Stable Inverted Low-Bandgap Polymer Solar Cells with Aqueous Solution Processed Low-Temperature ZnO Buffer Layers

Chunfu Zhang,Ting Heng,Jincheng Zhang,Qubo Jiang,Shangzheng Pang,Gang Lu,Genquan Han,Fengqin He,Hailong You

doi:10.1155/2016/3675036

Abstract

Efficient inverted low-bandgap polymer solar cells with an aqueous solution processed low-temperature ZnO buffer layer have been investigated. The low-bandgap material PTB-7 is employed so that more solar light can be efficiently harvested, and the aqueous solution processed ZnO electron transport buffer layer is prepared at 150°C so that it can be compatible with the roll-to-roll process. Power conversion efficiency (PCE) of the inverted device reaches 7.12%, which is near the control conventional device. More importantly, the inverted device shows a better stability, keeping more than 90% of its original PCE after being stored for 625 hours, while PCE of the conventional device is only 75% of what it was. In addition, it is found that the ZnO thin film annealed in N2can obviously increase PCE of the inverted device further to 7.26%.

Highlights

As an efficient way to utilize the solar energy, solar cells attract great research interests all over the world
The zinc oxide (ZnO) electron transport layer (ETL) is prepared in a low-temperature process so that it can be compatible with the roll-to-roll process
ZnO has the conduction band energy of around −4.3 eV and the valance band energy of around −7.5 eV, which suggests that electrons from PC71BM can be transported into ZnO, while holes from PTB-7 can

Summary

Introduction

As an efficient way to utilize the solar energy, solar cells attract great research interests all over the world. Compared with the conventional structure, inverted PSCs, which are realized by reversing the electrode polarity of the devices, have been considered as an advantageous approach to improving the cell stability and roll-to-roll fabrication process [10,11,12,13,14,15,16,17,18]. In inverted PSCs, the active layer is usually sandwiched by two metal oxide transport layers and a high-work-function metal (Au, Ag, and Cu) acts as the top anode, so the commonly used hole transport layer PEDOT:PSS and low-work-function metal top cathode in conventional structure can be both avoided, all ensuring good stability. We employed the aqueous solution processed ZnO layer as ETL in inverted PSCs based on PTB7:PC71BM blends. The fabricated inverted PSCs show promising performance

Experimental

Results and Discussion

Conclusion