Ortsaufgelöste Charakterisierung organischer Solarzellen mittels Lumineszenzstrahlung

Stipendiatin/Stipendiat: Dr. Marco Seeland

Solarzellen auf der Basis konjugierter Polymere sind aussichtsreiche Vertreter der Dünnschichtphotovoltaik. Im Labormaßstab werden mittlerweile Energiekonversions-effizienzen erreicht, die mit denen kommerzieller Dünnschichttechnologien, z.B. amorphen Silizium-solarzellen, vergleichbar sind [1]. Aufgrund der potentiell niedrigen Material- und Prozessierungskosten und einem gleichzeitig hohen Produktionsdurchsatz wächst die umweltpolitische wie kommerzielle Relevanz dieser Technologie stetig [2]. Die Verwendung organischer Materialien birgt jedoch den Nachteil einer geringen Stabilität gegenüber Umwelteinflüssen. Das komplexe Zusammenwirken von physikalischen und chemischen Prozessen im Schichtaufbau der Solarzelle führt zu einer vergleichbar schnellen Degradation, d.h. einer zeitlich fortschreitenden Verringerung der Effizienz [3]. Darüber hinaus wirkt sich die generelle Architektur von Dünnschichtsolarzellen negativ auf die Effizienz hochskalierter Solarzellen mit großer Fläche aus [4].

 

Im Rahmen dieses Promotionsprojektes wird eine Messmethodik zusammen mit einer entsprechenden Modellierung entwickelt, die die schnelle und gezielte Charakterisierung von Dünnschichtsolarzellen ermöglichen. Exemplarisch werden dabei in erster Linie Polymer-Solarzellen und -Module untersucht. Das Messverfahren, welches auf der ortsaufgelösten Detektion von Lumineszenzstrahlung mittels CCD-Kamera basiert, ist dabei einfach umsetzbar und kann nach hinreichender Optimierung zukünftig eine erweiterte Charakterisierung während des Produktionsprozesses ermöglichen. Neben den technischen Aspekten der Methodik sowie deren Einsatz zur Qualitätskontrolle von Solarzellen spielen insbesondere die physikalischen Aspekte des detektierten Messsignals eine wesentliche Rolle. Durch kombinierte elektrische und optische Anregung des photoaktiven organischen Materials wird mit der entwickelten Methode erstmals eine qualitative und quantitative Unterscheidung zwischen Degradation der Ladungsträger-injizierenden Elektroden und des Licht absorbierenden bzw. emittierenden organischen Halbleiters erreicht [5, 6]. Für eine quantitative Analyse zur Bestimmung von Materialeigenschaften lassen sich Rezipozitätsrelationen ableiten, die aus der physikalischen Umkehrbarkeit mikroskopischer Prozesse resultieren [7, 8]. Für eine, aufgrund der Dünnschichtarchitektur benötigte, laterale Modellierung werden die abgeleiteten Relationen mit einem Modell verknüpft, das die lokale Beschreibung der Solarzelle erlaubt [9]. Die kombinierte Modellierung wird dann im Rahmen von Simulationen genutzt, um reale lokale Defekte theoretisch zu reproduzieren und um deren Einfluss auf das globale Leistungsverhalten der Solarzelle zu bestimmen.

 


[1] M. A. Green, K. Emery, Y. Hishikawa, et al., Progress in Photovoltaics: Research and Applications 20, 606-614 (2012).
[2] T. D. Nielsen, C. Cruickshank, S. Foged, et al., Sol. Energy Mater. Sol. Cells 94, 1553-1571 (2010).
[3] M. Jørgensen, K. Norrman and F. C. Krebs, Sol. Energy Mater. Sol. Cells 92, 686-714 (2008).
[4] H. Hoppe, M. Seeland and B. Muhsin, Solar Energy Materials and Solar Cells 97, 119-126 (2012).
[5] M. Seeland, R. Rösch and H. Hoppe, Journal of Applied Physics 109, 064513 (2011).
[6] M. Seeland, R. Rösch and H. Hoppe, Imaging Techniques for Studying OPV Stability and Degradation, in Stability and Degradation of Organic and Polymer Solar Cells, edited by F. C. Krebs (John Wiley & Sons, 2012).
[7] P. Würfel, Journal of Physics C-Solid State Physics 15, 3967-3985 (1982).
[8] U. Rau, Physical Review B 76, 085303 (2007).
[9] M. Seeland, R. Rösch and H. Hoppe, Journal of Applied Physics 111, 024505 (2012).

Förderzeitraum:
01.11.2011 - 31.10.2014

Institut:
Technische Universität Ilmenau
Institut für Physik
FG Experimentalphysik I

Betreuer:
Prof. Dr. Gerhard Gobsch

E-Mail: E-Mail schreiben

URL: http://www.tu-ilmenau.de/secsy/

Publikationen:

  • Stability of polymer solar cells: Dependence on working pressure
    We investigated the degradation behavior of polymer/fullerene solar cells processed at different working pressures during the deposition of the metal back electrode by physical vapor deposition (PVD). The temporal development of the photovoltaic parameters was determined with a homemade automated degradation setup for constant irradiation of similar to 1000 W/m(2) in air. The initial device efficiency improved with evacuation time. The device stability itself depended also on the PVD working pr
  • Optimal geometric design of monolithic thin-film solar modules: Architecture of polymer solar cells
    In this study the geometrical optimization of monolithically integrated solar cells into serially connected solar modules is reported. Based on the experimental determination of electrodes' sheet and intermittent contact resistances, the overall series resistance of individual solar cells and interconnected solar modules is calculated. Taking a constant photocurrent generation density into account, the total Joule respectively resistive power losses are determined by a self-consistent simul
  • Quantitative evaluation of inhomogeneous device operation in thin film solar cells by luminescence imaging
    We present a method for quantitative evaluation of electroluminescence images from thin film solar cells. The method called “quantitative electroluminescence imaging” (QuELI) is based on decoupling local equivalent circuit parameters and allows calculation of the local current-density as well as the local series resistance and saturation current-density. By application of this method to electroluminescence images obtained from polymer-fullerene based solar cells, we show that QuELI allows effici
  • Quantitative analysis of electroluminescence images from polymer solar cells
    We introduce the micro-diode-model (MDM) based on a discrete network of interconnected diodes, which allows for quantitative description of lateral electroluminescence emission images obtained from organic bulk heterojunction solar cells. Besides the distributed solar cell description, the equivalent circuit, respectively, network model considers interface and bulk resistances as well as the sheet resistance of the semitransparent electrode. The application of this model allows direct calculatio
  • Luminescence imaging of polymer solar cells: Visualization of progressing degradation
    We apply luminescence imaging as tool for the nondestructive visualization of degradation processes within bulk heterojunction polymer solar cells. The imaging technique is based on luminescence detection with a highly sensitive silicon charge-coupled-device camera and is able to visualize with time advancing degradation patterns of polymer solar cells. The devices investigated have been aged under defined conditions and were characterized periodically with current-voltage (I-V) sweeps. This all
  • Locally resolved large scale phase separation in polymer:fullerene blends
    We report a comprehensive study probing the influence of polymer blending on the large scale phase separation by the use of electroluminescence imaging (ELI) and light-beam induced current (LBIC) measurements. The study is based on a semi-crystalline and an amorphous analogue of anthracene-containing poly(p-phenylene-ethynylene)-alt-poly(p-phenylene-vinylene) (PPE–PPV) copolymer (AnE-PVs) blended with [6,6]-phenyl-C61-butyric acid methyl ester (PCBM). Since the semi-crystalline polymer AnE-PVab
  • Investigation of the degradation mechanisms of a variety of organic photovoltaic devices by combination of imaging techniques-the ISOS-3 inter-laboratory collaboration
    The investigation of degradation of seven distinct sets (with a number of individual cells of n >= 12) of state of the art organic photovoltaic devices prepared by leading research laboratories with a combination of imaging methods is reported. All devices have been shipped to and degraded at Riso DTU up to 1830 hours in accordance with established ISOS-3 protocols under defined illumination conditions. Imaging of device function at different stages of degradation was performed by laser-beam ind
  • Water ingress into and climate dependent lifetime of organic photovoltaic cells investigated by calcium corrosion tests
    The degradation of non-encapsulated, small-molecule organic solar cells based on ZnPc (zinc phthalocyanine)/C-60 with an aluminum top electrode is investigated under different climate conditions and correlated with the water barrier performance of the aluminum electrode layer. The degradation of the solar cells turns out to be dominated by water and can be well predicted by the corrosion of calcium - a sensor for water - under the same conditions. By several independent techniques, an amount of
  • An inter-laboratory stability study of roll-to-roll coated flexible polymer solar modules
    A large number of flexible polymer solar modules comprising 16 serially connected individual cells was prepared at the experimental workshop at Riso DTU. The photoactive layer was prepared from several varieties of P3HT (Merck, Plextronics, BASF and Riso DTU) and two varieties of ZnO (nanoparticulate, thin film) were employed as electron transport layers. The devices were all tested at Riso DTU and the functional devices were subjected to an inter-laboratory study involving the performance and t
  • Comparison of distributed vs. lumped series resistance modeling of thin-film solar cells and modules: Influence on the geometry-dependent efficiency
    Limited lateral conductivities of the photo-active materials used in thin-film solar cells necessitate the use of semitransparent electrodes for current collection and lateral current transport. Due to the tradeoff between electrical conductivity and optical transmission, which should not underrun 80%, typical values for the sheet resistances of semitransparent electrodes deposited on glass amount to 10–20 Ω/sq. The power loss due to Joule heating and the accompanying voltage drop caused by this
  • Imaging Techniques for Studying OPV Stability and Degradation
    Bookchapter
Laterale elektrooptische Charakterisierung von organischen Solarzellen
Laterale elektrooptische Charakterisierung von organischen Solarzellen