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

Abstract

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 (Jsc) raises from 17.7 mA cm–2 to 18.9 mA cm–2, the open-circuit voltage (Voc) 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 Jsc, Voc, 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. (© 2014 WILEY-VCH Verlag GmbH &Co. KGaA, Weinheim)