We report optical measurements on MAPbI₃solar cells, together withab initiosimulations, to investigate the material property changes across the tetragonal to cubic phase transition.

Compact TiO₂ is replaced by a low-temperature solution-processed TiO_X/60-PCBM layer for electron extraction in perovskite solar cells with high steady conversion efficiencies.

Tungsten oxide $\left({\text{WO}}_3\right)$ was inserted as an anode interfacial layer between the photoactive layer and top electrode in inverted polymer solar cells (PSCs) with nanocrystalline titanium dioxide as an electron selective layer. The device with ${\text{WO}}_3$ exhibited a remarkable improvement in power conversion efficiency compared with that without ${\text{WO}}_3$ , which indicated that ${\text{WO}}_3$ efficiently prevented the recombination of charge carriers at the organic/top electrode interface. The dependence of the device performances on ${\text{WO}}_3$ film thickness and different top metal electrodes was investigated. Transparent inverted PSCs with thermally evaporable $\text{Ag}/{\text{WO}}_3$ as a transparent anode were also investigated when introducing a ${\text{WO}}_3$ buffer layer.

Molybdenum trioxide (MoO3) was inserted between the active layer and top electrode in inverted polymer solar cells (PSCs) with nanocrystalline titanium dioxide as an electron selective layer. The performances of structurally identical PSCs with different top electrodes (Au, Ag, and Al) were investigated and compared. The interface between MoO3 and different metals was studied by x-ray photoelectron spectroscopy. The results showed that the performances of devices with different metals are greatly improved due to the incorporation of MoO3 and the open-circuit voltage of devices is relatively insensitive to the choice of the anode metal when MoO3 is introduced.

Large single crystals serve as an ideal platform for investigating intrinsic material properties and optoelectronic applications. Here we develop a method, namely, room-temperature liquid diffused separation induced crystallization that uses silicone oil to separate the solvent from the perovskite precursors, to grow high-quality perovskite single crystals. The growth kinetics of perovskite single crystals using this method is elucidated, and their structural and optoelectronic properties are carefully characterized. The resultant perovskite single crystals, taking CH₃NH₃PbBr₃ as an example, exhibit approximately 1 µs lifetime, a low trap density of 4.4 × 10⁹ cm⁻³, and high yield of 92%, which are appealing for visible light or X-ray detection. We hope our findings will be of great significance for the continued advancement of high-quality perovskite single crystals, through a better understanding of growth mechanisms and their deployment in various optoelectronics. The diffused separation induced crystallization strategy presents a major step forward for advancing the field on perovskite single crystals.