|SCIENTIFIC DISCIPLINARY SECTOR||CHIM/04|
|MODULES||This unit is a module of:|
"PV cell architecture, materials, morphology and stategy to achieve an efficient Organic Photo Voltaics-OPV. Characterization of active semiconductors, processability, blending properties, absorption spectrum, electrodes with different work functions as well as methods of preparation of thin films for a multilayered OPV. "
Aim of this laboratory is to introduce students to basic experimental procedures employed for the realization of an organic photovoltaic (OPV) cell. The course will include the study of materials, of the device architecture, and of their properties. Another aim of the curse is to introduce students to characterization of the electrical and optical properties of photovoltaic cells, either organic or inorganic in order to assess their performance and the fundamental physical-chemical mechanism which are hindering their efficiency.
Lectured delivered during the lab with Power Point presentations, examples, use of working devices, practical activity, data recording and data analysis
Module A will mainly be devoted to engineering and fabrication of OPV devices
A) DEVICE ENGINEERING
• Device Engineering and material selection
After a brief remainder of the structure and property of a bulk heterojunction OPV cells, the student will define two suitable device architectures (e.g. planar junction, bulk heterojunction, use of hole and/or electron blocking layers etc) and select the proper active materials. The student will compare properties of materials available on the market for optimizing the following main building blocks of a OPV cell:
1) Device electrodes (typically ITO coated glass for the anode and silver paste for the cathode)
2) Holes and electron injection layers (e.g. PEDOT-PSS as hole transport material)
3) Photoactive materials (e.g. regioregular polyalkylthiophenes (rrPATs) as electron donor and [6,6]-Phenyl C61 butyric acid methyl ester (PCBM) as electron acceptor)
According to the selection made in module A, the following fabrication steps will be performed:
• Thin film deposition from solution for material characterization
Students will investigate deposition techniques (e.g. spin-coating, drop casting) and evaluate the most appropriate one through spectroscopy. Casting of suitable materials (e.g. PEDOT-PSS, rrPAT, PCBM, and rrPAT:PCBM blends). In this phase it will be possible for them to investigate the effect of different loads of PCBM, and post-deposition treatments (i.e. thermal annealing and solvent annealing) to probe the role of polymer conformation on the film properties.
• Device realization (deposition of thin active layers and electrodes) and material characterization
After optimization, the active layers will be casted on anode coated glass, and cathodes will be prepared by modified silver paste or other commercially available metallic inks. Optical properties of materials (both as solutions and thin films) such as transmittance and/or reflectance spectra will be recorded for thin films during fabrication. Photoluminescence spectroscopy will be used to control the degree of charge-transfer achieved in rrPAT:PCBM blends.
C) Electro-optical device characterization (this part will be performed di module B – details can be found there)
D) ANALYSIS (in common with module A)
• Critical data analysis
The electrical data for the different cells will be compared with the different parameter used for their growth in order to understand their role on cell performances. Particular focus will be devoted to the comparison of electrical properties with the optical ones recorded in module C. Critical comparison of the performance of the best organic cell produced with a commercial silicon one will be also performed.
• Feedback to the growth and characterization steps
The assessment of the performances on the devices will be used to provide suggestion to improve materials, architectures and fabrication performed in module A and B.
M.C. Petty "Molecular Electronics", Wiley 2007.
Materials Concepts for Solar Cells” by Thomas Dittrich (Imperial College Press)
J. Nelson “The physics of solar cells”, Imperial college Press, 2003
DAVIDE COMORETTO (President)
FRANCESCO BUATIER DE MONGEOT (President Substitute)
MARIA CATERINA GIORDANO (Substitute)
Check official schedule on the course website as well as communication by the Master Course coordinator/teachers.
All class schedules are posted on the EasyAcademy portal.
Oral exam held by two professors, one of them being D. Comoretto, F. Buatier de Mongeot, Maria Caterina Giordano.
The duration of the exam is no shorter than 30 minutes.
The exam consists in the discussion of data recorded and analyzed during the lab activity.
The student must demonstrate comprehension of the main features related to the physical/chemical/technological fundamentals of the device, characterization and materials as well as device realization by using the suitable technical vocabulary (up to 15/30).
The clarity of presentation (up to 5/30) and ability to answer questions (up 10/30) will be also evaluated.
Goal of the exam is to verify the achievement of the class aims.
If aims are not achieved, the student is invited to make a deeper study and to ask the teacher for additional explanations before repeating the exam.
In order to guarantee the correspondence between aims and exam topics, the detailed program is uploaded to AulaWeb and described at the beginning of the course.
A general background of Organic and inorganic photovoltaic cells will be provided in the “Polymers for Electronic and Energy Harvesting” class (SERP+ students) and “Solar cell: functional principles and materials” class (Scienza e Ingegneria dei Materiali students).