Understanding charge transfer and recombination by interface engineering for improving the efficiency of PbS quantum dot solar cells†,Nanoscale Horizons

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Understanding charge transfer and recombination by interface engineering for improving the efficiency of PbS quantum dot solar cells†
Nanoscale Horizons ( IF 8.0 ) Pub Date : 2018-03-26 00:00:00 , DOI: 10.1039/c8nh00030a
Chao Ding _{1,

2,

3,

4,

5} , Yaohong Zhang _{1,

2,

3,

4} , Feng Liu _{1,

2,

3,

4} , Yukiko Kitabatake _{4,

6,

7,

8} , Shuzi Hayase _{4,

9,

10,

11,

12} , Taro Toyoda _{1,

2,

3,

4,

12} , Ruixiang Wang _{13,

14,

15,

16} , Kenji Yoshino _{4,

12,

17,

18,

19} , Takashi Minemoto _{4,

12,

17,

18,

20} , Qing Shen _{1,

2,

3,

4,

12}

Affiliation

Faculty of Informatics and Engineering
The University of Electro-Communications
Tokyo 182-8585
Japan
China Scholarship Council
Department of Applied Chemistry
Chuo University
Tokyo 112-8551
Graduate School of Life Science and Systems Engineering
Kyushu Institute of Technology
Fukuoka 808-0196
CREST
Beijing Engineering Research Centre of Sustainable Energy and Buildings
Beijing University of Civil Engineering and Architecture
Beijing 102616
China
Japan Science and Technology Agency (JST)
Saitama 332-0012
Department of Electrical and Electronic Engineering
Department of Photonics

In quantum dot heterojunction solar cells (QDHSCs), the QD active layer absorbs sunlight and then transfers the photogenerated electrons to an electron-transport layer (ETL). It is generally believed that the conduction band minimum (CBM) of the ETL should be lower than that of the QDs to enable efficient charge transfer from the QDs to the collection electrode (here, FTO) through the ETL. However, by employing Mg-doped ZnO (Zn_1−xMg_xO) as a model ETL in PbS QDHSCs, we found that an ETL with a lower CBM is not necessary to realize efficient charge transfer in QDHSCs. The existence of shallow defect states in the Zn_1−xMg_xO ETL can serve as additional charge-transfer pathways. In addition, the conduction band offset (CBO) between the ETL and the QD absorber has been, for the first time, revealed to significantly affect interfacial recombination in QDHSCs. We demonstrate that a spike in the band structure at the ETL/QD interface is useful for suppressing interfacial recombination and improving the open-circuit voltage. By varying the Mg doping level in ZnO, we were able to tune the CBM, defect distribution and carrier concentration in the ETL, which play key roles in charge transfer and recombination and therefore the device performance. PbS QDHSCs based on the optimized Zn_1−xMg_xO ETL exhibited a high power conversion efficiency of 10.6%. Our findings provide important guidance for enhancing the photovoltaic performance of QD-based solar cells.

中文翻译：

通过界面工程了解电荷转移和重组，以提高PbS量子点太阳能电池的效率†

在量子点异质结太阳能电池（QDHSC）中，QD活性层吸收阳光，然后将光生电子转移到电子传输层（ETL）。通常认为，ETL的导带最小值（CBM）应该低于QD的导带最小值，以实现通过ETL从QD到收集电极（此处为FTO）的有效电荷转移。但是，通过在PbS QDHSC中采用掺Mg的ZnO（Zn _{1- x} Mg _x O）作为模型ETL，我们发现具有较低CBM的ETL并不需要在QDHSC中实现有效的电荷转移。Zn _{1− x} Mg _x中存在浅缺陷态O ETL可以充当其他电荷转移途径。此外，首次揭示了ETL和QD吸收剂之间的导带偏移（CBO）对QDHSC中的界面重组产生了重大影响。我们证明，在ETL / QD接口处的能带结构中的尖峰对于抑制界面复合和改善开路电压很有用。通过改变ZnO中的Mg掺杂水平，我们能够调整ETL中的CBM，缺陷分布和载流子浓度，它们在电荷转移和复合以及器件性能中起着关键作用。基于优化的Zn _{1- x} Mg _x的PbS QDHSCO ETL表现出10.6％的高功率转换效率。我们的发现为增强基于量子点的太阳能电池的光伏性能提供了重要的指导。

更新日期：2018-03-26

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