Organic solar cells (OSCs) based on polymers and small molecules have seen a tremendous increase in interest during the past few years. Signifi cant progress in this fi eld seeded the prospect for a cost-effective and easy-to-fabricate photovoltaic technology-typical advantages claimed for organic (opto-)electronic devices. Very recently, certifi ed cell effi ciencies in excess of 7% have been reported for polymer based cells. [ 1 ] For large-scale and high-throughput production of OSCs, liquid processing of the functional layers is desirable. Aside from the active organic layers, inter-layers are typically required to facilitate the extraction of the photo-generated charges. Specifi cally, on the anode side, polyethylene dioxythiophene:polystyrenesulfonate (PEDOT:PSS) is regularly used. [ 2 ] However, PEDOT:PSS is burdened with structural and electrical inhomogeneity [ 3,4 ] and has been demonstrated to be an origin of limited device lifetime. [ 5 ] Particularly, the aqueous PEDOT:PSS dispersion and the acidic nature can cause substantial degradation. [6,7 ] Very recently, transition metal-oxides (TMOs) such as molybdenum-, vanadium-, or tungsten-oxide (MoO 3 , V 2 O 5 , and WO 3 ) with high work functions (WFs) of up to 6.9 eV have been shown to be promising alternatives to PEDOT:PSS. [8][9][10][11] TMOs have also been used as constituents of the connecting architecture in stacked organic light-emitting diodes and organic tandem solar cells. [12][13][14][15] The unique energetics of these TMOs has so far been predominantly accessible for fi lms thermally evaporated in high-vacuum.The fi rst results for TMO layers obtained by solution processing from nano-particle (NP) dispersions have been reported only very recently. [ 16,17 ] Meyer et al. prepared MoO 3 layers by dispersing MoO 3 NPs using a polymer as dispersing agent. After deposition, the layers had to be treated by an oxygen plasma to remove the polymer. A high WF of the resulting layers of 5.7-6 eV was obtained. A substantial drawback of the approach, however, is the observation of larger NP aggregates with a size of 100 nm and an overall high roughness of 25 nm (rms). Owing to their roughness these NP-layers are critical sources of shorts, especially over a large device area.In contrast, TMO layers (WO 3 , V 2 O 5 and MoO 3 ) have been prepared by sol-gel deposition, predominantly for electrochromic, catalytic and sensing applications. [18][19][20][21] Post processing of the sol-gel TMO layers at high temperatures (300 ° C-600 ° C) is routinely applied in order to achieve specifi c microstructures or crystalline phases in the materials, as required by the particular application. These high processing temperatures are not compatible with the temperature-sensitive substrates (e.g. poly mer foils) envisaged for low-cost, high-throughput fabrication of organic solar cells. In spite of this limitation, Steirer et al. have very recently used NiO prepared via a sol-gel route as a replacement for PEDOT:PSS in an organic solar cell. [ 22 ] The requirement of pos...

To increase efficiency of bulk heterojunctions for photovoltaic devices, the functional morphology of active layers has to be understood, requiring visualization and discrimination of materials with very similar characteristics. Here we combine high-resolution spectroscopic imaging using an analytical transmission electron microscope with nonlinear multivariate statistical analysis for classification of multispectral image data. We obtain a visual representation showing homogeneous phases of donor and acceptor, connected by a third composite phase, depending in its extent on the way the heterojunction is fabricated. For the first time we can correlate variations in nanoscale morphology determined by material contrast with measured solar cell efficiency. In particular we visualize a homogeneously blended phase, previously discussed to diminish charge separation in solar cell devices.

We reported on highly efficient semitransparent polymer solar cells comprising a transparent sputtered indium tin oxide (ITO) top electrode. We used an inverted cell structure with titanium dioxide prepared by atomic layer deposition as electron selective layer and molybdenum oxide (MoO3) as hole extraction layer. Moreover, the MoO3 layer prevents damage to the organic active materials due to the ITO sputtering process. For the semitransparent device, power conversion efficiencies of 1.9% were achieved with a high transmittance of 80% in the red region of the visible spectrum.

Organic bulk heterojunction solar cells using titania interlayers as electron selective layers prepared by atomic layer deposition or wet processing are reported. Pristine devices show low filling factors (FFs) and consequently low efficiencies. Upon illumination with ultraviolet (UV) light, a significant increase in the FF is found. We study the impact of various ambient conditions (air, vacuum, and oxygen) on the dynamics of the decay of the FF after UV illumination. The interaction of oxygen and titania is evidenced as the dominant mechanism for the transient behavior of the polymer solar cells.

This paper reports on thin film gas-diffusion barriers consisting of Al2O3/ZrO2 nanolaminates (NL) grown by low-temperature (80 °C) atomic layer deposition. We show that reliable barriers with water vapor transmission rates of 3.2×10−4 g/(m2 day), measured at 80 °C and 80% relative humidity, can be realized with very thin layers down to 40 nm. We determine that ZrO2 acts as anticorrosion element in our NL. Furthermore, we demonstrate by x-ray photoemission spectroscopy that an aluminate phase is formed at the interfaces between Al2O3 and ZrO2 sublayers, which additionally improves the gas-diffusion barrier due to a densification of the layer system. These Al2O3/ZrO2 NLs prepared at low temperatures hold considerable promises for application in organic electronics and beyond.