Halide Perovskites



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Doctoral position available (secured funding) - Time resolved Kelvin Probe Force Microscopy investigations of third generation solar cells and optoelectronic interfaces

par abergonzoni -

Location : Interdisciplinary Research Institute of Grenoble, SyMMES laboratory,
STEP group, CEA-Grenoble 17 avenue des Martyrs, 38054 Grenoble, France.

Duration : 3 years, CEA fixed term contract Remuneration : 2060 Eur/month
(gross salary)

Contact : Dr. Benjamin Grévin benjamin.grevin cea.fr +33 4 38 78 46 15

Project description

Tremendous progress have been achieved over the last 10 years in the fields of thirdgeneration solar cells based on hybrid perovskites and organic materials. Thanks to their outstanding optoelectronic properties, hybrid perovskites have enabled <code>achieving power conversion efficiencies over 20%. On their side organic cells have experienced a real revival thanks to the use of new non-fullerene electron acceptor (NFA) molecules, with record efficiencies over 18% in 2020. Whatever the technology, the active layers display a heterogeneous morphology and/or structural and chemical defects at the nanometer scale. To further improve device performances, it is essential to better understand the impact of the anostructure and defects on the photo-carrier dynamics ; it is crucial to identify the sources of photo-carrier losses by trapping and recombination. Mastering the photo-carrier dynamics is also the key to improve the performances of smart 2D/0D photodetectors based on novel optoelectronic interfaces that combine the outstanding properties of two dimensional transition metal dichalcogenides and
metal halide perovskite nanocrystals.
In the STEP laboratory, we pursue cutting-edge research in the field of near-field microscopy techniques applied to the study of photovoltaic materials and optoelectronic devices. We have accumulated years of experience in coupling the Kelvin Probe Force Microscope (an electrostatic variant of the Atomic Force Microscope) with illumination sources, for nanoscale investigations of the surface photo-voltage (electrostatic potential generated by the charges created under
illumination). Very recently, we have implemented a pump-probe version of the Kelvin Probe Force Microscope, which allows recording "near-field movies" at the nanoscale of the surface photovoltage dynamics with sub-microsecond time resolution. This thesis aims at using a set of state of the art time-resolved KPFM modes (covering dynamics from the s to 100ns scales) combined with non-contact atomic force microscopy (AFM) under ultra-high vacuum, to study the photo-carrier dynamics in relation with the nanostructure in the active layers of third generation solar cells and in 2D/0D photodetectors. In hybrid perovskites, the challenge will be to gain a better understanding of the relationship between ion migration processes, and the photo-carrier trapping and recombination mechanisms. In 2D/0D optoelectronic interfaces, we will use ppKPFM to investigate the trap-release dynamics processes that ultimately condition the timeresponse of the operating devices.

Context & resources available for the PhD project

To carry out his/her research, the PhD will benefit from STEP facilities for near field microscopy. The nc-AFM/KPFM studies will be performed out on an ultra-high vacuum AFM setup (ScientaOmicron), which controller has been interfaced with several modulated laser sources for pumpprobe measurements, and equipped for state of the art KPFM (heterodyne KPFM with a multidemodulator digital lock in, MFLI-ZI). Complementary characterizations will be carried out on the institute self-service AFM (Brüker ICON). Our research will be funded over the next 4 years by two running contracts from the French National Agency of Research (projects Trapper and Matra2D), this ensures that all the expenses related to the PhD activities will be fully covered (experimental consumables, setup repairs, participation to conferences).
The PhD will be carried out under the supervision of Benjamin Grévin (CNRS, Research Director). He has more than 20 years of experience in scanning probe microscopy techniques, and he has an international standing in the field of non-contact AFM and Kelvin Probe Force Microscopy applied to photoactive materials and devices. He has developed in Grenoble several innovative near fieldbased approaches, such as Qplus-AFM driven nanostenciling and pump-probe KPFM in data cube mode.

STEP group (Synthesis, Structure and Properties of Functional Materials) is an interdisciplinary team within SyMMES comprising chemists, physico-chemists, and physicists, whose joint research coversfundamental and device-oriented approaches of molecular and hybrid functional materials, developed for opto-electronic applications, energy conversion and storage, and sensors.

SyMMES (Molecular Systems and nanoMaterials for Energy and Health) is a laboratory created by the French Alternatives Energies and Atomic Energy Commission (CEA), the National Centre for Scientific Research (CNRS), and Grenoble Alpes University (UGA). SyMMES aims to develop basic research on themes with strong societal issue : zero-carbon energy, information and communications technology (ICT), biotechnology and human health.

Candidate profile / applications

The applicant should have an excellent academic record in Physics, Engineering, Material Sciences or related areas (Master 2 degree, Engineering School Diploma, or equivalent Diploma). She/he should be highly motivated to conduct experimental research in an interdisciplinary team. Strong interest in scanning probe microscopies, nanosciences, and photovoltaics are expected. Candidates must have a good knowledge of English for the promotion of the work (writing articles) as well as good communication skills(communications in conferences). Applications including a cover letter, a curriculum vitae, academic records, should be sent to benjamin.grevin cea.fr. Recommendations (with contact details) will also be appreciated