A facile, low-cost and industrially feasible method to implement complex structured perovskites, in stable, C-based perovskite solar cells

Abstract

A series of complex structured perovskites, with multiple cations and mixed I/Br halides, have been prepared and integrated in mesoscopic carbon based perovskite solar cells (PSCs). A comparative study has been performed among 4 different formulations and the beneficial role of Cs and Rb in this type of devices has been highlighted. Even though the preparation of perovskite precursors and the corresponding PSCs have been performed entirely under ambient and uncontrolled conditions, by taking advantage of the recently reported deposition engineering techniques, a complete crystallization at the photoactive perovskite phase has been succeeded, as demonstrated by the high photocurrent density values that have been obtained, which exceed 22 mA/cm2. All of the devices have attained satisfactory efficiency values, which have a great potential for further improvement, by optimization of the individual charge transfer layers. It has been demonstrated that in the triple mesoscopic C based PSC configuration (TiO2/ZrO2/C), inserting formamidinium (FA) cations in the perovskite precursor results in an overall efficiency which is improved by >17%, while a further increase is noted with additional Cs and Rb incorporation in the perovskite formulation. It is of high importance that the method that has been used is antisolvent free, while the PSCs are additionally hole transport material (HTM) free and highly stable overtime, with no need for encapsulation, retaining their initial PCE for more than 30 days of shelf life, while the stability study is still on-going. The fabrication technique applied has proven to be universal, providing working devices for each one of the perovskite compositions under study and at the same time is simple, low-cost and compatible with up-scaling, with no further modifications. By using Electrochemical Impedance Spectroscopy it has been profound that the addition of Cs and Rb in the perovskite precursor lowers the series resistance of the corresponding PSCs, thus contributing to the highest PCE values obtained. At the same time the increase of the recombination resistance, with a simultaneous unaffected charge transfer resistance overtime have been elucidated and justify the stable output of the devices. The study that is being presented provides significant information about the exploitation of mixed cation perovskites, in realistic conditions, for achieving stable and low cost carbon based solar conversion devices.