Hysteresis-Suppressed High-Efficiency Flexible Perovskite Solar Cells Using Solid-State Ionic-Liquids for Effective Electron Transport

Significance Statement

Metallic oxides used as electron transport material in perovskite solar cells normally undergo high temperature process to attain their desired structural characteristics. However, the recent incorporation of friendly, low-temperature electron transport material also faces positive demanding situations due to the high cost of production and resultant low electron mobility.

In order to improve this technology, new research must be conducted in view of producing high electron mobility electron transport material, well-suited to a low-temperature process technology coupled with a low-cost production approach.

Researchers led by Professor Shengzhong (Frank) Liu from Shaanxi Normal University in China investigated a solid-state ionic-liquid as an electron transport material with the use of low-temperature processing to attain high efficiency flexible perovskite solar cells with good reproducibility. The research work is now published in the journal, Advanced Materials.

The authors discovered a reduction  in work function of indium-tin-oxide cathode whilst coated with 1-benzyl-3-methylimidazolium chloride solid-state ionic-liquid, enabling electron collection as a result of decreased interface barrier between the cathode and the perovskite absorber. The addition of the solid-state ionic-liquid also led to enhanced short-circuit current density and fill factor in the perovskite solar cells due to their wider bandgap.

The solid-state ionic-liquid coated with flexible poly(ethylene terephthalate)/indium-tin-oxide PET/ITO had a higher transparency and average transmittance approximately 88% in region of 400-450 nm and 400-800 nm respectively compared to the bare samples thereby showing its anti-reflective properties.

The authors were able to provide an appropriate solid-state ionic-liquid layer thickness of flexible perovskite solar cells because of their major role in output performance. A layer thickness of 10nm for the solid-state ionic-liquid was chosen.

Results from current density-voltage curves also showed a higher power conversion efficiency PCE of value 16.09% for perovskite solar cells based on (HC(NH2)2PbI3)0.85(CH3NH3PbBr3)0.15 with the solid-state ionic-liquid as an electron transport material compared with the absent electron transport material. Incident photon-to-current conversion efficiency, short-circuit current density, fill factor and energy levels were also confirmed with higher values.

The authors also discovered a heavily suppressed hysteresis in the current density-voltage. This was attributed to the increase in higher electron mobility as a result of the solid-state ionic-liquid as an electron transport material.

Results from dark current-voltage analysis showed a significant decrease of electron trap density in perovskite films deposited on substrates of the solid-state ionic-liquid coated with indium-tin-oxide which results in a large short-circuit current density.

With these attributes, the solid-state ionic-liquid used in this study as an electron transport material meets the requirement of a low-temperature processing and low-cost manufacturing process favors the technology involved in high efficiency flexible perovskite solar cells.

Reference

Yang, D.1, Yang, R.2, Ren, X.1, Zhu, X.1, Yang, Z.1, Li, C.2, Liu, S.1,2 Hysteresis-Suppressed High-Efficiency Flexible Perovskite Solar Cells Using Solid-State Ionic-Liquids for Effective Electron Transport, Advanced Material 28 (2016) 5206-5213.

Show Affiliations
  1. Key Laboratory of Applied Surface and Colloid Chemistry, National Ministry of Education, Shaanxi Engineering Lab for Advanced Energy Technology, School of Materials Science and Engineering, Shaanxi Normal University, Xi’an, 710119, P. R. China.
  2. Dalian National Laboratory for Clean Energy, iChEM (Collaborative Innovation Center of Chemistry for Energy Materials), Dalian Institute of Chemical Physics, Chinese Academy of Sciences, 457 Zhongshan Road, Dalian, 116023, P. R. China.

 

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