Improved electron collection in fullerene via caesium iodide or carbonate by means of annealing in inverted organic solar cells

¹ L’UNAM, Université de Nantes, MOLTECH-Anjou, CNRS, UMR 6200, 2 rue de la Houssinière, BP 92208, 44000 Nantes, France
² Laboratoire Optoélectronique et Physico-chimie des Matériaux, Université Ibn Tofail, Faculté des Sciences, BP 133, 14000 Kenitra, Morocco
³ Université de Nantes, Institut des Matériaux Jean Rouxel (IMN), CNRS, UMR 6502, 2 rue de la Houssinière, BP 32229, 44322 Nantes Cedex 3, France
⁴ Laboratory for Unconventional Electronics and Photonics, Department of Physics, National Institute of Technology, 673 601 Calicut, Kerala, India
⁵ L’UNAM, Université de Nantes, Faculté des Sciences et des Techniques, 2 rue de la Houssinière, BP 92208, 44000 Nantes, France

^a e-mail: jean-christian.bernede@univ-nantes.fr

Received: 27 November 2013
Accepted: 16 January 2014
Published online: 6 May 2014

Abstract

Inverted organic photovoltaic cells (IOPVCs), based on the planar heterojunction C₆₀/CuPc, were grown using MoO₃ as anode buffer layer and CsI or Cs₂CO₃ as cathode buffer layer (CBL), the cathode being an ITO coated glass. Work functions, Φ_f, of treated cathode were estimated using the cyclic voltammetry method. It is shown that Φ_f of ITO covered with a Cs compounds is decreased. This decrease is amplified by the annealing. It is shown that the thermal deposition under vacuum of the CBL induces a partial decomposition of the caesium compounds. In parallel, the formation of a compound with the In of ITO is put in evidence. This reaction is amplified by annealing, which allows obtaining IOPVCs with improved efficiency. The optimum annealing conditions is 150 °C for 5 min.