Effect of concentration gradients in ZnPc:C₆₀ bulk heterojunction organic solar cells

Journal article

A concentration gradient in a mixed absorber layer with increasing content of donor (acceptor) towards the hole (electron) collecting contact could improve the charge carrier collection in bulk heterojunction organic solar cells. We study p-i-metal type solar cells where the gradient in a 45 nm thick ZnPc:C₆₀ absorber layer is introduced by varying the deposition rate during co-evaporation. It is shown that the observed increase in the performance is mainly caused by a better energy level alignment and reduced recombination at the p-side. A significant influence on charge carrier transport is not observed. However, regions with a concentration of less than 20% of one component do not fully contribute to the photocurrent. Voltage dependent external quantum efficiency data are used to identify the photoactive regions. © 2011 Elsevier B.V. All rights reserved.

Authors: Tress, W; Leo, K; Riede, M

• Publication status: Published
• Peer review status: Peer reviewed
• Publisher: Elsevier
• Journal: Solar Energy Materials and Solar Cells
• Volume: 95
• Issue: 11
• Pages: 2981-2986
• Publication date: 2011-11-01
• DOI: 10.1016/j.solmat.2011.06.003
• ISSN: 0927-0248
• Language: English
• Keywords: Drift-diffusion model; External quantum efficiency; Open-circuit voltage; Small molecule; Graded heterojunction; Interface recombination