Development of an inorganic cesium carbonate-based electron transport material for a 17% power conversion efficiency perovskite solar cell device

A low-temperature solution process technique is employed to develop an inorganic cesium carbonate (Cs2CO3) as an electron transport material for inorganic–organic hybrid double cation (FAPbI3)0.85(MAPbBr3)0.15 perovskite solar cells, as an alternative to the conventional thick and meso-TiO2. A device structure of compact-TiO2/Cs2CO3 (0.2 wt. %)/perovskite/spiro-OMETAD leads to enhanced performance of the photovoltaic device, achieving a short-circuit current density (Jsc) of 22.26 mA/cm2, an open-circuit voltage (Voc) of 1054 mV, a fill factor (FF) of 71.6%, and a power conversion efficiency (PCE) of about 17% under one sun illumination, whereas the controlled device structure shows an efficiency of 16.58% without such surface modification layer. Additionally, a device structure of Cs2CO3 (6 wt. %)/perovskite/spiro-OMETAD without any TiO2 ETM has shown a Jsc of 15.40 mA/cm2, Voc of 1023 mV, FF of 51.7%, and a PCE of 8.14%. On the other hand, external quantum efficiency (EQE) data yields around 85% of incident photon to electron conversion for c-TiO2/Cs2CO3 (0.2 wt. %)/perovskite/spiro-OMETAD structure and integrated Jsc extracted from EQE data confirms that Jsc obtained from the current–voltage test is within a close agreement. The obtained results indicate that there is a possibility to further increase the performance of perovskite-based cells and reduce their processing cost by replacing the thick mesoporous TiO2 by Cs2CO3.