The research group of Zhan Xiaowei of the School of Materials has made new progress in the field of organic solar cells

The research group of Zhan Xiaowei of the School of Materials Science and Engineering of Peking University proposed a simple strategy to use strong fluorescent boron-containing organic semiconductor BBS as a solid additive to enhance the exciton diffusion and charge transport in PM6:Y6-based organic solar cells, and improve the energy conversion efficiency of the device.
Mater.
, https://doi.
org/10.
1002/adma.
202205926）
。

As a very promising environment-friendly power generation device, organic solar cells have the advantages of flexibility, light weight and translucency
.
In recent years, thick ring electron receptors represented by ITIC and Y6 have contributed to the transformative development
of this field.
To achieve high efficiency in organic solar cells, the photoactive layer should absorb enough photons to produce excitons, and these excitons must spread rapidly to the interface of the donor and receptor and dissociate effectively into free carriers
.
Therefore, efficient exciton diffusion and charge transport play a crucial role in improving the energy conversion efficiency of organic solar cells
.
Based on the F?rster energy transfer theory, the exciton diffusion length and the photoluminescence quantum yield are positively correlated, so the exciton diffusion length
can be increased by increasing the photoluminescence quantum yield.
Thick ring electron receptors exhibit excellent exciton diffusion behavior, and their exciton diffusion coefficient is two orders of magnitude
higher than that of fullerene receptors.
However, the exciton diffusion length of polymer donors is usually lower than that of the thick ring electron receptor
.
Therefore, increasing the exciton diffusion length of the polymer donor helps to further improve device efficiency
.

The authors utilized strong fluorescent boron-containing organic semiconductor BBS as a solid additive while enhancing exciton diffusion and charge transport
in PM6:Y6-based organic solar cells.
BBS transforms the fluorescence site from more H-type aggregation to more J-type aggregation, which is conducive to the resonance energy transfer of the polymer-donor PM6 exciton diffusion and the energy transfer
of PM6 to Y6.
The measurement results of transient grating ultrafast photoluminescence spectroscopy showed that the addition of BBS improved the exciton diffusion coefficient of PM6 and the dissociation of PM6 excitons
in PM6:Y6:BBS films.
Transient absorption spectroscopy measurements confirm faster charge generation in PM6:Y6:
BBS.
In addition, BBS helps improve Y6 crystallinity, and current sensing atomic force microscopy characterization shows an increase
in carrier diffusion length in PM6:Y6:BBS.
PM6:Y6:BBS-based devices have improved the energy conversion efficiency of 17.
6% due to exciton diffusion, exciton dissociation, enhanced charge generation and charge transport, as well as reduced charge compounding and energy loss, and the energy conversion efficiency of the open-circuit voltage, short-circuit current density and filling factor are simultaneously improved, which is higher than that of the comparison devices without BBS (16.
2%)
.
This work helps to further understand the exciton and charge behavior in non-fullerene organic solar cells, and provides new ideas
for the development of high-performance organic solar cells.

J-V characteristic curve and BBS structure of solar cells

Lu Heng, a doctoral student in Zhan Xiaowei's research group, is the first author of the paper, and Zhan Xiaowei is the corresponding author
.
Co-authors also include Meng Qingbo's research group at the Institute of Physics, Chinese Academy of Sciences, Tang Zheng research group of Donghua University, Ma Wei research group of Xi'an Jiaotong University, Song Yin research group of Beijing Institute of Technology, Justin M.
Hodgkiss research group of Victoria University of Wellington, New Zealand, and Quinn Qiao research group
of Syracuse University in the United States.

This work has been funded
by the National Natural Science Foundation of China and others.

Paper Information:

https://onlinelibrary.
wiley.
com/doi/10.
1002/adma.
202205926?af="R

Simultaneously Enhancing Exciton/Charge Transport in Organic Solar Cells by Organoboron Additive

Heng Lu, Kai Chen, Raja SekharBobba, Jiangjian Shi, Mengyang Li, Yilin Wang, JingweiXue, PeiyaoXue, Xiaojian Zheng, Karen E.
Thorn, Isabella Wagner, Chao-Yang Lin, Yin Song, Wei Ma, Zheng Tang, QingboMeng, Quinn Qiao, Justin M.
Hodgkiss, Xiaowei Zhan*