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

doi:10.1007/s11706-021-0533-0

Front. Mater. Sci.

2021, Vol. 15

Issue (1) : 158-165 https://doi.org/10.1007/s11706-021-0533-0

RESEARCH ARTICLE

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)

Jie TANG^1,², Weiguang LI^1,², Juncong CHEN^1,², Yanqiong ZHENG¹(

), Junbiao PENG³(

), Jianhua ZHANG¹, Bin WEI¹, Xifeng LI¹

¹. Key Laboratory of Advanced Display and System Applications (MOE), School of Mechatronic Engineering and Automation, Shanghai University, Shanghai 200072, China
². School of Materials Science and Engineering, Shanghai University, Shanghai 200072, China
³. State Key Laboratory of Luminescent Materials and Devices, South China University of Technology, Guangzhou 510640, China

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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

Corresponding Author(s): Yanqiong ZHENG,Junbiao PENG

Online First Date: 05 February 2021 Issue Date: 11 March 2021

Cite this article:

Jie TANG,Weiguang LI,Juncong CHEN, et al. 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)[J]. Front. Mater. Sci., 2021, 15(1): 158-165.

URL:

https://academic.hep.com.cn/foms/EN/10.1007/s11706-021-0533-0
https://academic.hep.com.cn/foms/EN/Y2021/V15/I1/158

Fig.1 (a) Molecular structures of FIrpic, BCP, DBP, and C₆₀. (b) Schematic diagram of energy levels of the PHJ device. (c) Device architecture with diagrammatic image for re-emitted FIrpic layer. (d) Absorption spectra of pristine FIrpic, DBP and C₆₀ films; PL spectrum of the FIrpic film on quartz substrates.

Fig.2 (a)J–V characteristics and (b) EQE spectra of ITO/MoO₃ (5 nm)/FIrpic (X nm)/DBP (20 nm)/C₆₀ (40 nm)/BCP (8 nm)/Al (80 nm) with various thicknesses of FIrpic. (c) Dependence of J_sc and V_oc on the FIrpic thickness. (d) Dependence of FF and PCE on the FIrpic thickness.

Tab.1 Photovoltaic characteristics of the PHJs shown in Fig. 2

Fig.3 (a) Absorption spectra and (b) PL spectra excited at 352 nm of FIrpic (X nm)/DBP (20 nm) on quartz substrates. Insets show amplified absorption spectra of FIrpic (X nm)/DBP (20 nm) at 300–380 nm and the PL spectrum of the pristine FIrpic film at 500–650 nm, respectively.

Fig.4 Surface topographic AFM images, 3D AFM images, and Z-axis profiles (from top to bottom) of FIrpic/ITO and DBP/ITO with different film thickness: (a) 3 nm-FIrpic film; (b) 5 nm-FIrpic film; (c) 8 nm-FIrpic film; (d) 10 nm-FIrpic film; (e) 20 nm-DBP film. Scale: 2μm×2μm.

Fig.5 WCA images of FIrpic films with different thickness on the quartz substrate: (a) 3 nm; (b) 5 nm; (c) 8 nm; (d) 10 nm.

Fig.6 (a)Z–V and (b)φ–V transition curves for PHJs with various thickness of FIrpic.

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