Effect of molecular weight on the efficiency of poly(N-vinylcarbazole)-based polymer light-emitting diodes

Polymer light-emitting diodes based on poly(N-vinylcarbazole) (PVK) with molecular weights M-W of 1.1 x 10(6) and similar to 7.5 x 10(4) are compared. For devices without an electron transport layer (ETL), the high M-W PVK yields higher external quantum efficiency (0.67% vs 0.18%), but for devices with an ETL, the low MW PVK yields higher efficiency (1.13% vs 0.83%). This intriguing difference is believed to result from higher energetic disorder in the high M-W polymer and different recombination zone-quenching metal electrode distances, in agreement with Konezny et al. [Appl. Phys. Lett. 97, 143305 (2010)]. (C) 2011 American Institute of Physics. [doi:10.1063/1.3659467]