Solar cells using lead-free hybrid perovskites – SuperSansPlomb

Objective 1: combined theoretical/experimental approach. First principles simulations with DFT to estimate the structure, band gaps and dielectric constants of lead-free perovskite materials. Fabrication of films and colloidal nanocrystals of lead-free materials (alloys and others) by chemical methods. Characterisation by XRD and neutron scattering.

Objective 2. HTM materials based on triangulene and triphenylamine will be prepared by means of classical organic synthesis.

Objective 3. Charge transfer processes will be studied by the techniques of steady-state and time-resolved spectroscopy. The devices will be investigated by the techniques of transient photovoltage and photocurrent and by electrochemical impedance spectroscopy.
Objective 4. The study of solar cells ageing (by I-V curves and IPCE) will be carried out in the specific ageing chamber as a function of several parametres: humidity, temperature, and irradiation. The EPR techniques will be used to identify the degradation mechanisms.

Objective 5. The photovoltaic devices of various morphology will be fabricated and tested. In parallel, their behaviour will be simulated using SILVACO codes as well as structural and optical modelisations, DFT and FDTD.

We have developed novel molecular materials including fused triphenylamine moieties : three original materials have been obtained in less than 5 steps and characterized. A series of nanocrystals of CsPb1-xMx(IyBr1-y)3 (x = 0.25-1, y = 0-1, M : metals) with a decreased lead concentration has been synthesized and tested. Films of lead-free compounds of MA3Bi2Br9 of good quality have been prepared and tested in cells showing promising results.
Structural studies of classical perovskites have been performed on ESRF synchrotron showing their preferential orientation as a function of the presence of chlorine and the nature of the substrate. Neutron scattering studies on ILL facility allowed elucidating the role of cations (MA, FA, Cs, Rb) in the stabilisation of the perovskites structure.
A drift diffusion model has been developed for the perovskite solar cells using implementation within a SILVACO software adopting the known model for the III-V semiconductors and modeling the I(V) and C(V) characteristics and integrating available physical parameters. A reasonable agreement with the literature has been obtained and this initial work has been recently published.
Complete literature review and exhaustive screening of the pure possible lead-free compounds obtained by metallic substitution has allowed to formulate the propositions of the materials that the SyMMES partner fabricated experimentally.
A reference cell perovskite cell achieved a maximum performance of 15%. Interface hole-blocking layer of WO3 printable at low temperature has allowed fabrication of the state-of-the–art cells’ performances. These devices have been electrically characterized at XLIM and by FOTON (C(V)) to initiate the modeling at the device scale.

- Fabricate lead-free double perovskite films using Ag-Bi combination and others.
- Fabricate lead-free solar perovskite solar cells
- Simulate by DFT the lead-free and lead-deficient perovskite alloys
- Select and characterize optimal ETL materials for the best cells
- Carry our the modelling f the complete device based on lead-free materials

1. A. Gheno,* T. T. T. Pham, C. Di Bin, J. Bouclé, B. Ratier, and S. Vedraine,* “Printable WO3 Electron Transporting Layer for Perovskite Solar Cells: Influence on Device Performance and Stability”, Solar Energy Materials & Solar Cells 161 (2017) 347-354
2. Bouchard, M.; Hilhorst, J.; Pouget, S.; Alam, F.; Méndez, M.; Djurado, D.; Aldakov, D.; Schulli, T. U.; Reiss, P. “Direct Evidence of Chlorine Induced Preferential Crystalline Orientation in Methylammonium Lead Iodide Perovskites Grown on TiO2” J. Phys. Chem. C 2017, 121 (14), 7596.
3. Yong Huang, S. Aharon, Alain Rolland, Laurent Pedesseau, Olivier Durand, et al.. « Influence of Schottky contact on the C-V and J-V characteristics of HTM-free perovskite solar cells” EPJ Photovoltaics, EDP sciences, 2017, 8, pp.85501. <hal-01495026>

Metalorganic lead halide perovskites have emerged recently as a very promising class of materials for photovoltaics. Perovskite solar cells combine high efficiency (>20%) with ultra-low cost fabrication via low temperature solution processes and have a high potential for use e.g. in building integrated photovoltaics. Yet, the main drawbacks to be overcome for making out of the scientific breakthrough a real technology are (a) the presence of lead, (b) the limited understanding of detrimental processes (e.g. device hysteresis) and (c) the limited stability. SuperSansPlomb addresses the following key issues: i) Coherent design of lead-free perovskites using combined theoretical and experimental screening; ii) Device integration and study of the fundamental processes governing the charge generation and transfer in the lead-free perovskite solar cells; iii) Development of selective contacts and blocking layers yielding optimized solar cell performance and long term stability.