Reduced amplified spontaneous emission threshold in organic semiconductor laser structure with relaxed roll-off characteristics under high current densities

We reduced the amplified spontaneous emission (ASE) threshold in an organic semiconductor laser structure by the introduction of an exciton blocking layer adjacent to the cathode layer. A phenyl-dipyrenylphosphine oxide (POPy ₂) layer with the function of an electron transport layer and the exciton blocking layer were inserted between an active layer of 4,4-bis[N-(carbazole)styrylbiphenyl] (BSB-Cz) and a metal cathode layer. The electron injection barrier from POPy₂ to BSB-Cz is downward, indicating no net energy barrier, and the hole injection barrier from the BSB-Cz layer into the POPy₂ layer is also small because of the similarity between the highest occupied molecular orbital levels of the materials. Therefore, the proposed device structure can avoid extra carrier accumulations at the heterointerface, leading to compatibility in terms of both relaxation of the exciton-polaron annihilation and blocking of the energy transfer from the BSB-Cz layer into the cathode layer.