Local Probe Microscopies for the Study of Photovoltaic (PV) Materials
Contract type: Fixed term
Starting date: April, 2020
Duration: 36 months
Working Place: Palaiseau
Education: Master 2 ; Engineer
Salary: 28,800 € (annual gross)
IPVF in brief
Become an actor of the Energy Transition by joining a team driven by innovation and impact to address today’s most decisive challenges.
IPVF – Institut Photovoltaïque d’Île-de-France, is a global Research, Innovation and Education center, which mission is to accelerate energy transition through science & technology.
Gathering industrial PV leaders (EDF, Total, Air Liquide, Horiba and Riber) and world-renowned academic research teams (CNRS, Ecole Polytechnique), multi-disciplinary and international IPVF teams conduct research for clean energy technologies.
IPVF at a glance:
- An ambitious Scientific and Technological Program: from tandem solar cell technologies to economy & market assessment, state-of-the art characterization, photocatalysis and concepts breakthrough.
- A state-of-the-art technological platform: more than 100 tools, located in cleanrooms (advanced characterization, materials deposition, prototypes for fabrication, modelling…).
- A high-standard Education program (M.S. and PhD students).
This topic is part of the research and development activities carried out within IPVF and the GeePs (Génie Electrique et Electronique de Paris) laboratory in the field of PV materials and devices. In particular, these studies are conducted at the micro/nano scale using atomic force microscopy (AFM) metrology. In this field we use the C-AFM (Conductive AFM) and KPFM (Kelvin probe microscopy) electrical extensions to study and explore the local properties of different technological building blocks involved in PV devices.
- The student will first have to carry out a bibliography work on C-AFM and KPFM instrumentation, and in particular applied to the study of PV materials and devices. In parallel, he/she will be trained in the use of AFM, with a particular focus on data acquisition and processing. He/she will also participate in the implementation of the KPFM measurement in the time domain where the contact potential difference (CPD) will be measured under pulsed and/or frequency modulated illumination. Several signal processing approaches applied to the surface photovoltage (SPV) measurement will be studied in order to access the characteristic times or phase shifts with the idea to evaluate and map the minority carrier lifetime.
- In a second phase, the student will apply its new expertise to study different technologies developed at IPVF:
- Perovskite materials have grown at an unprecedented rate making possible to produce PV cells with conversion efficiencies of more than 20%. The IPVF is interested in different compositions of these materials, which may show fluctuations in composition due to their polycrystalline structure. These fluctuations can be analyzed by KPFM microscopy.
- Interfaces between perovskite materials and silicon, with a view to the subsequent fabrication of tandem The KPFM analysis can be carried out on different types of interfaces, notably in order to study the band bending between these two materials.
- So-called “Passivating Contacts“ for crystalline silicon (c-Si) absorbers. These structures consist of a very thin layer of silicon oxide (<2 nm) covered by a layer of highly doped polysilicon (10-20 nm). This particular technological block has the advantage of minimizing surface recombination losses by avoiding direct contact between the metal and the c-Si. The electronic transport properties through these passivating layers are nowadays very poorly known and are the subject of advanced characterization work by several research groups around the world. The results of this study should provide additional information on transport mechanisms, and in particular tunnelling transport through ultrathin oxides including the presence of “pinholes”.
- CIGS material used in PV devices is a polycrystalline thin film where the grain boundaries do not always act as recombinant centers, as can be expected in conventional semiconductor devices. The presence of impurities seems to cause a passivation effect. KPFM under illumination can be an interesting approach that can be implemented to study local variations in the open circuit voltage (VOC) and lifetime. Similarly, the C-AFM can be used to analyze the distribution of saturation current in the dark.
The thesis will take place bewteen laboratories of IPVF and GeePs.
- Electrical Engineering.
- Physics of Solar Cells.
- Materials Science.
- Hands-on experience with electrical measurements.
- Knowledge of Origin, Excel
- Communication of results (oral and writing)
- Curious and entreprising.
- Organizational and collaborative skills.