieve as the surface area to volume ratio is increased Elimination of elements as components are synthesized (Indium)
Solution. Absorbing layer treatment techniques 1 Chemical treatment n Goal: Remove the capping ligands. n n n Reduction of film volume leads to crack formation. Current method involves exposure to a hydrazine solution. Three different outcomes have been observed:
1. 2. 3. (a), (d) Conductive films where the cracks does not isolate the fragments of the film, making a continuously conductive film. (b), (e) Limited conductive films due to deep cracks on certain regions (c), (f) Nonconductive films that arise from deep cracks in the film and further flecking of conductive materials from the surface.
Solution. Absorbing layer treatment technique Thermal treatment n High temperature exposure of material yield larger grain sizes that increase mobility of charges q q At temperatures below boiling temperature of the capping ligands weight loss is observed. At high temperatures (>500 C) metallic undesired reactions may yield Cu/In alloy or In 2 O 3 depending on the annealing environment.
Future Work Design http: //www. eere. energy. gov/de/solar_electric. html
Questions?
- Slides: 15