Lead halide perovskite solar cells with the high efficiencies typically use high-temperature processed TiO2 as the electron transporting layers (ETLs). Here, we demonstrate that low-temperature solution-processed nanocrystalline SnO2 can be an excellent alternative ETL material for efficient perovskite solar cells. Our best-performing planar cell using such a SnO2 ETL has achieved an average efficiency of 16.02%, obtained from efficiencies measured from both reverse and forward voltage scans. The outstanding performance of SnO2 ETLs is attributed to the excellent properties of nanocrystalline SnO2 films, such as good antireflection, suitable band edge positions, and high electron mobility. The simple low-temperature process is compatible with the roll-to-roll manufacturing of low-cost perovskite solar cells on flexible substrates.

SnO 2 has been well investigated in many successful state-of-the-art perovskite solar cells (PSCs) due to its favorable attributes such as high mobility, wide bandgap, and deep conduction band and valence band. Several independent studies show the performances of PSCs with SnO 2 are higher than that with TiO 2 , especially in device stability. In 2015, the first planar PSCs were reported with a power conversion efficiency over 17% using a low temperature sol-derived SnO 2 nanocrystal electron transport layer (ETL). Since then, many other groups have also reported high performance PSCs based on SnO 2 ETLs. SnO 2 planar PSCs show currently the highest performance in planar configuration devices (21.6%) and are close to the record holder of TiO 2 mesoporous PSCs, suggesting their high potential as ETLs in PSCs. The main concerns with the application of SnO 2 as ETL are that it suffers from degradation in high temperature processes and that its much lower conduction band compared to perovskite may result in a voltage loss of PSCs. Here, notable achievements to date are outlined, the unique attributes of SnO 2 as ETLs in PSCs are described, and the challenges facing the successful development of PSCs and approaches to the problems are discussed.

Thin-film photovoltaics based on organic–inorganic hybrid perovskite light absorbers have recently emerged as a promising low-cost solar energy harvesting technology.

Efficient lead halide perovskite solar cells use hole-blocking layers to help collection of photogenerated electrons and to achieve high open-circuit voltages. Here, we report the realization of efficient perovskite solar cells grown directly on fluorine-doped tin oxide-coated substrates without using any hole-blocking layers. With ultraviolet-ozone treatment of the substrates, a planar Au/hole-transporting material/CH 3 NH 3 PbI 3-x Cl x /substrate cell processed by a solution method has achieved a power conversion efficiency of over 14% and an open-circuit voltage of 1.06 V measured under reverse voltage scan. The open-circuit voltage is as high as that of our best reference cell with a TiO 2 hole-blocking layer. Besides ultraviolet-ozone treatment, we find that involving Cl in the synthesis is another key for realizing high open-circuit voltage perovskite solar cells without hole-blocking layers. Our results suggest that TiO 2 may not be the ultimate interfacial material for achieving high-performance perovskite solar cells.

APTES-SAM as an efficient interfacial layer in planar perovskite solar cells, optimizing the interface and enhancing performance.

The carrier concentration of the electron-selective layer (ESL) and hole-selective layer can significantly affect the performance of organic-inorganic lead halide perovskite solar cells (PSCs). Herein, a facile yet effective two-step method, i.e., room-temperature colloidal synthesis and low-temperature removal of additive (thiourea), to control the carrier concentration of SnO quantum dot (QD) ESLs to achieve high-performance PSCs is developed. By optimizing the electron density of SnO QD ESLs, a champion stabilized power output of 20.32% for the planar PSCs using triple cation perovskite absorber and 19.73% for those using CH NH PbI absorber is achieved. The superior uniformity of low-temperature processed SnO QD ESLs also enables the fabrication of ≈19% efficiency PSCs with an aperture area of 1.0 cm and 16.97% efficiency flexible device. The results demonstrate the promise of carrier-concentration-controlled SnO QD ESLs for fabricating stable, efficient, reproducible, large-scale, and flexible planar PSCs.

A perovskite solar cell with a thin TiO2 compact film prepared by thermal oxidation of sputtered Ti film achieved a high efficiency of 15.07%. The thin TiO2 film prepared by thermal oxidation is very dense and inhibits the recombination process at the interface. The optimum thickness of the TiO2 compact film prepared by thermal oxidation is thinner than that prepared by spin-coating method. Also, the TiO2 compact film and the TiO2 porous film can be sintered at the same time. This one-step sintering process leads to a lower dark current density, a lower series resistance, and a higher recombination resistance than those of two-step sintering. Therefore, the perovskite solar cell with the TiO2 compact film prepared by thermal oxidation has a higher short-circuit current density and a higher fill factor.

Mg doping improves interfacial contact and endows low hysteresis high temperature processed SnO2-based PSCs with a steady-state PCE of 14.55%.