Webinars Post-Doc du GDR HPERO

• Guest speaker : Polyxeni Tsoulka, CEA Grenoble
• Abstract : Solar cells based on metal-halide perovskite (PK) materials have received much attention the last decade due to their i) high power conversion efficiency (PCE), ii) tunable bandgap energy and iii) low fabrication cost compared to other thin-film and silicon photovoltaic technologies. Moreover, integrating wide-bandgap (WBG) PK materials into tandem solar cell architectures with narrow-bandgap (NBG) absorbers such as silicon, copper indium gallium diselenide and PK, has further boosted the PCE and the PK-based solar cells represent the fastest developing photovoltaic technology to date.
  In this talk, we focus on the PKWBG/PKNBG tandem solar cells, which have now reached the impressive 27.4 % solar cell efficiency1, and we discuss different methods to further improve the PCE. The most commonly used strategies to increase the tandem solar cell performance include : i) the introduction of additives into the PK bulk material to decrease the recombination losses within the bulk, ii) the PK/charge transport interface improvement, i.e. the PK/electron- or hole- transport interface (PK/HTL and PK/ETL respectively) and iii) charge recombination junction engineering. Here, we examine the PKWBG/ETL interface and we seek to decrease the open-circuit voltage (Voc) losses caused by charge recombination phenomena at the interface and poor energetic band alignment.
  Our main studies to improve the PKWBG/ETL interface are performed on single junction solar cells : soda-lime glass/Indium Tin Oxide (ITO)/ [2-(9H-Carbazol-9-yl)ethyl]phosphonic Acid (2-PACz)/(Cs,FA)Pb(I,Br)3/C60/Bathocuproine (BCP)/Ag, where (Cs,FA)Pb(I,Br)3 (FA : formamidinium) is the WBG absorber of 1.73 eV and C60 is the ETL layer. The PKWBG/ETL interface often presents : i) dangling bonds at the PK surface that act as charge recombination centers, ii) charge accumulation and ion migration at the interface that lead to hysteresis phenomena and iii) poor energy band alignment causing inadequate charge extraction or/and charge recombination. Hence, PK surface treatments are among the most widely used strategies to improve the PKWBG/ETL interface quality.
  In this talk, we discuss different PK surface treatments that minimize the charge recombination losses at the interface such as i) the formation of 2D PK layer using FAI or GABr (GA : guanidinium) spin-coating processes or ii) the introduction of thin AlxOy layer using Atomic Layer Deposition. Our findings show that a thin AlxOy layer leads to an impressive increase of the Voc value by around 100 mV. The optimized PKWBG/ETL structure is then integrated into the PK/PK tandem architecture. Our preliminary results show Voc values higher than 1850 mV and good voltage addition of the two PK subcells.

Monday 3rd April 2023 at 09h30 via zoom : "Simulation-based optimization of two terminal perovskite/CIGS tandem solar cells"

• Guest speaker : Aleksandra Bojar (GeePs - IPVF)
• Abstract : Tandem solar cells are one of the most efficient ways to overcome the limits of power conversion efficiency (PCE) of single junction solar cells and today reach PCEs higher than 30% [1]. Perovskite solar cells (PSCs) have been successfully combined with silicon bottom-subcell in tandem configurations, reaching the efficiencies exceeding 32% for two-terminal (2T) configuration [https://doi.org/10.1002/pip.3646]. Despite the promising future of this technology, the use of Si limits the final efficiency of the device due to its indirect band gap of 1.12 eV, which results in significant transmission losses in the infrared and the requirement for thick absorber layer leading to increased material usage and cost [https://doi.org/10.1038/s41598-019-56457-0]. This motivated the research community to search for alternatives, one of them being CuIn(Ga)Se2 (CI(G)S) materials. They offer the advantages of compositional tunable bandgap in the range 1.03 – 1.68 eV combined with a high absorption coefficient, allowing for an all thin-film tandem technology [https://doi.org/10.1016/j.solener.2020.07.007, https://doi.org/10.1002/aenm.201900408, https://doi.org/10.1021/acsenergylett.9b01128 ]. Indeed, perovskite/CI(G)S 2T tandems have been demonstrated with efficiencies as high as 24.2% [https://doi.org/10.1021/acsenergylett.2c00274. Although they still lag behind those of PVK/Si tandems, they have a theoretical potential to reach efficiencies higher than 40% [2]. Reaching this goal will require a dedicated optimization of the device layout with respect to its electrical and optical properties.
  In this work we show the potential of the transfer matrix method (TMM) to simulate and optimize monolithic tandem solar cells based on CI(G)S and perovskite absorbers. Providing that simulation models fits well experimental data, we were able to perform a detailed optical loss analysis. This allowed us to determine sources of parasitic absorption and decreased sub-band gap transmittance, and further to find better substitute materials to improve light absorption and conversion efficiency in the tandem. Our results set guidelines for the 2T perovskite/CI(G)S tandem solar cells development, predicting achievable efficiency of 30%, for the current direction of the perovskite/CI(G)S tandem development.

Monday 6th March 2023 at 09h30 via zoom : "Defect mitigation in halides perovskites : from datamining to photoluminescence"

• Guest speaker : Alexandre PY-RENAUDIE (IPVF)
• Abstract : Self-healing can be defined as the ability for a material to recover its properties after being damaged. This amazing property has been observed experimentally for a famous family of photovoltaic absorbers : the lead halides perovskites. However, the scientific community has not yet reached a consensus on the mechanism behind this phenomenon. We propose in this presentation to look for other materials with properties similar to those of lead halide perovskites, and compare their behavior to better understand the self-healing phenomenon. An initial search with a datamining study will be presented, allowing us to identify properties that we hypothesize are markers of self-healing. Thanks to this finding, we selected a family of suitable compounds, the gold halide perovskites. The synthesis and characterization of those compounds will be presented as well, first in the form of powders and then as thin films. Last but not least, we will present evidence of self-healing in these materials in agreement with the predictions of our model.

Monday 9th January 2023 at 09h30 via zoom : "Controlling the formation process of Methylammonium-Free Halide Perovskite films for a homogeneous incorporation of alkali metal cations beneficial to solar cell performances"

• Guest speaker : Dr. Daming Zheng
• Abstract : Incorporating multiple cations of the IA alkali metal column of the periodic table (K+/Rb+/Cs+) to prepare perovskite films is promising for boosting the photovoltaic properties. However, contrary to K+, both Cs+ and Rb+ suffer from non-uniformity at the origin of performance and stability losses. In our work, Ammonium chloride (NH4Cl) additive is shown to address this concern. We have found the conditions for the preparation of perovskite layers with an homogeneous distribution of multi-alkali metal cations (m-AMC), especially Rb+. The mechanism of ammonium chloride action in m-AMCs perovskites, refined at each preparation process step, has been unveiled. Through a serious analysis, we found that ammonium chloride mainly leads to the formation of intermediates which can increase the solubility of PbI2 and then favor the phase formation and transformation. Secondly, we explored the movement of m-AMCs in the perovskite layer during the film formation process by using the GD-OES (Glow Discharge- Optical Emission S pectroscopy) technique and presented the intuitive evidence of phase segregation caused by potassium. We also confirmed that the atomic ratios change with the depth and that the targeted growth direction of the film is lateral growth. Moreover, we combined this additive with GD-OES detection technology. We found how the additive influence the distribution of m-AMCs film formation. Finally, 22.53% PCE (stabilized at 22.04%) was achieved.
  m-AMCs, it is multi-alkali metal cations. For GD-OES, it is glow discharge optical emission spectroscopy (GD-OES) technique. Thank you.

Monday 5th December2022 at 09h30 via zoom : "Electronic spin coherent evolution in MAPI perovskites"

• Guest speaker : Guadalupe Garcia-Arellano, INSP
• Abstract : Nowadays hybrid metal halide perovskites, such as methylammonium lead iodide CH3NH3PbI3 (MAPI) are the center of many studies due to their outstanding optoelectronic properties as the large and tunable spin−orbit coupling, spin dependent optical selection rules, and predicted electrically tunable Rashba spin splitting [1,2]. Because of the presence of heavy atoms (Pb, I), spin−orbit coupling is very important in lead perovskite materials and makes then possible the optical generation of electronic spins [3]. In this webinar we will discuss the measured transversal spin coherence time in MAPI polycrystalline films by means of a photo-induced Faraday rotation technique (PFR) [4] Thanks to the picosecond resolution of the experimental technique, we can select different excitation energies with a bandwidth of about 1 meV. We have found that is possible to tune, in this way, the coherent electronic spin evolution signal by exciting at different energies. We demonstrate the optical orientation of localized electrons and holes in this perovskite material at low temperature.

[1] Kepenekian, M. et al., Rashba and Dresselhaus effects in hybrid organic inorganic perovskites : from basics to devices, ACS Nano 2015, 9, 11557−11567.
[2] Kepenekian, M. et al., Rashba and Dresselhaus couplings in Halide perovskites : Accomplishments and opportunities for spintronics and spin-orbitronics, J. Phys. Chem. Lett. 2017, 8 (14), 3362− 3370.
[3] Odenthal, P. et al., Spin-polarized exciton quantum beating in hybrid organic−inorganic perovskites. Nat. Phys. 2017, 13, 894−899.
[4] G. Garcia-Arellano, et al., Energy tuning of electronic spin coherent evolution in methylammonium lead iodide perovskites, The Journal of Physical Chemistry Letters 12 (34), 8272-8279

Monday 7th November 2022 at 09h30 via zoom : "Perovskite solar cells developed using electrodeposition"

• Guest speaker : Mirella Al Katrib, LEPMI, France
• Abstract : TIn the last decade, halide perovskites have drawn substantial interest in the fields of photovoltaic. However, the most used method to deposit perovskite active layers is spin coating, which presents many constraints such as limited surface coverage, high production price, non-homogeneity, undefined perovskite crystallinity, poor stability and must be executed under inert atmosphere. Alternative methods must be explored, such as electrodeposition, since it solves the as-mentioned disadvantages. In this work, we were able to develop different types of perovskites using electrodeposition, understand the impact of the different deposition parameters on their structure, and improve their stability comparing to the spin-coated ones. An innovative approach was reached by electrodepositing different mixed perovskites, such as MAPbI3-xClx and MA1-yFAyPbI3-xClx. However, an optimized solar cell architecture must be found, corresponding to the electrodeposited perovskite, to further enhance the efficiency.[1,2]
  
  [1] Al Katrib, M., Perrin, L. & Planes, E. Optimizing Perovskite Solar Cell Architecture in Multistep Routes Including Electrodeposition. ACS Applied Energy Materials (2022) Automatic word wrap
  [2] Al Katrib, M., Planes, E. & Perrin, L. Effect of Chlorine Addition on the Performance and Stability of Electrodeposited Mixed Perovskite Solar Cells. Chemistry of Materials 34, 2218–2230 (2022).

Monday, October 3rd, 9h30 via zoom : "Monolithic perovskite/silicon tandem solar cell : behaviour under light and electrical characterisations"

• Guest speaker : Adrien RIVALLAND, CEA-INES, France
• Abstract : To optimise the conversion of solar energy and increase the electrical power of photovoltaic cells, the development of tandem solar cells seems to be the preferred route. As the photovoltaic industry is heavily focused on the production of silicon-based cells, a structure combining a silicon cell and a large gap material is the most relevant[1].
  Perovskite (PK) / cristalline silicon (c-Si) tandem cells have reached record efficiencies, recently exceeding the symbolic 30% mark (31.25% CSEM/EPFL)[2] at lab scale (1cm²).
  However, even if some studies have demonstrated good stability of perovskite-based cells[3]–[5], this remains very dependent on the precise composition of the perovskite, its deposition process and the nature of the transport layers, which makes it difficult to transpose study conclusions from one laboratory to another.
  The electrical behaviour of tandem cells produced at CEA-INES after ageing under illumination will be presented. The variation of behaviour according to the architecture of the cell and the nature of the different thin layers constituting it will be highlighted. We will also discuss the difficulties that may be encountered in characterising metastable tandem cells compared to stable single junction cells.
  
  [1] ITRPV, “International Technology Roadmap for Photovoltaic,” Itrpv, no. March, 2019, [Online].
  [2] E. Bellini, “CSEM, EPFL achieve 31.25% efficiency for tandem perovskite-silicon solar cell,” pv-magazine, 2022. https://www.pv-magazine.com/2022/07/07/csem-epfl-achieve-31-25-efficiency-for-tandem-perovskite-silicon-solar-cell/ (accessed Jul. 08, 2022).
  [3] M. De Bastiani et al., “Toward Stable Monolithic Perovskite/Silicon Tandem Photovoltaics : A Six-Month Outdoor Performance Study in a Hot and Humid Climate,” ACS Energy Lett., pp. 2944–2951, 2021, doi : 10.1021/acsenergylett.1c01018.
  [4] J. Liu et al., “28.2%-efficient, outdoor-stable perovskite/silicon tandem solar cell,” Joule, pp. 1–18, 2021, doi : 10.1016/j.joule.2021.11.003.
  [5] S. You et al., “Long-term stable and highly efficient perovskite solar cells with a formamidinium chloride (FACl) additive,” J. Mater. Chem. A, vol. 8, no. 34, pp. 17756–17764, 2020, doi : 10.1039/d0ta05676f.

Monday 5th September, 9h30 via zoom : "Hybrid halide perovskites for advanced X-rays detection systems"

• Guest speaker : Ferdinand LEDEE - CEA-Leti, DOPT, Université Grenoble Alpes, France
• Abstract : Advanced X-ray medical imaging systems including phase contrast imaging or artificial intelligence algorithms will require a joint improvement of the detector efficiency and spatial resolution. Today’s commercial flat panel X-ray detectors operate in indirect conversion mode with a trade-off in sensitivity and resolution. Reaching high sensitivity, by increasing the scintillator thickness, goes at the expense of the spatial resolution. Direct detection should combine a high sensitivity and a high spatial resolution but has not been yet implemented in general radiography (20-100 keV energy range) to due to lack of satisfactory semi-conducting material.
  The demanding specifications required are a combination of low temperature processing of thick (>100µm) layers on large area (≈20 x 20 cm²), cost-effective materials and processes, and high-level optoelectronic properties. Specifically, the ideal semi-conductor for X-ray direct detection has to combine good charge transport properties to insure high X-ray-to-electron conversion rate (the so-called sensitivity), while keeping low the leakage current in the dark (the so-called dark current) which limits the flat panel dynamic range and the minimal detectable dose. Developments in perovskite metal halide semiconductors over the last ten years have raised the prospect of achieving all these characteristics.
  In this talk, we will first give some insights about the different perovskites materials and fabrication strategies developed in the literature for the direct detection of X-rays. A more thorough discussion will be carried out on MAPbBr3 single crystals for X-ray detection, and some attempts to reduce the dark current by tuning the halide composition MAPb(BrxCl1-x)3 will be presented. Finally, we will present a solution process in order to grow large area (4 x 4 cm²) thick polycrystalline MAPbBr3 layers directly on a backplane, and a projection toward the final application will be proposed.
  

12 Juin 2022 : "Challenges and advances in scaling-up perovskite solar cells using industrially compatible wet deposition techniques"

• Guest speaker : Iwan Zimmermann - Postdoc researcher at IPVF
• Abstract : Impressive results have been obtained in the field of perovskite solar cells (PSCs) in over a decade of intense research with power conversion efficiencies exceeding 25%. However, poor long-term stability, and obstacles in scale-up currently hold back PSCs from entering the photovoltaic market. This webinar discusses challenges encountered in up-scaling the perovskite technology to the module level and highlights recent progress achieved at IPVF. In a first part, the deposition of tin oxide used as an electron extraction layer is established using chemical bath deposition. Applying this simple low-temperature deposition method, highly homogeneous SnO2 films are obtained in a reproducible manner on large surfaces. In a second part, the deposition of the photoactive perovskite layer is developed using sequential slot-die coating on up to 10 x 10 cm2 substrates. This industrially relevant 2-step deposition technique allows for the growth of high-quality dense perovskite thin films with large grains. Integration of the SnO2 and perovskite layers into mini-modules with aperture areas of up to 40 cm2 is discussed.