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Tin‐based perovskites are promising alternative absorber materials for lead‐free perovskite solar cells but need strategies to avoid fast tin (Sn) oxidation. Generally, this reaction can be slowed down by the addition of tin fluoride (SnF2) to the perovskite precursor solution, which also improves the perovskite layer morphology. Here, this work analyzes the spatial distribution of the additive within formamidinium tin triiodide (FASnI3) films deposited on top of poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) hole transporting layers. Employing time‐of‐flight secondary ion mass spectrometry and a combination of hard and soft X‐ray photoelectron spectroscopy, it is found that SnF2 preferably accumulates at the PEDOT:PSS/perovskite interface, accompanied by the formation of an ultrathin SnS interlayer with an effective thickness of ≈1.2 nm. [ABSTRACT FROM AUTHOR]

Passivating the defects and grain boundaries (GBs) of perovskite films at the interface by interface engineering is a promising route to achieve efficient and stable perovskite solar cells (PSCs). Herein, a new type of graphene, that is, hydrophobic graphene quantum dots (HGQDs) containing amide linkages, which consist of carbonyl and dodecyl amine groups, is successfully used as a bifunctional interface modifier to engineer the interface of the perovskite/hole transport layer. A comprehensive characterization including X‐ray photoelectron spectroscopy, Fourier‐transform photocurrent spectroscopy, Raman spectroscopy, photoluminescence spectroscopy, and space‐charge‐limited current measurements is performed to identify the underlying passivation mechanisms. It can be demonstrated that the HGQDs, due to the bifunctional groups containing N and O atoms, effectively passivate the uncoordinated Pb2+ ions at the perovskite film surface and GBs and consequently induce a lower trap state density. Moreover, HGQDs enhance the quality of the perovskite film which reduces the charge recombination at the interface. Therefore, the power conversion efficiency of PSCs treated with HGQDs is significantly increased from 16.00% to 18.30%, mainly based on the improved open‐circuit voltage and fill factor. Importantly, the HGQDs featuring hydrophobicity due to alkyl chains significantly enhance moisture stability. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) hybrid perovskites have attracted considerable attention due to their enormous structural and electronical variability, making this class of semiconductors interesting for photovoltaics, light-emitting diodes and lasers. 2D perovskites consist of sheets of bulky organic cations alternately sandwiched by layers of lead halide octahedra. The properties of these materials strongly depend on the thickness of the octahedra layers, defined by the number of octahedra sheets in a layer, n. Consequently, controlling the layer thickness purity (i.e. minimizing the spread in n) is important for any 2D perovskite thin film application. Here, we show that using rationally chosen solvent additives in the precursor solution offers a facile way to control the crystal disorder in 2D perovskites films. Our method leads to significantly reduced variation in n around the target value relative to films obtained by conventional fast-crystallization methods without solvent additives. The improved phase purity in optimized n = 2 and n = 3 films is verified by X-ray diffraction, UV-vis absorption, and photoluminescence measurements. Additionally, we find that 2D perovskite films with n≥ 2 arising from additive-assisted growth exhibit an unusual crystal orientation with the perovskite interlayers predominantly aligned parallel to the substrate, which we assign to the slow crystallization process induced by the lead-complexing solvent additives. Improved control over the phase purity translates into a better control of the optoelectronic properties of 2D perovskite films. Furthermore, the unusual horizontal crystal orientation of n = 2 and n = 3 films makes this family of tunable organic–inorganic perovskites promising for applications where lateral charge transport is desired, thus enlarging the potential for thin film-based applications of the 2D perovskites. [ABSTRACT FROM AUTHOR]

Abstract: Adding cesium (Cs) and rubidium (Rb) cations to FA0.83MA0.17Pb(I0.83Br0.17)3 hybrid lead halide perovskites results in a remarkable improvement in solar cell performance, but the origin of the enhancement has not been fully understood yet. In this work, time‐of‐flight, time‐resolved microwave conductivity, and thermally stimulated current measurements are performed to elucidate the impact of the inorganic cation additives on the trap landscape and charge transport properties within perovskite solar cells. These complementary techniques allow for the assessment of both local features within the perovskite crystals and macroscopic properties of films and full devices. Strikingly, Cs‐incorporation is shown to reduce the trap density and charge recombination rates in the perovskite layer. This is consistent with the significant improvements in the open‐circuit voltage and fill factor of Cs‐containing devices. By comparison, Rb‐addition results in an increased charge carrier mobility, which is accompanied by a minor increase in device efficiency and reduced current–voltage hysteresis. By mixing Cs and Rb in quadruple cation (Cs‐Rb‐FA‐MA) perovskites, the advantages of both inorganic cations can be combined. This study provides valuable insights into the role of these additives in multiple‐cation perovskite solar cells, which are essential for the design of high‐performance devices. [ABSTRACT FROM AUTHOR]

Solution-processed bulk heterojunction solar cells consisting of the previously developed dithienopyrrole containing A–D–A oligothiophenes (A = acceptor, D = donor unit) and [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) with power conversion efficiency up to 7.1% after solvent vapor annealing (SVA) are demonstrated. The influence of the position of the alkyl side chains attached to the thiophene units on the SVA, and the usage of either PC61BM or PC71BM as acceptor, is investigated in more detail by negative secondary ion mass spectrometry (SIMS), Kelvin probe force microscopy (KPFM), photoluminescence (PL), and grazing-incidence X-ray diffraction spectroscopy (GIWAXS). It was found that besides increased crystallinity and domain sizes, the active layers consisting of two different isomers which we will refer to in the following as isomer 1 or isomer 2 had different compositions after SVA treatment. In the former, a more or less homogeneously-mixed D:A blend was observed, whereas the latter showed a vertical gradient of PCBM in the active layer and much stronger phase segregation on the surface. These findings correlate well with the differences in solar cell performance of both isomers, before and after SVA. [ABSTRACT FROM AUTHOR]

The extension of a series of dithienopyrrole containing A-D-A oligothiophenes for application in solution-processed bulk heterojunction solar cells is described. Using solvent vapor annealing, power conversion efficiencies up to 6.1% are obtained. Exposure of the photoactive layer to chloroform vapor results in increased absorption and ordering of the donor:acceptor blend, as is evident from UV-vis absorption spectroscopy, X-ray diffraction (XRD) spectroscopy, and atomic force microscopy (AFM). The type and position of the solubilizing alkyl chains influences the dissolution, optical, and packing properties of the oligomers. However, despite subtle differences in molecular structure, all electron donors could be implemented in solar cells demonstrating power conversion efficiencies between 4.4 and 6.1%. Upon further optimization of these in-air, processed devices, it is expected that additional improvements in photovoltaic performance can be achieved. [ABSTRACT FROM AUTHOR]

Isomeric dicyanovinylene-terminated oligothiophenes 1 and 2 comprising a central dithienopyrrole (DTP) unit have been developed for solution-processed small molecule organic solar cells (SMOSCs) giving the highest power conversion efficiency of 4.8% for DTP-based oligomeric materials. [ABSTRACT FROM AUTHOR]

We report on the fabrication of highly efficient, semitransparent bulk heterojunction solar cells comprising poly[[9-(1-octylnonyl)-9h-carbazole-2,7-diyl]-2,5-thiophenediyl-2,1,3-benzothiadiazole-4,7-diyl-2,5-thiophenediyl] (PCDTBT) blended with [6,6]-phenyl-C71-butyric acid methyl (PC71BM) esters as active layer. As semitransparent cathode sputtered aluminum doped ZnO was used in combination with a sputter damage preventing, thin (8 nm) TiOx layer processed from solution and a sputtered aluminum interlayer (ALI). The short circuit current improves for thicker ALIs due to increased reflectance at the cathode leading to average efficiencies of 4.0% for semitransparent solar cells. Comparable results (3.9%) were achieved for devices comprising thick absorbers and thin ALIs. [ABSTRACT FROM AUTHOR]

We investigate the influence of solution-processed cesium fluoride (CsF) interlayers on the performance of inverted polymer solar cells comprising a blend of poly(3-hexylthiophene-2,5-diyl):[6,6]-phenyl C61-butyric acid methyl ester. The thickness of the CsF layer is optimized in terms of current-voltage characteristics by a variation of the solid content in solution. Capacitance-voltage characteristics reveal a shift of the built-in voltage at the cathode interface by about 0.3 V as compared to devices without a CsF layer, giving rise to an increase in open-circuit voltage by the same value. The vertical distribution of Cs+ and F+ ions is studied by secondary ion mass spectroscopy, indicating a strong diffusion of the alkaline fluoride into the organic layer stack. [ABSTRACT FROM AUTHOR]

Highly efficient organic solar cells with all-solution-processed low-cost transparent front contacts based on highly conductive formulations of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) are reported, demonstrating the feasibility of replacing the costly conventional vacuum-deposited indium-tin-oxide contacts by means of simple printing techniques. For small cell areas, the relatively high sheet resistances were found to be less detrimental to the photovoltaic performance than the deficiencies in the transparency of the contact layer. [ABSTRACT FROM AUTHOR]

Based on the well-known beneficial effect of a thin LiF layer underneath Al contacts for organic solar cells, a comparative study of interlayers made from the alkaline fluorides LiF, NaF, and KF is presented for polymer bulk heterojunction solar cells. The overall suitability of these materials and the underlying mechanisms are discussed. While an improvement in cell efficiency up to a factor of 2 can be reached with all three fluorides, the necessary thickness of the interlayer for maximum improvement is smallest for NaF and largest for LiF, suggesting the alternative use of NaF instead of LiF. [ABSTRACT FROM AUTHOR]

The sputter deposition technique is usually avoided for organic solar cells, despite its technological advantages, because it may potentially damage the organic absorber layer. The consequences of sputtering on device performance-presumably related to changes in the absorber morphology and defect distribution near the interface-are discussed. Despite its negative influence on as-deposited samples, sputtering in combination with thermal annealing can actually be beneficial for pure aluminum contacts, leading to efficiencies even better than those of cells with thermally evaporated cathodes, mainly due to an enhanced open-circuit voltage. [ABSTRACT FROM AUTHOR]