The emergence of perovskite solar cells
(PSCs) recently has brought new hope to the solar cell industry due to their incredible
improvement of the power conversion efficiency (PCE), which can now exceed
20.0% within seven years of tremendous research. The efficiency and stability
of PSCs depend strongly on the morphology and type of materials selected as the
electron transport layer (ETL) in the device. In this review, the functions of
the ETL based on titania (TiO2) in n–i–p architecture PSCs, including planar
heterojunction and mesoporous-structured devices, are reviewed in terms of the
device performance and stability. Studies found that the application of
suitable fabrication techniques and manipulation of the nanostructural
properties of TiO2 are crucial factors in ameliorating the short-circuit
current density, JSC, and fill factor, FF, of PSCs. On top of that, the effect
of substituting TiO2 with other potential inorganic materials like zinc oxide
(ZnO), tin oxide (SnO2), ternary metal oxides, and metal sulphides, as well as
organic semiconductors including fullerene, graphene, and ionic liquids,
towards the photovoltaic properties and stability of the devices are also
elaborated and discussed. Meanwhile, the utilization of non-electron transport
layers (non-ETLs), such as alumina (Al2O3) and zirconia (ZrO2), as the
mesoporous scaffold in PSCs is found to enhance the open-circuit voltage, VOC,
of the devices.