Electrodes for GaOHPc:PCBM/P3HT:PCBM bulk heterojunction solar cell

The bulk heterojunction approach appears to be one of the most promising concepts of creating efficient, low cost and easily producible organic solar cells. For this purpose one of the best materials was regioregular poly-3-hexylthiophene (P3HT), which is widely used as a donor molecule and a hole transporter, with soluble fullerene derivative (PCBM) as an acceptor and electron transporter. The main drawback of this highly efficient blend is its limited spectral range, covering only a 350-650 nm spectral interval. So the main aim of the present work was to extend the spectral range of the cell up to 850 nm by adding a second bulk heterojunction layer of complementary absorption spectrum to the P3HT: PCBM layer. Therefore hydroxygallium phthalocyanine (GaOHPc) and PCBM blend was used as an additional layer because GaOHPc has strong and wide intermolecular charge transfer (CT) absorption band of around 830-850 nm. Thus an organic bi-layer bulk heterojunction system GaOHPc:PCBM/P3HT:PCBM has been built by the spin coating technique having high charge carrier photogeneration efficiency in the 350-850 nm spectral range. The cell annealing temperature influence on the cell performance has been investigated in a 10(-6) mbar vacuum within the temperature range from 30 degrees C to 100 degrees C. It was found that annealing at 100 degrees C increases the short-circuit photocurrent external quantum efficiency (EQE) values more than 2 times. Various top electrodes of Al, In and Yb/Al/Se were examined to achieve the best performance of our bi-layer cell. It was found that the best power conversion efficiency (PCE) is provided by an Yb/Al electrode covered with a protective Se layer. (C) 2012 Elsevier B.V. All rights reserved.