Low cost, high efficiency, and stability are straightforward research challenges in the development of organic-inorganic perovskite solar cells. Organolead halide is unstable at high temperatures or in some solvents. The direct preparation of a carbon layer on top becomes difficult. In this study, we successfully prepared full solution-processed low-cost TiO2/CH3NH3PbI3 heterojunction (HJ) solar cells based on a low-temperature carbon electrode. Power conversion efficiency of mesoporous (M-)TiO2/CH3NH3PbI3/C HJ solar cells based on a low-temperature-processed carbon electrode achieved 9%. The devices of M-TiO2/CH3NH3PbI3/C HJ solar cells without encapsulation exhibited advantageous stability (over 2000 h) in air in the dark. The ability to process low-cost carbon electrodes at low temperature on top of the CH3NH3PbI3 layer without destroying its structure reduces the cost and simplifies the fabrication process of perovskite HJ solar cells. This ability also provides higher flexibility to choose and optimize the device, as well as investigate the underlying active layers.

Considering the remarkable progress in photovoltaic performance, scholars have focused on perovskite solar cells (PSCs) over the recent two years. TiO 2 thin film is a semiconductor with a wide band gap and is usually used as an electronselective layer (ESL) in PSCs. Although SnO 2 exhibits conductivity higher than that of TiO 2 , its use as a compact ESL in PSCs has not been reported. In this study, nanocrystalline SnO 2 thin film was prepared through a sol−gel method and then characterized. The prepared SnO 2 thin film was composed of small tetragonal rutile nanocrystals. We applied the SnO 2 compact ESL into PSCs and compared their performance with that of PSCs based on a TiO 2 thin layer. SnO 2 -ESL-based PSCs (S-PSCs) showed higher short-circuit current density and lower open-circuit voltage, fill factor, and conversion efficiency than the conventional TiO 2 -ESL-based PSCs. Furthermore, the photovoltaic performance of S-PSCs was highly dependent on measurement means, and this relationship was investigated and is discussed in detail.

The ionic liquid N-butyl-N'-(4-pyridylheptyl)imidazolium bis(trifluoromethane)sulfonimide (BuPyIm-TFSI) was used as a dual-functional additive to improve the electrical properties of the hole-transporting material (HTM) for perovskite solar cells. BuPyIm-TFSI improved the conductivity of HTM and reduced the dark current of the solar cell simultaneously, thereby greatly increasing the power conversion efficiency.