Enhancing the efficiency of TiO2–perovskite heterojunction solar cell via evaporating Cs2CO3 on TiO2

In a TiO2-perovskite heterojunction solar cell (TiO2-PHSC), besides the perovskite CH3NH3PbX3, TiO2 as one side of the TiO2/CH3NH3PbX3 heterojunction also plays an important role in the photovoltaic effect. In order to improve the performance of the TiO2-PHSC with the structure of glass/FTO/compact TiO2/mesoporous TiO2/CH3NH3PbI3-xClx /poly-TPD (poly(N,N -bis(4-butylphenyl)-N,N -bis(phenyl)benzidine))/Au, a 2 nanometer thick Cs2CO3 layer is thermally evaporated on the mesoporous TiO2 layer. The short-circuit current density (J(sc)) raises from 17.7 mA cm(-2) to 18.9 mA cm(-2), the open-circuit voltage (V-oc) from 0.81 V to 0.87 V, and the fill factor (FF) from 55.2% to 67.3%; as a result, the power conservation efficiency (PCE) increases from 8.0% to 11.1% under AM 1.5G solar illumination (100 mW cm(-2)). Moreover, in a TiO2-PHSC free of mesoporous TiO2, where Cs2CO3 is evaporated on the compact TiO2 layer, the J(sc), V-oc, FF and PCE values increase from 16.0 mA cm(-2), 0.83 V, 50.8% and 6.7% to 17.9 mA cm(-2), 0.90 V, 59.3%, and 9.5%, respectively. The reasons of the PCE increase for either the first kind of TiO2-PHSC or the mesoporous-TiO2-free TiO2-PHSC with a nanometer-thick Cs2CO3 layer on mesoporous TiO2 or compact TiO2 are discussed. ((c) 2014 WILEY-VCH Verlag GmbH &Co. KGaA, Weinheim)