Reverse bias activation of salt-doped polymer light-emitting devices

We report sandwich polymer light-emitting devices doped with a lithium salt. The salt-doped polymer devices are initially conductive and weakly emitting under forward bias but blocking under reverse bias. The application of a large reverse bias or current activates the device, causing a dramatic increase in current and the onset of electroluminescence under reverse bias. Meanwhile, the forward-bias current and emission have become heavily suppressed. Moreover, the activated devices exhibit photovoltaic response whose polarity is opposite to that of an un-activated device. Electrical, electroluminescent, photoluminescent and photovoltaic properties of the activated devices suggest the formation of a p–n junction by in situ electrochemical doping. Devices made with a green-emitting polymer are quasi-frozen with no significant degradation in current density and light intensity after 1200 h of storage at room temperature.