Transparent conductive oxides (TCOs) are employed as contact layers thin film solar cells. They transmit incoming light to the absorber and conduct the generated charge carriers laterally to the metal contacts. Thus, the TCO should have a high optical transparency as well as a high electrical conductivity to ensure good solar cell performance. The free charge carriers, which are necessary for the electrical conductivity, also cause free carrier absorption in the near infrared (NIR) spectrum. In order to fulfill the two conflicting requirements mentioned above, it is necessary to reduce the free carrier density and increase the carrier mobility in the TCO at the same time. By accomplishing this, high optical transparency can be achieved while still maintaining a good electrical conductivity. Increasing the transparency of the TCO increases the short-circuit current density (Jsc) in solar cells. [1] On a-Si:H/µc-Si:H thin film solar cells the back-contact and reflector typically consist of a thin ZnO:Al (AZO) buffer layer and a silver layer. The high cost of silver as well as plasmonic absorption make it desirable to use a silver-free backside reflector. We report that a backside contact composed of an AZO transparent conducting oxide (TCO) layer deposited by DC-magnetron-sputtering at 180 °C combined with a white paint backside reflector can achieve almost the same solar cell performance as a TCO/silver back contact. [2] Hydrogen doped indium oxide In2O3:H (IOH) has been widely discussed as a suitable contact layer for thin film solar cells , because of its mobility higher than 100 cm2 / Vs [3]. Very low optical absorption can be achieved with this material at resistivities around 350 µΩcm. In this work, a deposition and annealing process for IOH has been developed and optimized. It could be demonstrated that the short circuit current density of a-Si:H/c-Si heterojunction cells as well as CIGS-cells with IOH front contacts could be improved compared to cells with standard ITO- and AZO front contacts. [4] In IOH films deposited statically by rf magnetron sputtering, a small area directly opposing the target center with a higher resistivity and lower crystallinity than the rest of the film has been found via hall- and XRD-measurements, which we attribute to plasma damage. In order to investigate the distribution of particle energies during the sputtering process we have simulated the RF-sputtering deposition process of IOH by Particle-In-Cell Monte-Carlo simulation. At the surface of ceramic sputtering targets, negatively charged oxygen ions are created. These ions are accelerated towards the substrate in the plasma sheath with energies up to 150 eV. Particle energies in this order of magnitude damage the growing film, reduce crystallinity and should be avoided in order to achieve good material properties. The influence of a negatively biased mesh inside the sputtering chamber on particle energies and distributions has been simulated and investigated. We found that the mesh decreased the high energetic oxygen ion density at the substrate, thus enabling a more homogeneous IOH film growth. The theoretical results have been verified by XRD, 4-point-probe and hall measurements of statically deposited IOH films on glass. [5] [1] H. Scherg-Kurmes, S. Seeger, S. Körner, R. Schlatmann, B. Rech, und B. Szyszka, „Optimization of the post-deposition annealing process of high mobility In2O3:H for photovoltaic applications“, Thin Solid Films, Bd. 599, S. 78–83, 2016. [2] H. Scherg-Kurmes u. a., „Comparative study of backside reflectors on a-Si:H/µc-Si:H thin film solar cells“, Phys. Status Solidi A, Bd. 211, S. 2078–81, 2014. [3] T. Koida, H. Fujiwara, und M. Kondo, „Hydrogen-doped In2O3 as High-mobility Transparent Conductive Oxide“, Jpn. J. Appl. Phys., Bd. 46, Nr. 28, S. L685–L687, 2007. [4] H. Scherg-Kurmes u. a., „High mobility In2O3:H as contact layer for a-Si:H/c-Si heterojunction and mc-Si:H thin film solar cells“, Thin Solid Films, Nr. 0, S. , 2015. [5] H. Scherg-Kurmes u. a., „Improvement of the homogeneity of high mobility In2O3:H films by sputtering through a mesh electrode studied by Monte Carlo simulation and thin film analysis“, Phys. Status Solidi A, Bd. 213, Nr. 9, S. 2310–2316, 2016.


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    Title :

    Deposition von transparenten leitfähigen Oxiden mit hoher Ladungsträgermobilität bei niedriger Prozesstemperatur und deren Integration in Photovoltaik-Zellen.
    numerical simulation of the chemical and physical phenomena during the deposition process


    Subtitle :

    numerische Simulation der physikalischen und chemischen Vorgänge während der Deposition


    Additional title:

    Deposition of high mobility transparent conductive oxides and their integration into solar cells


    Contributors:

    Publication date :

    2017



    Type of media :

    Miscellaneous


    Type of material :

    Electronic Resource


    Language :

    German



    Classification :

    DDC:    629




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