Trap-Filling of ZnO Buffer Layer for Improved Efficiencies of Organic Solar Cells.

Mingguang Li,Runfeng Chen,Ying Zhang,Longsheng Yu,Yizhong Dai,Wei Huang,Jing Li

doi:10.3389/fchem.2020.00399

Abstract

Trap-assisted recombination loss in the cathode buffer layers (CBLs) is detrimental to the electron extraction process and severely restricts the power conversion efficiencies (PCEs) of organic solar cells (OSCs). Herein, a novel organic–inorganic hybrid film composed of zinc oxide (ZnO) and 2,3,5,6-tetrafluoro-7,7,8, 8-tetracyanoquinodimethane (F4TCNQ) is designed to fill the intrinsic charge traps of ZnO-based CBLs by doping F4TCNQ for high-performance inverted OSCs. Thus, constructed ZnO:F4TCNQ hybrid film exhibits enhanced surface hydrophobicity and adjustable energy levels, providing favorable interfacial condition for electron extraction process. Consequently, trap-assisted recombination loss in the CBLs was efficiently suppressed, leading to the significantly improved fill factor and PCEs of both fullerene- and non-fullerene-based OSCs using the ZnO:F4TCNQ hybrid CBLs. This work illustrates a convenient organic acceptor doping approach to suppress the internal charge traps of traditional inorganic CBLs, which will shed new light on the fabrication of high-performance CBLs with facile electron extraction processes in inverted OSC devices.

Highlights

Bulk heterojunction (BHJ) organic solar cells (OSCs) have attracted extensive attention due to their intrinsic merits of light weight, high mechanical flexibility, and easy processing (Li et al, 2012; Yan et al, 2018)
In order to passivate the inherent defects originated from ZnObased cathode buffer layers (CBLs), we propose an organic–inorganic hybrid CBL composed of inorganic zinc oxide (ZnO) and organic dopant F4TCNQ and explore how the F4TCNQ doping in the CBLs affects device operation
Benefiting from the coordination effect of C=N groups, trap density in the ZnO film is reduced significantly, which suppresses non-geminate charge recombination in the ZnO:F4TCNQ-based OSCs. These results indicate that the construction of novel ZnO:F4TCNQ hybrid film is a promising approach in the interfacial modification of ZnO-based CBLs for the performance optimization of OSC devices

Summary

INTRODUCTION

Bulk heterojunction (BHJ) organic solar cells (OSCs) have attracted extensive attention due to their intrinsic merits of light weight, high mechanical flexibility, and easy processing (Li et al, 2012; Yan et al, 2018). Hybrid CBL consisting of ZnO and poly(2ethyl-2-oxazoline) (PEOz) was constructed and applied to the inverted non-fullerene OSCs. Due to the reduced oxygen deficiency of ZnO by the introduced PEOz, an improved PCE over 12% was achieved (Seo et al, 2018). Various other organic materials such as polyethylenimine (PEI) (Liu C. et al, 2017), fullerene derivatives (Liao et al, 2014; Hu et al, 2016), and non-fullerene acceptors (Xie and Wuerthner, 2017; Li et al, 2019) have been utilized to construct highperformance organic–inorganic hybrid materials by passivating the inherent defects of metal oxide layers and remarkable efficiency improvements were all observed. These results indicate that the construction of novel ZnO:F4TCNQ hybrid film is a promising approach in the interfacial modification of ZnO-based CBLs for the performance optimization of OSC devices

RESULTS AND DISCUSSION

CONCLUSIONS

DATA AVAILABILITY STATEMENT