Dominik Daume

Sample preparation for scanning Kelvin probe microscopy studies on cross sections of organic solar cells

We prepared cross sections of P3HT:PCBM bulk heterojunction (BHJ) organic solar cells (OSCs) for the characterization of their potential distribution with scanning Kelvin probe microscopy. We compared results of samples obtained by microtome cutting of OSCs on plastic substrates, cleaving of OSCs on glass substrates, and milling with a focused ion beam. Their potential distributions were in good agreement with each other. Under short circuit conditions, potential gradients were detected in vicinity of the electrode/organics interfaces, with negligible electric fields within the bulk. We contacted the OSCs in a defined manner and studied their potential distribution under operating conditions.

Poly(para-phenyleneethynylene)s as Emitters in Polymer LEDs

11 different dialkoxy- and dialkyl-poly(para-phenyleneethynylene)s (PPEs) featuring novel branched and literature described linear and branched side chains were prepared using a Sonogashira coupling. The side chains were of different length and branching character. The degree of polymerization of the PPEs ranged from Pn = 44–343 with polydispersities ranging from 1.5–3.1. Fairly simple OLED-stacks with up to three layers (electron injection, emitter layer, and hole injection) were produced. Depending upon the PPEs’ structure and the stack architecture but particularly the thickness of the emitting PPE-layer, a large increase in brightness up to 2.2 × 103 cd m−2 was observed, a significant improvement over earlier reported values.