Transient current-transient voltage [i(t)-v(t)], transient brightness-transient current [b(t)-i(t)], and transient brightness-transient voltage [b(t)-v(t)] analysis are introduced as novel organic light emitting device (OLED) characterization methods. These analysis methods involve measurement of the instantaneous voltage [v(t)] across, the instantaneous current [i(t)] through, and the instantaneous brightness [b(t)] from an OLED when it is subjected to a bipolar, piecewise-linear applied voltage waveform. Employing these characterization methods, two important OLED device physics conclusions are obtained: (1) Hole accumulation at the electron transport layer (ETL)/hole transport layer (HTL) interface plays an important role in establishing balanced charge injection of electrons and holes into the OLED. (2) Hole accumulation at the ETL/HTL interface is more important in establishing the ac conduction characteristics than charge trapping in the ETL.