Interfacial Modification for High-Efficiency Vapor-Phase-Deposited Perovskite Solar Cells Based on a Metal Oxide Buffer Layer

Vacuum deposition is one of the most technologically relevant techniques for the fabrication of perovskite solar cells. The most efficient vacuum-based devices rely on doped organic contacts, compromising the long-term stability of the system. Here, we introduce an inorganic electron-transporting material to obtain power conversion efficiencies matching the best performing vacuum-deposited devices, with open-circuit potential close to the thermodynamic limit. We analyze the leakage current reduction and the interfacial recombination improvement upon use of a thin (<10 nm) interlayer of C₆₀, as well as a more favorable band alignment after a bias/ultraviolet light activation process. This work presents an alternative for organic contacts in highly efficient vacuum-deposited perovskite solar cells

Ultrathin Ammonium Heptamolybdate Films as Efficient Room-Temperature Hole Transport Layers for Organic Solar Cells

Ammonium heptamolybdate (NH₄)₆Mo₇O₂₄·4H₂O (AHM) and its peroxo derivatives are analyzed as solution-processed room temperature hole transport layer (HTL) in organic solar cells. Such AHM based HTLs are investigated in devices with three different types of active layers, i.e., solution-processed poly­(3-hexylthiophene)/[6,6]-phenyl C₆₁-butyric acid methyl ester­(P3HT/PC₆₀BM), poly­[<i>N</i>-9′-heptadecanyl-2,7-carbazole-<i>alt</i>-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole)]/[6,6]-phenyl C₇₀-butyric acid methyl ester­(PCDTBT/PC₇₀BM) and evaporated small molecule chloro­(subphthalocyaninato)­boron­(III) (SubPc)/C₆₀. By virtue of their high work functions, AHM based HTLs outperform the commonly used poly­(3,4-ethylenedioxythiophene):polystyrenesulfonate (PEDOT:PSS) HTL for devices employing deep HOMO level active materials. Moreover, devices using AHM based HTLs can achieve higher short circuit current (<i>J</i>_sc) than the ones with evaporated molybdenum oxide­(eMoO₃), and thus better power conversion efficiency (PCE). In addition, P3HT/PC₆₀BM devices with AHM based HTLs show air stability comparable to those with eMoO₃, and much better than the ones with PEDOT:PSS

Effect of Fluorination on the Properties of a Donor–Acceptor Copolymer for Use in Photovoltaic Cells and Transistors

Two novel indacenodithiophene (IDT) based donor–acceptor conjugated polymers for use in organic field effect transistors and photovoltaic devices are synthesized and characterized. The effect of inclusion of two fluorine atoms on the acceptor portion of the polymer is thoroughly investigated via a range of techniques. The inductively withdrawing and mesomerically donating properties of the fluorine atoms result in a decrease of the highest occupied molecular orbital (HOMO), with little effect on the lowest unoccupied molecular orbital (LUMO) as demonstrated through density functional theory (DFT) analysis. Inclusion of fluorine atoms also leads to a potentially more planar backbone through inter and intrachain interactions. Use of the novel materials in organic field effect transistor (OFET) and organic photovoltaic (OPV) devices leads to high mobilities around 0.1 cm²/(V s) and solar cell efficiencies around 4.5%

Improved Photovoltaic Performance of a Semicrystalline Narrow Bandgap Copolymer Based on 4<i>H</i>-Cyclopenta[2,1-<i>b</i>:3,4-<i>b</i>′]dithiophene Donor and Thiazolo[5,4-<i>d</i>]thiazole Acceptor Units

A solution processable narrow bandgap polymer composed of alternating 2,5-dithienylthiazolo­[5,4-<i>d</i>]­thiazole and asymmetrically alkyl-substituted 4<i>H</i>-cyclopenta­[2,1-<i>b</i>:3,4-<i>b</i>′]­dithiophene units (<b>PCPDT-DTTzTz</b>) was synthesized by Suzuki polycondensation and the donor–acceptor copolymer was thoroughly characterized. Thermal analysis and X-ray diffraction studies disclosed the semicrystalline nature of the material. When blended with PC₇₁BM and integrated in bulk heterojunction organic solar cells, a moderate power conversion efficiency of 2.43% under AM 1.5 G (100 mW/cm²) conditions was obtained. However, upon purification of the semiconducting copolymer by preparative size exclusion chromatography, a noticeable rise in power conversion efficiency to 4.03% was achieved. The purified polymer exhibited a relatively high field-effect carrier mobility of 1.0 × 10^–3 cm²/(V s). The active layer morphology was explored by atomic force microscopy and transmission electron microscopy studies, showing phase segregation on the nanometer scale

Isostructural, Deeper Highest Occupied Molecular Orbital Analogues of Poly(3-hexylthiophene) for High-Open Circuit Voltage Organic Solar Cells

We present the synthesis and characterization of two novel thiazole-containing conjugated polymers (<b>PTTTz</b> and <b>PTTz</b>) that are isostructural to poly­(3-hexylthiophene) (P3HT). The novel materials demonstrate optical and morphological properties almost identical to those of P3HT but with HOMO and LUMO levels that are up to 0.45 eV deeper. An intramolecular planarizing nitrogen–sulfur nonbonding interaction is observed, and its magnitude and origin are discussed. Both materials demonstrate significantly greater open circuit voltages than P3HT in bulk heterojunction solar cells. <b>PTTTz</b> is shown to be an extremely versatile donor polymer that can be used with a wide variety of fullerene acceptors with device efficiencies of up to 4.5%. It is anticipated that this material could be used as a high-open circuit voltage alternative to P3HT in organic solar cells