Photovoltaic technology requires light-absorbing materials that are highly efficient, lightweight, low cost and stable during operation. Organolead halide perovskites constitute a highly promising class of materials, but suffer limited stability under ambient conditions without heavy and costly encapsulation. Here, we report ultrathin (3 μm), highly flexible perovskite solar cells with stabilized 12% efficiency and a power-per-weight as high as 23 W g(-1). To facilitate air-stable operation, we introduce a chromium oxide-chromium interlayer that effectively protects the metal top contacts from reactions with the perovskite. The use of a transparent polymer electrode treated with dimethylsulphoxide as the bottom layer allows the deposition-from solution at low temperature-of pinhole-free perovskite films at high yield on arbitrary substrates, including thin plastic foils. These ultra-lightweight solar cells are successfully used to power aviation models. Potential future applications include unmanned aerial vehicles-from airplanes to quadcopters and weather balloons-for environmental and industrial monitoring, rescue and emergency response, and tactical security applications.

Instrumentation: 1 H NMR and 13 C NMR spectra were measured in deuterated chloroform using a Bruker DRX 400 and a Bruker AC 250. Chemical shifts (δ values) are given in part per million with tetramethylsilane as an internal standard. Elemental analysis was performed on a CHNS-932 Automat Leco. Differential scanning calorimetry (DSC) measurements were carried out on a Mettler DSC 30 with a cell purged with nitrogen. Calibration for temperature and enthalpy changes was performed using an Indium standard. The temperature was changed between 0 and 250 o C with a heating/cooling rate of 10 K/min. In total two heating-cooling cycles were performed on each sample. Thermogravimetric analysis (TGA) was performed on a Mettler TA-300-thermal analyzer operating under air atmosphere. The samples were heated from 0 to 700 °C with a heating rate of 10 K/min. Gel permeation chromatography was performed on a set of Knauer using THF as eluent and polystyrene as standard. The absorption spectra were recorded in dilute chloroform solution (c ≈ 10-6 mol l-1) on a Perkin-Elmer UV/VIS-NIR Spectrometer Lambda 19. Quantum-corrected emission spectra were measured in dilute chloroform solution with a LS 50 luminescence spectrometer (Perkin-Elmer). The solution photoluminescence quantum yields were calculated either according to Demas and Crosby against quinine sulfate in 0.1 N sulfuric acid as a standard (Φ f = 55%) 1 or in ethanol against rhodamine 6G standard (Φ f = 95%). Thin film (from CHCl 3 solution) absorption and emission spectra were measured with a Hitachi F-4500 Fluorescence Spectrophotometer. Their absolute photoluminescence quantum yields were measured in an intergrating sphere. The absorption spectra of thin film from chlorobenzene solution were recorded on Varian UV/Vis spectrophotometer and the corresponding emission spectra were recorded on a home-built photoluminescence setup. Thin films were spin coated on glass substrates using chlorobenzene based solutions (0.6-0.8 wt %). Infrared spectroscopy was recorded on a Nicolet Impact 400. Cyclic voltammetry (CV) was performed with a PA4 polarographic analyzer (Laboratory Instruments, Prague, CZ) with a

We report on the fabrication and opto-electronic characterization of solution-processed planar heterojunction perovskite solar cells based on methylammonium (MA) lead halide derivatives, MAPbI3−xYx(Y = Cl, Br, I).

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