The effect of charge imbalance and accumulation on the stability of the hole transporting layer PEDOT: PSS in devices is studied during device operation. The principal Raman peak of PEDOT at around 1420-1430 cm (1) is weakened and undergoes band broadening cum shift due to oxidation by holes injected from the ITO anode (doping). Upon suspending the applied potential, the oxidized PEDOT converts back to its as-prepared state. The oxidation of PEDOT is found to be reversible as long as the applied potential is kept relatively low as higher potential would induce PEDOT decomposition. (C) 2014 Elsevier B.V. All rights reserved.