Thin-film photovoltaics is a promising technology for low-cost and sustainable renewable energy sources. Organic-inorganic (hybrid) lead halide perovskite solar cells have recently aroused wide interest in photovoltaic applications because of their impressive power conversion efficiencies (PCEs), now exceeding 21%. [1][2][3] Importantly, the perovskite thin-film absorber can be deposited using low-cost and abundant starting materials, hence with a large potential for the preparation of inexpensive photovoltaic devices. 4 The high PCEs are the result of the very high absorption coefficient and mobilities of the photogenerated electrons and holes

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We demonstrate low-voltage inverted transparent vacuum deposited organic light-emitting diodes employing an indium-tin-oxide coated glass substrate directly as cathode and a semitransparent top Au thin film as anode. The devices comprise an intrinsic 8-tris-hydroxyquinoline aluminum (Alq3) emitting layer sandwiched in between n- and p-doped charge transport layer with appropriate blocking layers. They exhibit low driving voltages (∼4 V for a luminance of ∼100 cd/m2). The devices are about 50% transparent in the Alq3 emission region and emit green light from both sides with a total external current efficiency of about 2.5 cd/A.

Using the recently developed organic semiconductor, 2,9-didecyldinaphtho[2,3-b:2 0 ,3 0 -f]thieno [3,2-b]thiophene (C 10 -DNTT), we have fabricated organic thin-film transistors and ring oscillators on flexible polymeric substrates. By utilizing a gate dielectric with a small thickness (5.3 nm) and a large capacitance (800 nF cm À2 ), the transistors can be operated with relatively low voltages of about 2 to 3 V. To improve the charge exchange between the organic semiconductor and the gold source and drain contacts, a thin layer of a non-alkylated organic semiconductor (DNTT) sandwiched between two thin layers of a strong organic dopant (NDP-9) was inserted between the C 10 -DNTT and the gold contacts. The optimized transistors have a field-effect mobility of 4.3 cm 2 V À1 s À1 , an on/off current ratio of 10 8 , and a subthreshold swing of 68 mV per decade. The ring oscillators have a signal propagation delay of 5 ms per stage at a supply voltage of 3 V, making these the fastest organic circuits at supply voltages below 7 V reported to date.

Molecular doping is a key technique for fl exible and low-cost organic complementary semiconductor technologies that requires both effi cient and stable p-and n-type doping. However, in contrast to molecular p-dopants, highly effi cient n-type dopants are commonly sensitive to rapid degradation in air due to their low ionization energies ( IE s) required for electron donation, e.g., IE = 2.4 eV for tetrakis(1,3,4,6,7,8-hexahydro-2H -pyrimido[1,2-a ]pyrimidinato) ditungsten(II) (W 2 (hpp) 4 ). Here, the air stability of various host:W 2 (hpp) 4 combinations is compared by conductivity measurements and photoemission spectroscopy. A partial passivation of the n-doping against degradation is found, with this effect identifi ed to depend on the specifi c energy levels of the host material. Since host-W 2 (hpp) 4 electronic wavefunction hybridization is unlikely due to confi nement of the dopant highest occupied molecular orbital (HOMO) to its molecular center, this fi nding is explained via stabilization of the dopant by single-electron transfer to a host material whose energy levels are suffi ciently low for avoiding further charge transfer to oxygen-water complexes. Our results show the feasibility of temporarily handling n-doped organic thin fi lms in air, e.g., during structuring of organic fi eld effect transistors (OFETs) by lithography.