Deposition of perovskite films by antisolvent engineering is a highly common method employed in perovskite photovoltaics research. Herein, we report on a general method that allows for the fabrication of highly efficient perovskite solar cells by any antisolvent via manipulation of the antisolvent application rate. Through detailed structural, compositional, and microstructural characterization of perovskite layers fabricated by 14 different antisolvents, we identify two key factors that influence the quality of the perovskite layer: the solubility of the organic precursors in the antisolvent and its miscibility with the host solvent(s) of the perovskite precursor solution, which combine to produce rate-dependent behavior during the antisolvent application step. Leveraging this, we produce devices with power conversion efficiencies (PCEs) that exceed 21% using a wide range of antisolvents. Moreover, we demonstrate that employing the optimal antisolvent application procedure allows for highly efficient solar cells to be fabricated from a broad range of precursor stoichiometries.

A dual interfacial modification simultaneously improves all photovoltaic parameters of inverted perovskite solar cells.

Engineering two-dimensional (2D) / three-dimensional (3D) perovskites has emerged as an attractive route to efficient and durable perovskite solar cells. Beyond improving the surface stability of the 3D layer and acting as a trap passivation agent, the exact function of 2D/3D device interface remains vague. Here, we provide evidence that 2D/3D perovskite interface that forms a p-n junction is capable to reduce the electron density at the hole-transporting layer interface and ultimately suppress interfacial recombination. By a novel ultraviolet photoelectron spectroscopy (UPS) depth-profiling technique, we show that engineering of the 2D organic cations, in this case by simply varying the halide counter ions in thiophene methylammonium-salts, modifies the 2D/3D perovskite energy alignment. These measurements enable the true identification of the energetic across the 2D/3D interface, so far unclear. When integrated in solar cells, due to the electron blocking nature of the 2D layer, the optimized 2D/3D structures suppress the interfacial recombination losses, leading to opencircuit voltage (VOC) which approaches the potential internal Quasi-Fermi Level Splitting (QFLS) voltage of the perovskite absorber. The devices exhibit an improved fill factor (FF) driven by the enhanced hole extraction efficiency and reduced electron density at the 2D/3D interface. We thus identify the essential parameters and energetic alignment scenario required for 2D/3D perovskite systems in order to surpass the current limitations of hybrid perovskite solar cell performances.Understanding and exploiting interfacial physics is key in perovskite solar cell engineering and optimization. 1,2 That is especially true when interface losses play a dominant role and complex interface functionalization is essential to minimize them. In the field of hybrid perovskite engineering, much attention has been lately focused on multi-dimensional perovskite interfaces consisting of a wider band gap layered (namely, two dimensional-2D) perovskite deposited between the bulk 3D perovskite and the hole transporting layer (HTL) in a standard mesoporous configuration. [3][4][5][6][7][8][9] Such configuration is currently among the most effective strategies to enhance both the efficiency and stability of perovskite solar cells. 3,10,11 It is generally considered that the 2D perovskite acts as both an efficient mean to passivate the surface traps (leading to reduced defect recombination) and an electron blocking layer due to its wider band gap. [12][13][14][15] However, despite these empirical observations, the energetic alignment at the interface and the relative function of the 2D/3D interface is only qualitatively depicted with a only a partial understanding of these

No abstract

Efficient, stable, and solution-based n-doping of semiconducting single-walled carbon nanotubes (SWCNTs) is highly desired for complementary circuits but remains a significant challenge. Here, we present 1,2,4,5-tetrakis(tetramethylguanidino)benzene (ttmgb) as a strong two-electron donor that enables the fabrication of purely n-type SWCNT field-effect transistors (FETs). We apply ttmgb to networks of monochiral, semiconducting (6,5) SWCNTs that show intrinsic ambipolar behavior in bottom-contact/top-gate FETs and obtain unipolar n-type transport with 3-5-fold enhancement of electron mobilities (approximately 10 cm V s), while completely suppressing hole currents, even at high drain voltages. These n-type FETs show excellent on/off current ratios of up to 10, steep subthreshold swings (80-100 mV/dec), and almost no hysteresis. Their excellent device characteristics stem from the reduction of the work function of the gold electrodes via contact doping, blocking of hole injection by ttmgb on the electrode surface, and removal of residual water from the SWCNT network by ttmgb protonation. The ttmgb-treated SWCNT FETs also display excellent environmental stability under bias stress in ambient conditions. Complementary inverters based on n- and p-doped SWCNT FETs exhibit rail-to-rail operation with high gain and low power dissipation. The simple and stable ttmgb molecule thus serves as an example for the larger class of guanidino-functionalized aromatic compounds as promising electron donors for high-performance thin film electronics.

At a current value of 25.5%, perovskites have reached some of the highest power conversion efficiencies of all single-junction solar cell devices. Researchers, however, are questioning their readiness for the commercial market, citing reasons of the toxicity of the lead-based active layer and instability. Closer examination of the life cycle of perovskite solar cells reveals that there are more areas than just these which should be addressed in order to bring an environmentally friendly and sustainable technology to global use. In this review, we discuss these issues. Life cycle analyses show that high temperature processes, heavy use of organic solvents, and extensive use of certain materials can have high up and downstream consequences in terms of emissions, human and ecotoxicity. We further bring attention to the toxicity of the perovskites themselves, where the most direct analyses suggest that the lead cannot be considered totally safe, despite its small quantity and that replacements such as tin may be more toxic in certain scenarios. As a way to reduce the negative environmental impact, we highlight ways in which researchers have used encapsulation and recycling to extend the life of the entire unit and its components and to prevent lead leakage. We hope this review directs researchers toward new strategies to introduce a clean solar technology to the world.

Reducing the size of a material, from a bulk solid to a nanomaterial, may lead to drastic changes of various properties including reactivity and optical properties. Chemical reactivity is often increased due to the nanomaterial’s higher effective surface area, while confinement and geometric effects lead to systematic changes in optical properties. Here, we investigate the size-dependent properties of Ni2P2S6 nanosheets that were obtained from liquid phase exfoliation in N-cyclohexyl-2-pyrrolidone. The as-obtained stock dispersion was size-selected by liquid cascade centrifugation resulting in fractions with distinct size and thickness distributions, as quantified by statistical atomic force microscopy. Raman, TEM, XRD, and XPS characterization revealed that the exfoliated flakes have good crystallinity and high structural integrity across all sizes. The optical extinction and absorbance spectra systematically change with the lateral dimensions and layer number, respectively. Linking these changes to nanosheet dimensions allows us to establish quantitative metrics for size and thickness from optical properties. To gain insights into the environmental stability, extinction/absorbance behavior was followed as a function of time at different storage temperatures. Degradation is observed following first-order kinetics, and activation energies were extracted from the temperature dependent data. The decomposition is due to oxidation which appears to occur both at edges and on the basal plane.

Thin‐film deposition by thermal evaporation offers many advantages, yet in the field of perovskite photovoltaics solution‐processed devices significantly outperform those fabricated by thermal evaporation. Here, high‐quality γ‐CsPbI3 perovskite layers by coevaporation of PbI2 and CsI with a small amount of phenylethylammonium iodide (PEAI) are deposited. It is demonstrated that the addition of PEAI into the perovskite layers leads to a preferred crystal orientation and a far improved microstructure, with columnar domains that protrude throughout the film's thickness. This is accompanied by a reduced density of defects as evidenced by the increase in photoluminescence and decrease in Urbach energy as compared to reference CsPbI3 films. Photovoltaic devices based on the PEAI containing perovskite layers reach up to 15% in power conversion efficiency, thus surpassing not only the performance of reference CsPbI3 devices, but also that of most solution‐processed PEAI containing inorganic CsPbX3 (X = Cl, Br, I) perovskite solar cells. Importantly, encapsulated thermally evaporated perovskite devices maintain their performance for over 215 days, demonstrating the stabilizing effect of PEAI on thermally evaporated CsPbI3.