Irradiation-induced molecular dipole reorientation in inverted polymer solar cell using small molecular electron collection layer

Inverted polymer solar cell is developed using small molecular tris(8-hydroxyquinolinato) aluminum (Alq₃) as an electron collection layer between the active layer and indium-tin-oxide bottom cathode. Upon post-processing light irradiation by simulated solar illumination, the open-circuit voltage of the inverted device increases from 0.52 V to 0.60 V, resulting in the enhancement of the power conversion efficiency from 2.54 to 3.33 with negligible change in the short-circuit current. The performance improvement is attributed to the removal of surface potential due to irradiation-induced molecular dipole reorientation in the Alq₃ layer, which reduces the charge transport barrier and improves the charge collection efficiency.