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High-Efficiency Y6 Homojunction Organic Solar Cells Enabled by a Secondary Hole Transport Layer
Shaun McAnally1, Eucalyptus Brooks1, Oliver Lindsay1
1Centre for Organic Photonics & Electronics, School of Chemistry and Molecular Biosciences, The University of Queensland, Brisbane, QLD, 4072, Australia.
Small (Weinheim an Der Bergstrasse, Germany)
|January 31, 2025
Summary
Researchers developed high-efficiency organic solar cells using Y6 small molecules and a novel hole transport layer. This breakthrough achieved a record power conversion efficiency for solution-processed devices, showing minimal performance loss with increased thickness.
Area of Science:
- Materials Science
- Organic Electronics
- Photovoltaics
Background:
- Organic photovoltaics (OPVs) offer potential for low-cost, flexible solar energy.
- Small molecule-based OPVs are attractive for their defined structures and potential for high performance.
- Achieving high power conversion efficiency (PCE) in solution-processed OPVs remains a key challenge.
Purpose of the Study:
- To enhance the performance of Y6 small molecule homojunction organic photovoltaic (OPV) devices.
- To investigate the role of poly[9,9-di-n-octylfluorene-alt-N-(4-sec-butylphenyl)diphenylamine] (TFB) as a secondary hole transport layer.
- To understand the impact of TFB on charge generation and transport in Y6-based OPVs.
Main Methods:
- Fabrication of Y6 homojunction solar cells incorporating TFB as a secondary hole transport layer alongside PEDOT:PSS.
- Device performance characterization, including power conversion efficiency (PCE) measurements.
- Thickness dependence studies of the Y6 active layer.
- Time-resolved photoluminescence (TRPL) and transient absorption spectroscopy (TAS) to probe charge dynamics and interfacial effects.
Main Results:
- A maximum PCE of 2.57% was achieved, representing the highest reported for a solution-processed small molecule homojunction OPV.
- Devices exhibited low thickness dependence, with PCE decreasing only ~17% as active layer thickness increased from 80 to 300 nm.
- TRPL confirmed TFB does not directly contribute to charge generation.
- TAS revealed TFB enhances the formation of long-lived Y6 intermolecular charge-transfer states.
Conclusions:
- The TFB layer effectively acts as an electron blocker and hole extractor, significantly improving OPV performance.
- Careful selection of the electron transport layer (ETL) is crucial to maintain the homojunction integrity and prevent unintended charge generation.
- This work demonstrates a promising strategy for developing high-efficiency, solution-processed small molecule homojunction OPVs.
