Performance improvement of DBP-based solar cells by introducing a luminescent sensitizer bis[(4,6-difluorophenyl)-pyridinato-N,C^2′]c(picolinate)iridium(III) (FIrpic)

Abstract

In this work, a sky-blue luminescent down-shifting (LDS) layer bis[(4,6-difluorophenyl)-pyridinato-N,C^2′]c(picolinate)iridium(III) (FIrpic) was inserted between tetraphenyldibenzoperiflanthene (DBP) and MoO₃ as UV-screen and sensitizer for small molecule DBP/C₆₀ based planar heterojunction (PHJ) solar cells. With 8-nm FIrpic the short circuit current (J_sc) and power conversion efficiency (PCE) of the device are enhanced by 28% and 15%, respectively, probably originating from the re-absorption of the photons emitted from FIrpic. The V_oc linearly increases over 1-nm FIrpic, ascribed to the deeper HOMO level of FIrpic than DBP, while the fill factor continuously declines from 3- to 10-nm FIrpic. The EQE spectra prove that the J_sc is mainly contributed by the photocurrent generated in DBP and C₆₀ layers. When the FIrpic thickness is 8 nm, the film surface is very uniform with the smallest water contact angle. The impedance spectroscopy demonstrates that the device resistance gradually increases from 4.1×10⁴ W (without FIrpic) to 4.6×10⁴ W (with 10-nm FIrpic) with the FIrpic thickness rise, simultaneously the device transits from the insulating state into the conductive state faster for the thin FIrpic layer than the thick layer.

Keywords

small molecule solar cell / sky-blue luminescent sensitizer / UV-screen / FIrpic / DBP

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