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Plasma-enhanced atomic layer deposited (PEALD) aluminum oxide (Al2O3) thin film were investigated with respect to their application in silicon solar cells where not only excellent surface passivation but also excellent electrical insulation properties are required. In this study, the insulation properties of about 10 nm to almost 250 nm Al2O3 thin films, deposited at temperatures in the range of 100 °C to 350 °C and annealed in the range of 250 °C to 450 °C, were correlated to various thin film properties, most notably the thin film defect density, i. e. pinhole density, and the thin film stress. Al2O3 thin films provide sufficient electrical insulation after a post-deposition annealing step at 450 °C when deposited at 250 °C with thickness of at least 80 nm which can be attributed to a low defect density and low stress in the thin films, allowing a low leakage current density and a high breakdown voltage that was independent of the type of metals used for the electrode. Al2O3 thin films deposited and annealed at these temperatures enabled a very good surface passivation of silicon. These results indicate that Al2O3 thin films realized by PEALD are a promising candidate for silicon solar cells that rely on passivating as well as insulating thin films.

A heterostructure of zinc oxide (ZnO) and single layer graphene is fabricated by sandwiching a transferred graphene between two thin ZnO films (∼20 nm each). ZnO thin films were grown using decomposition of Zn(acac)2 and spin-coating technique. Graphene transfer route with PMMA temporary carrier and metal etching process was used to transfer high quality commercial graphene from copper foil on the zinc oxide surface on glass. This novel and ultra-thin heterostructure (∼40 nm) is sensitive for UV illumination and works as a photodetector (PD). In this device, both positive and negative photoconductivity (PC) were observed depends on illumination intensity and spectrum of incident light. Relatively long response and recovery times obtained in ZnO/G/ZnO structure are related to the metastable defect states of ZnO and its interfaces with graphene and/or silver contacts. The obtained results show that the transferred single layer graphene sheet between thin ZnO films could be a novel route for improvement properties this low-cost metal oxide.

This paper is devoted to the development of standard and inverted polymer solar cells based on polyazomethine (PAZ-Car-TPA), poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl C 61 butyric acid methyl ester (PCBM). We analyzed the influence of: (i) PEDOT:PSS or MoO 3 as a hole transporting layer in standard devices, (ii) aluminum doping level (from 0 to 3.7%) in ZnO (obtained by atomic layer deposition, ALD) applied as an electron transporting layer in inverted solar cells and (iii) the method applied to obtain ZnO layer (ALD or sol-gel) on its photovoltaic properties. The best device configuration is ITO/AZO (3% Al)/P3HT:PCBM/MoO 3 /Ag which exhibits a power conversion efficiency of 1.51% under about 100 mW/cm 2 AM 1.5 G simulated solar emission. Devices were additionally tested by electrochemical impedance spectroscopy. HOMO-LUMO levels of PAZ-Car-TPA and its mixture with HCl, H 2 SO 4 , p-toluenesulfonic acid, PEDOT:PSS and water were analyzed by cyclic voltammetry and quantum mechanical calculations using Density Functional Theory method.

Flexible films with high barrier properties against water and oxygen are currently in the focus for applications in an increasing number of technical fields, e.g. electronic and optical devices. In this research work, high performance functional coatings, based on hybrid organic/inorganic materials, are being developed to combine the polymer flexibility and ease of processing with the rigidity and thermal stability of inorganic materials. The main goal was to obtain low-cost and low-temperature barrier layer for flexible solar cells with high transparency and hydrophobic properties. Surface morphology and surface performance together with hydrophobic and optical properties were examined and compared for various samples. Moreover, some preliminary permeability tests were carried out for selected samples to indicate for some improvement in terms of barrier quality.

All-screen-printed back-contact back-junction silicon solar cells with aluminum-alloyed emitter on n-type base material were fabricated and analyzed at Fraunhofer ISE PV-TEC. Three different process sequences are compared to each other. One process flow with shallow phosphorus profiles realizes cells with efficiencies of 19.7%. Using a long thermal oxidation, cells with deep driven-in phosphorus profiles (front and back surface field) were processed where solar cell efficiencies of 20.0% are realized. Both cell efficiencies are independently measured at Fraunhofer ISE CalLab on a designated area of 16.65 cm2. The specific contact resistivity of screen-printed and fired silver paste to silicon surfaces with different phosphorus profiles was determined in dependence of several firing conditions. The main developed features of the presented cell structure comprise the firing-stable front and rear passivation layers, the spiking-free passivation layer against aluminum and the deep driven-in phosphorus profile that can be contacted by silver screen-printing paste in a firing step.

The performance of n-type Si back-contact back-junction (BC-BJ) solar cells under illumination with high energy ultraviolet (UV) photons was investigated. The impact of the phosphorus doped front surface field (FSF) layer on the stability of the front surface passivation under UV illumination was investigated. Lifetime samples and solar cells without the front surface field showed a significant performance reduction when exposed to ultraviolet light. The surface saturation current density ( J 0e ) increased from 48 to 446 fA/cm 2 after the UV exposure. At the same time the efficiency of the BC-BJ solar cells without the FSF diffusion reduced from 19.8% to 14.3%. In contrast to the lifetime samples and solar cells without the FSF diffusion, the tested n + nn + structures and the BC-BJ solar cells with applied FSF diffusion profiles were significantly more stable under UV exposure, i.e. J 0e increased only by a factor of 25% and the efficiency of these cells decreased only 0.3% abs by the UV illumination. Finally it was shown that the performance of the UV-degraded solar cells without FSF could be improved during a forming gas anneal (FGA). Due to application of FGA the efficiency almost fully recovered from 14.3% to 19.6%.