In this work, methylammonium lead trichloride (CH3NH3PbCl3) perovskite thin films were fabricated via a two-step spin coating and solvent-vapor-assisted thermal annealing method under low temperature. The films exhibited cubic crystalline structure and pinhole-free morphologies.The possible charge traps were investigated via the analysis of photoluminescence (PL) spectra of perovskite films prepared with different lead chloride (PbCl2) precursor concentrations while maintaining the same concentration of methylammonium chloride (CH3NH3Cl). Prototypical ultraviolet (UV) photodetectors with the structure of ITO/CH3NH3PbCl3/Poly (triaryl amine) (PTAA)/Al were fabricated and showed low dark current density 1.60 × 10 -5 mA/cm 2 under -1 V reverse bias, strong photoresponse in 300-400 nm region, and a high UV-visible rejection ratio up to 500 under 0 or -0.5 V bias. All the results demonstrated that low-temperature solution-processed CH3NH3PbCl3 perovskite thin films offer a great potential for making flexible, lightweight visible-blind UV-A photodetectors.

Csx(MA0.17FA0.83)1−xPb1−ySny(I0.83Br0.17)3 perovskites with cubic-phase morphologies were deployed in solar cells, achieving high efficiencies and improved stability for high Sn-containing devices.

Poly(3,:poly(styrene sulfonate) (PEDOT:PSS) has been widely used as a hole-conducting polymer in many optoelectronic devices including perovskite solar cells. However, its electrical and surface properties are not well controlled during the conventional ambient annealing. Herein, we apply the solvent posttreatments, including toluene vapor annealing and ethylene glycol (EG) washing, to modify not only the electrical conductivity and work function but also, importantly, the surface composition and morphology of PEDOT:PSS thin films. We show that annealing PEDOT:PSS films in a nonpolar toluene vapor environment results in a slightly enhanced electrical conductivity and increased work function while maintaining the surface composition and morphology. The CH 3 NH 3 PbI 3 perovskite solar cells using the toluene vapor-annealed PEDOT:PSS hole transporting layers (HTLs) yield a 31.8% increase in power conversion efficiency (PCE) from the control devices with the ambient conditionannealed PEDOT:PSS HTLs. All photovoltaic parameters are increased because of reduced trap states at the perovskite/HTL interface, as well as efficient and balanced charge generation, transport, and extraction rates. In contrast, washing PEDOT:PSS films with the polar EG solvent removes the PSS on the surface, increases the surface roughness, and dramatically increases the electrical conductivity by 5 orders of magnitude but slightly decreases the work function. Consequently, the CH 3 NH 3 PbI 3 perovskite solar cells with EG-washed PEDOT:PSS HTLs result in a 28.6% decrease in PCE from the control devices because of the increased trap states at the perovskite/HTL interface, which leads to an inefficient hole extraction. The charge accumulation at the perovskite/HTL interface also reflects in a serious hysteresis of J−V curves in the reversed bias region. This work highlights the importance of controlling both electronic and surface properties of PEDOT:PSS HTLs for the improvement of perovskite solar cell performance.

Hybrid organic–inorganic perovskite is one of the most promising candidates to replace state-of-art silicon to fabricate low cost solar cells. However, its instability, including intrinsic and operational instability, strongly hinders its real-life applications. Methylammonium (MA)-free, formamidinium (FA)-based perovskite doped by small A-site inorganic cations was developed to tackle the intrinsic instability issue, but the operational instability, especially against the applied electric field, induced by defect mediated ion migration remains a problem. In this work, we fabricate two types of MA-free perovskites, Rb0.05Cs0.1FA0.85PbI3 and Cs0.15FA0.85PbI3, and investigate the effect of Rb+ on the device performance and long-term stability. We find that even with incomplete incorporation, Rb+ cation can significantly improve the device performance. We reveal the defect-mediated cation and anion migration under electric field using cross-sectional secondary electron microscopy, X-ray photoelectron spectroscopy, and time-of-flight secondary ion mass spectrometry, and identify that Rb+ is more vulnerable compared to Cs+. By simply mixing the precursor solution before spin coating, we significantly reduce the defect states in both types of perovskite and improve the device stability against an electric field. The modified precursor solution provides the devices with Rb0.05Cs0.1FA0.85PbI3 and Cs0.15FA0.85PbI3 active layers that retain 68% and 92% of their initial PCE, respectively, over 30 days under N2 protection.