Enhanced performance of SubPc planar heterojunction solar cells with a novel luminescent sensitizer of 4,4′-bis[(N-carbaz ole)styryl]biphenyl

Abstract

Here, the conventional luminescent material 4,4′-bis[(N-carbazole) styryl] biphenyl (BSB-Cz) is used as luminescent sensitizer in boron subphthalocyanine chloride (SubPc)/C60 planar heterojunction (PHJ) solar cells for the first time. When inserting 3-nm BSB-Cz between the MoO3 and donor layer, the power conversion efficiency (PCE) of SubPc/C60 PHJ is improved from 1.21% to 1.72%. BSB-Cz at 3–8nm all enhances the short-circuit current (JSC) and open-circuit voltage. As BSB-Cz is capable of absorbing short-wavelength solar light and re-emitting long-wavelength light which is exactly located at the absorption wavelength range of SubPc and C60. The JSC increase is attributed to the electron-blocking effect of BSB-Cz together with matched photoluminescence spectrum of BSB-Cz and the absorption spectra of SubPc as well as C60, which enhances the incident photon number for SubPc and C60. AFM images indicate that the bumpy surface of 3-nm BSB-Cz is filled in by the subsequent SubPc layer, thus decreases the surface roughness. However, thicker BSB-Cz results in significantly increased RMS roughness with decreased fill factor. The thickness of BSB-Cz maybe decides the only donor or two competing donors at the donor/acceptor interface, which affects the exciton disociattion and recombination in the overall device.