High Efficiency Lead-Free Perovskite Solar cells for indoor-outdoor Applications

In 2009 Kojima et al.,1 reported the first hybrid organometal halide perovskites as visible-light sensitizers for pho- tovoltaic cells. They studied the photovoltaic function of the organic-inorganic lead halide perovskite compounds methylammonium (CH3NH3+, MA) PbBr3 and MAPbI3 as visible-light sensitizers in photoelectrochemical cells, open- ing a fruitful worldwide field of research. Halide perovskites, generally are represented as AMX3, where A is an alkyl ammonium cation, such as MA, dimethyl-ammonium ((CH3)2NH+, DMA), formamidinium (CH3(NH2)2 +, FA), or Cs; M is Pb2+, and X is a halide ion (I-, Br-, Cl-).Although the efficiency of hybrid perovskite solar cells is today competitive with Si, achieving power conversion efficiencies exceeding 23%,2 some drawbacks regarding these systems are the environmental toxicity of water-soluble Pb, and their air/humidity stability. In order to solve these disadvantages a fervent research is currently going on, and in 2016, materials with complete replacement of lead in the perovskite structure, by other cations such as nontoxic Ag+ and Bi3+ , leading to the double perovskite Cs2AgBiBr3(Cl6) structure,3,4 were synthesized. Amazingly, very soon, in 2019, these new perovskites exhibited increasing power conversion efficiencies up to 2.5%.5-7This work aims to present the HELFO (High Efficiency Lead-Free Perovskite Solar cells for indoor-outdoor Appli- cations) project and the preliminary results on fully-inorganic lead-free Cs2AgBiBr6(Cl6) double-cations perovskites. HELFO is a challenging interdisciplinary project, which involves three Institutions of CNR from both fundamental con- densed matter (CNR-ISM-Roma) and applied physics (CNR-IMM-Lecce) fields up to plant biology (CNR-ISPA-Lecce) field, aiming to combine different competences intrinsically belonging to CNR. Semitransparent lead-free Cs2AgBiBr6 and Cs2AgBiCl6 perovskites are synthesized by using both in-situ ultra-high vacuum molecular beam epitaxy deposition and ex-situ solution-processing, and investigated by XRD, SEM/AES/PL and UV-Visible optical techniques. Further- more, these materials will be applied in green-houses for investigating, indoor-and-outdoor, the influence of solar light radiation shielding, through the Cs2AgBiBr6(Cl6) perovskites, on seed germination and plant metabolic profiles at a molecular level of Artemisia annua and Solanum lycopersicum plant species. Photovoltaic devices will be assembled by matching the Cs2AgBiBr6(Cl6) perovskites-based band alignment, with both electron- and hole-transporting layers.Acknowledgements. This work has been funded through the Research Project @CNR "High Efficiency Lead-Free Perovskite Solar cells for indoor-outdoor Applications (HELFO)".References1 A. Kojima, K. Teshima, Y. Shirai, T. Miyasaka, Organometal halide perovskites as visible-light sensitizers for photo- voltaic cells, Journal of the american chemical society 131 (17) (2009) 6050-6051.2 D. Zhao, C. Wang, Z. Song, Y. Yu, C. Chen, X. Zhao, K. Zhu, Y. Yan, Four-terminal all-perovskite tandem solar cells achieving power conversion efficiencies exceeding 23%, ACS Energy Letters 3 (2) (2018) 305-306.3 E. T. McClure, M. R. Ball, W. Windl, P. M. Woodward, Cs2AgBiX6 (x= Br, Cl): new visible light absorbing, lead-free halide perovskite semiconductors, Chemistry of Materials 28 (5) (2016) 1348-1354.4 A. H. Slavney, T. Hu, A. M. Lindenberg, H. I. Karunadasa, A bismuth-halide double perovskite with long carrier recombination lifetime for photovoltaic applications, Journal of the American chemical society 138 (7) (2016) 2138-2141.5 M. R. Filip, S. Hillman, A. A. Haghighirad, H. J. Snaith, F. Giustino, Band gaps of the lead-free halide double perovskites Cs2BiAgCl6 and Cs2BiAgBr6 from theory and experiment, The journal of physical chemistry letters 7 (13) (2016) 2579-2585.6 F. Igbari, R. Wang, Z.-K. Wang, X.-J. Ma, Q. Wang, K.-L. Wang, Y. Zhang, L.-S. Liao, Y. Yang, Composition stoichiometry of Cs2AgBiBr6 films for highly efficient lead-free perovskite solar cells, Nano letters 19 (3) (2019) 2066-2073.7 E. Greul, M. L. Petrus, A. Binek, P. Docampo, T. Bein, Highly stable, phase pure Cs 2 AgBiBr 6 double perovskite thin films for optoelectronic applications, Journal of Materials Chemistry A 5 (37) (2017) 19972-19981.