The area of thin-film photovoltaics has been overwhelmed by organometal halide perovskites. Unfortunately, serious stability concerns arise with perovskite solar cells. For example, methyl-ammonium lead iodide is known to decompose in the presence of water and, more severely, even under inert conditions at elevated temperatures. Here, we demonstrate inverted perovskite solar cells, in which the decomposition of the perovskite is significantly mitigated even at elevated temperatures. Specifically, we introduce a bilayered electron-extraction interlayer consisting of aluminium-doped zinc oxide and tin oxide. We evidence tin oxide grown by atomic layer deposition does form an outstandingly dense gas permeation barrier that effectively hinders the ingress of moisture towards the perovskite and—more importantly—it prevents the egress of decomposition products of the perovskite. Thereby, the overall decomposition of the perovskite is significantly suppressed, leading to an outstanding device stability.
Metal-halide perovskite semiconductors are of tremendous interest for a variety of applications. Only recently, solar cells based on a representative of this family have been certified with an efficiency in excess of 24%.[1] Aside from their remarkable success in photovoltaics, metal-halide perovskites are also highly promising as light emitters, e.g., in light-emitting diodes (LEDs) or lasers. [2][3][4] LEDs based on the fruit-fly of these compounds, i.e., methylammonium lead iodide (CH 3 NH 3 PbI 3 or MAPbI 3 ), and other related perovskites have been demonstrated with continuously increasing efficiency. [5][6][7] For lasers, there is the vision that perovskites may overcome/avoid the typical limitations and loss mechanisms present in organic gain media, such as triplet-singlet annihilation or absorption due to triplet excitons and Cesium lead halide perovskites are of interest for light-emitting diodes and lasers. So far, thin-films of CsPbX 3 have typically afforded very low photoluminescence quantum yields (PL-QY < 20%) and amplified spontaneous emission (ASE) only at cryogenic temperatures, as defect related nonradiative recombination dominated at room temperature (RT). There is a current belief that, for efficient light emission from lead halide perovskites at RT, the charge carriers/excitons need to be confined on the nanometer scale, like in CsPbX 3 nanoparticles (NPs).Here, thin films of cesium lead bromide, which show a high PL-QY of 68% and low-threshold ASE at RT, are presented. As-deposited layers are recrystallized by thermal imprint, which results in continuous films (100% coverage of the substrate), composed of large crystals with micrometer lateral extension. Using these layers, the first cesium lead bromide thin-film distributed feedback and vertical cavity surface emitting lasers with ultralow threshold at RT that do not rely on the use of NPs are demonstrated. It is foreseen that these results will have a broader impact beyond perovskite lasers and will advise a revision of the paradigm that efficient light emission from CsPbX 3 perovskites can only be achieved with NPs.
The electronic structure of a large sample set of CH3 NH3 PbI3 -based perovskites is studied. Combined investigations by UV/X-ray photoelectron spectroscopy and X-ray diffraction reveal that interstitials present in the film lead to changes in the occupied density of states close to the valence band, which in turn influences the performance of solar cells. Changes in elemental composition tune the ionization energy of the perovskite film by almost 1 eV without introducing significant amounts of gap states.
Photonic nanostructures are created in organo-metal halide perovskites by thermal nanoimprint lithography at a temperature of 100 °C. The imprinted layers are significantly smoothened compared to the initially rough, polycrystalline layers and the impact of surface defects is substantially mitigated upon imprint. As a case study, 2D photonic crystals are shown to afford lasing with ultralow lasing thresholds at room temperature.
Semitransparent perovskite solar cells (PSCs) are of interest for application in tandem solar cells and building-integrated photovoltaics. Unfortunately, several perovskites decompose when exposed to moisture or elevated temperatures. Concomitantly, metal electrodes can be degraded by the corrosive decomposition products of the perovskite. This is even the more problematic for semitransparent PSCs, in which the semitransparent top electrode is based on ultrathin metal films. Here, we demonstrate outstandingly robust PSCs with semitransparent top electrodes, where an ultrathin Ag layer is sandwiched between SnO x grown by low-temperature atomic layer deposition. The SnO x forms an electrically conductive permeation barrier, which protects both the perovskite and the ultrathin silver electrode against the detrimental impact of moisture. At the same time, the SnO x cladding layer underneath the ultra-thin Ag layer shields the metal against corrosive halide compounds leaking out of the perovskite. Our semitransparent PSCs show an efficiency higher than 11% along with about 70% average transmittance in the near-infrared region (λ > 800 nm) and an average transmittance of 29% for λ = 400-900 nm. The devices reveal an astonishing stability over more than 4500 hours regardless if they are exposed to ambient atmosphere or to elevated temperatures.
Thermal management in devices like solar cells, light-emitting diodes, and lasers based on hybrid halide perovskite thin films is expected to be of paramount importance for optimal performance and reliability. As of yet, experimental data of thermal properties of non-iodine-based hybrid halide perovskites is very scarce. Here the thermal conductivity of methylammonium lead halide perovskite (CH3NH3PbX3 X= I, Br, and Cl) single crystals and thin films is analyzed by scanning near-field thermal microscopy. The thermal conductivity of CH3NH3PbX3 single crystals with X= I, Br, and Cl is found to be 0.34 ± 0.12, 0.44 ± 0.08, and 0.50 ± 0.05 W/(mK) at room temperature, respectively. Strikingly, similar thermal conductivities are determined for the corresponding thin-film samples. The thermal conductivity of MAPbI3 in the cubic phase (T > 55 °C) increases to (1.1 ± 0.1) W/(mK). In addition, the temperature dependence of the thermal conductivities and of thermal expansion coefficients of MAPbI3 around the phase transition from the tetragonal to cubic phase is presented.
Hybrid perovskite semiconductors hold great promise as low‐cost, yet high performance gain media for lasers. Distributed feedback (DFB) resonator structures are a key to unlock low laser threshold levels, which are essential on the way to the first electrically operated perovskite laser diode. Here, the first DFB lasers based on methylammonium lead bromide (MAPbBr3) thin films, with a linear photonic grating imprinted into the MAPbBr3 active layers is presented. High‐Q Bragg resonator gratings with a periodicity of 300 nm are directly patterned by thermal nanoimprinting into thin films of MAPbBr3 at a temperature as low as 100 °C. A notable effect of the imprinting process is a substantial flattening of the initially very rough polycrystalline perovskite layers to layers consisting of large crystals on the order of tens of microns with a surface roughness of 0.6 nm. The smooth surface affords a significantly lowered threshold for the onset of amplified spontaneous emission due to reduced scattering. In optically pumped DFB laser structures, very low lasing thresholds of 3.4 µJ cm−2 are achieved. It is foreseen that these results will influence research on perovskite‐based optoelectronic devices beyond lasers, e.g., light emitting diodes and solar cells.
Corrosive precursors used for the preparation of organic-inorganic hybrid perovskite photoactive layers prevent the application of ultrathin metal layers as semitransparent bottom electrodes in perovskite solar cells (PVSCs). This study introduces tin-oxide (SnO ) grown by atomic layer deposition (ALD), whose outstanding permeation barrier properties enable the design of an indium-tin-oxide (ITO)-free semitransparent bottom electrode (SnO /Ag or Cu/SnO ), in which the metal is efficiently protected against corrosion. Simultaneously, SnO functions as an electron extraction layer. We unravel the spontaneous formation of a PbI interfacial layer between SnO and the CH NH PbI perovskite. An interface dipole between SnO and this PbI layer is found, which depends on the oxidant (water, ozone, or oxygen plasma) used for the ALD growth of SnO . An electron extraction barrier between perovskite and PbI is identified, which is the lowest in devices based on SnO grown with ozone. The resulting PVSCs are hysteresis-free with a stable power conversion efficiency (PCE) of 15.3% and a remarkably high open circuit voltage of 1.17 V. The ITO-free analogues still achieve a high PCE of 11%.
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