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PROJECT BASED LABORATORY ON ORGANIC PHOTOVOLTAIC (OPV) CELL

CODE 104101
ACADEMIC YEAR 2021/2022
CREDITS 1 credit during the 2nd year of 9017 Materials Science and Engineering (LM-53) GENOVA
SCIENTIFIC DISCIPLINARY SECTOR FIS/03
LANGUAGE English
TEACHING LOCATION GENOVA (Materials Science and Engineering)
SEMESTER 1° Semester
MODULES This unit is a module of:
TEACHING MATERIALS AULAWEB

OVERVIEW

This laboratory would like to bridge the gap between fundamental and practical knowledge providing the way to build and characterize simple photovoltaic cell both commercially available and prepared by students. PV cell architecture, materials, and strategy to achieve an efficient Organic Photo Voltaics-OPV are critically discussed. 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 will be characterized.

AIMS AND CONTENT

LEARNING OUTCOMES

In this project-based laboratory course students will be guided through the basic experimental procedures for the fabrication and characterization of an organic photovoltaic (OPV) cells as well as the comparison with inorganic solar cells. Each step of the OPV cell fabrication will be done by the students independently and actively, but under continuous guidance and supervision of a tutor. Students will be then guided through the most appropriate experimental techniques and procedures. Once the devices are fabricated and characterized, the student will be engaged in a critical analysis of the results exploiting basic concepts learnt in other courses. To achieve this goal, students will avail themselves of a laboratory entirely dedicated to this activity, aiming to a “learn by making” instruction level.

AIMS AND LEARNING OUTCOMES

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.

 

PREREQUISITES

Basic skills in solution preparation and chemistry of materials. Basic know-how on the electronic structure of semiconductors. Basic know-how of optical and electrical properties of materials.

TEACHING METHODS

Lectures delivered during the lab with Power Point presentations, examples, use of working devices, practical activity, data recording and data analysis.

 

SYLLABUS/CONTENT

Student will make an electrical characterization of inorganic solar cells in order to understand the role of their optical response, electrodes, the meaning of I-V curve as well as of internal and external quantum efficiency.

Unit 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)

 

Unit B) FABRICATION

According to the selection made in unit 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.

 

Unit C) Electro-optical device characterization

  • Optical characterization (total reflectance) of inorganic and organic devices will be performed to evaluate the light intensity coupled to the device.
  • Current-voltage (I-V) curves will be measured on both inorganic and organic devices under controlled illumination conditions to determine the photo-conversion characteristics (Isc, Voc and fill factor) and the efficiency. The impact of series and shunt resistance on the I-V curves will be also critically discussed. Similar data will be also recorded for a commercial silicon solar cell.
  • Measurement of the spectrally resolved External Quantum Efficiency (EQE) , combination with the Reflectance spectrum of the device and estimate of the Internal Quantum Efficiency (IQE). These measurements will allow to evaluate the main effects determining the loss of photo-conversion efficiency.

 

Unit D) ANALYSIS

•             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 unit 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 I and II.

 

RECOMMENDED READING/BIBLIOGRAPHY

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

 

Check official schedule on the course website as well as communication by the Master Course coordinator/teachers.

TEACHERS AND EXAM BOARD

Exam Board

DAVIDE COMORETTO (President)

PAOLA LOVA

FRANCESCO BUATIER DE MONGEOT (President Substitute)

MARIA CATERINA GIORDANO (Substitute)

LESSONS

TEACHING METHODS

Lectures delivered during the lab with Power Point presentations, examples, use of working devices, practical activity, data recording and data analysis.

 

LESSONS START

Check official schedule on the course website as well as communication by the Master Course coordinator/teachers.

Class schedule

All class schedules are posted on the EasyAcademy portal.

EXAMS

EXAM DESCRIPTION

Oral exam held by two professors, one of them being D. Comoretto, F. Buatier de Mongeot, M. C. 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.

ASSESSMENT METHODS

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.

FURTHER INFORMATION

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).