Since the advent of organic–inorganic hybrid methylammonium (MA) lead halide MAPbX3 perovskites as active materials for photovoltaic applications in 2009, [1] the PCE of perovskite-based solar cells (PSCs) has dramatically increased from the initial 3.8% to a recently certified 22.1%. [2] Emerging from this groundbreaking discovery, an unprecedented scientific research has sprouted in the field of photovoltaics due to their exceptional physical properties. Therefore, the development of cost-effective HTMs with high efficiency along with a good stability is an important task to address.Planar and sulfur-rich polycyclic aromatic hydrocarbons bearing arylamine moieties have demonstrated to be a successful approach for designing new highly efficient HTMs for PSCs. [3] Conventionally, the π-extended conjugation associated with the planar and electron-rich structure of the fused heterocycles enable them to show strong stacking through intermolecular interactions (π‒π, S···S), thereby bestowing enhanced hole-carrier mobilities. This behaviour is beatifully exemplified by anthra[1,2-b:4,3-b′:5,6-b′′:8,7-b′′′]tetrathiophene-based (ATT) HTMs. [4] Here we report a readily available new class of multi-armed, sulfur-rich hole transporting materials based on pi-conjugated central cores. Devices were fabricated using state-of-the-art mixed anion mixed halide perovskite composition with the nominal formula [FAPbI₃]_0.85[MAPbBr₃]_0.15 (FA = formamidinium, MA = methylammonium). The performance of the solar cells employing the novel HTMs were measured under simulated 1 sun irradiation and conversion efficiencies of up to 19 % were obtained.

References

[1]    Kojima A., Teshima K., Shirai Y. and Miyasaka T., “Organometal Halide Perovskites as Visible-Light Sensitizers for Photovoltaic Cells”,J. Am. Chem. Soc., 131, 17, (2009), pp 6050-6051.[2]    National Renewable Energy Laboratory, N.R.E.L.[3]    Molina-Ontoria A., Zimmermann I., Garcia-Benito I., Gratia P, Roldán-Carmona C., Aghazada S., Graetzel M., Nazeeruddin M.K., and Martín, “Benzotrithiophene-Based Hole-Transporting Materials for 18.2 % Perovskite Solar Cells”, Angew. Chem. Int. Ed., 55, 21, (2016), pp 6270-6274.[4]    Zimmermann I, Urieta-Mora J., Gratia P., Aragó J., Grancini G., Molina-Ontoria A., Ortí E., Martín N. and Nazeeruddin M. K., “High-Efficiency Perovskite Solar Cells Using Molecularly Engineered, Thiophene-Rich, Hole-Transporting Materials: Influence of Alkyl Chain Length on Power Conversion Efficiency”, Adv. Energy Mater., (2016), DOI: 10.1002/aenm.201601674.