Perovskite solar cells (PSCs) have reached an impressive efficiency over 23%. One of its promising characteristics is the low-cost solution printability, especially for flexible solar cells. However, printing large area uniform electron transport layers on rough and soft plastic substrates without hysteresis is still a great challenge. Herein, we demonstrate slot-die printed high quality tin oxide films for high efficiency flexible PSCs. The inherent hysteresis induced by the tin oxide layer is suppressed using a universal potassium interfacial passivation strategy regardless of fabricating methods. Results show that the potassium cations, not the anions, facilitate the growth of perovskite grains, passivate the interface, and contribute to the enhanced efficiency and stability. The small size flexible PSCs achieve a high efficiency of 17.18% and large size (5 × 6 cm2) flexible modules obtain an efficiency over 15%. This passivation strategy has shown great promise for pursuing high performance large area flexible PSCs.

The hot-phonon bottleneck effect in lead-halide perovskites (APbX3) prolongs the cooling period of hot charge carriers, an effect that could be used in the next-generation photovoltaics devices. Using ultrafast optical characterization and first-principle calculations, four kinds of lead-halide perovskites (A=FA+/MA+/Cs+, X=I−/Br−) are compared in this study to reveal the carrier-phonon dynamics within. Here we show a stronger phonon bottleneck effect in hybrid perovskites than in their inorganic counterparts. Compared with the caesium-based system, a 10 times slower carrier-phonon relaxation rate is observed in FAPbI3. The up-conversion of low-energy phonons is proposed to be responsible for the bottleneck effect. The presence of organic cations introduces overlapping phonon branches and facilitates the up-transition of low-energy modes. The blocking of phonon propagation associated with an ultralow thermal conductivity of the material also increases the overall up-conversion efficiency. This result also suggests a new and general method for achieving long-lived hot carriers in materials.

Carbon dots are cost-effective, environmental friendly, and biocompatible nanoparticles with many potential applications in optoelectronics and biophotonics. Their dual fluorescence bands were observed and could be attributed to core and surface state emission. We also conduct temperature-dependent fluorescence measurements from cryogenic to room temperatures. The dual emission bands exhibit similar temperature dependence. The strong electron–electron interactions and weak electron–phonon interactions could account for the very broad photoluminescence (PL) band even at 77 K. Our experimental results also suggest that carbon dots exhibit similar temperature behavior as metallic quantum dots (nanoclusters) but are different from inorganic semiconductor quantum dots. Here, for the first time, we present the temperature-dependent spectroscopic results to shed some light on the presently unclear fluorescence mechanism.

its rate reading is inevitably affected by the MAI sublimation during co-deposition.Another advantage of perovskite solar cells is the ability to tune the bandgap by mixing the halide anions. This applies to Cs mixed halide [ 18,19 ] as well as MA or FA lead mixed halides, enabling optimization of solar spectrum absorption for both single-junction and tandem solar cells.In this study, we report a dual source thermal evaporation process to deposit mixed halide CsPbIBr 2 perovskite absorber with a bandgap of 2.05 eV. This material has a potential to be used in a three-junction tandem as the quality of the material and therefore voltage of the device further improves. Inorganic CsI and PbBr 2 precursors are simultaneously evaporated onto a compact TiO 2 layer (c-TiO 2 ) on FTO glass substrates. Postannealing is carried out on a hot plate in a glove box to enable the full crystallization of the CsPbIBr 2 perovskite. A series of experiments investigating the effect of postanneal conditions on the crystalline structure is conducted in this work. Films achieve best quality in terms of crystallinity, thickness uniformity, and grain size uniformity when the samples are annealed at 250° for 10 min. Aiming at a simple architecture and an organiccomponent-free device, we fabricated a hole transport material (HTM) free planar Glass/FTO/c-TiO 2 /CsPbIBr 2 /Au solar cell, fi rst of its kind, with a PCE of 4.7%, a short-circuit current density ( J SC ) of 8.7 mA cm −2 , an open-circuit voltage ( V OC ) of 959 mV, and a fi ll factor (FF) of 56% under reverse scan, while PCE = 3.7%, J SC = 8.7 mA cm −2 , V OC = 818 mV and FF = 52% under forward scan.As described in the Experimental Section, the CsPbIBr 2 samples were prepared by evaporating the same molar quantity of CsI and PbBr 2 onto the substrates. The chemical composition of the samples was evaluated by X-ray photoelectron spectroscopy (XPS). The atomic ratio of Pb/Cs and Br/I was estimated to be 1.1 and 2.3, respectively, which is in good agreement with the CsPbIBr 2 composition. The XPS spectra are shown in Figure S1 in the Supporting Information. An Energy-dispersive X-ray spectroscopy (EDS) measurement at 15 kV was also carried out by a 20 µm line scan of the CsPbIBr 2 fi lm showing the atomic ratios of Pb/Cs and Br/I to be 1.2 and 1.94, respectively. The EDS spectra are shown in Figure S2 in the Supporting Information. One reason for the deviation between EDS and XPS results is the difference in accuracy between the measurements (XPS, ±5%, EDS, ±15%). It is also noted that the XPS carried out measures of the elemental composition of about 10 nm in depth from the surface. For bulk measurement, Ar ion etching will be required causing damage to the CsPbIBr 2 fi lm. Given the uniform column grains formed from the bottom to the surface of the CsPbIBr 2 fi lm as shown in Figure 5 a, The emergence of organic-inorganic hybrid halides perovskite solar cells has generated enormous interests in the photovoltaic research community. Due to their excellent optical absorption, good car...

Ultralow trap densities, exceptional optical and electronic properties have been reported for lead halide perovskites single crystals; however, ambiguities in basic properties, such as the band gap, and the electronic defect densities in the bulk and at the surface prevail. Here, we synthesize single crystals of methylammonium lead bromide (CH3NH3PbBr3), characterise the optical absorption and photoluminescence and show that the optical properties of single crystals are almost identical to those of polycrystalline thin films. We observe significantly longer lifetimes and show that carrier diffusion plays a substantial role in the photoluminescence decay. Contrary to many reports, we determine that the trap density in CH3NH3PbBr3 perovskite single crystals is 1015 cm−3 , only one order of magnitude lower than in the thin films. Our enhanced understanding of optical properties and recombination processes elucidates ambiguities in earlier reports, and highlights the discrepancies in the estimation of trap densities from electronic and optical methods.

The past two years have seen the uniquely rapid emergence of a new class of solar cell based on organic–inorganic halide perovskite. Although less explored than its tri-iodide counterparts, CH3NH3PbBr3 has a larger bandgap of 2.3 eV with a higher voltage potential that is suitable for tandem solar cell applications. In this paper, we report a vapor-assisted method for depositing and fully crystallizing CH3NH3PbBr3 film on mesoporous TiO2 with good coverage. CH3NH3PbBr3 fabricated using this method has demonstrated long carrier diffusion length (>1 μm) as estimated by transient photoluminescence-quenching measurements. We demonstrate solar cells fabricated using such films and spiro-OMeTAD as the hole transport layer with an averaged (from forward and reverse scans) conversion efficiency of 8.7%, V oc of 1.45 V, J sc of 9.75 mA/cm2, and fill factor of 61.5%.

The defect density and relaxation rate in organic–inorganic perovskites dominate the carrier recombination dynamics and thus PL intensity exhibits super-linear increase with increasing excitation.

The {010} and {110} crystal facets of monoclinic bismuth vanadate (m-BiVO4) has been demonstrated to be the active reduction and oxidation sites, respectively. Here, we show using dual-faceted m-BiVO4 with distinctly different dominant exposed facets, one which is {010}-dominant and the other {110}-dominant, contrary to prediction, the former m-BiVO4 exhibits superior photooxidation activities. The population of photogenerated electrons and holes on the surface are revealed to be proportional to the respective surface areas of {010} and {110} exposed on m-BiVO4, as evidenced by steady-state photoluminescence (PL) measurements in the presence of charge scavengers. The better photoactivity of {010}-dominant m-BiVO4 is attributed to prompt electron transfer facilitated by the presence of more photogenerated electrons on the larger {010} surface. Additionally, the greater extent of electron trapping in {110}-dominant m-BiVO4 also deteriorates its photoactivity by inducing electron-hole pair recombination.