Nearly 100% Photocrosslinking Efficiency in Ultrahigh Work Function Hole-Doped Conjugated Polymers Using
Desmond W Y Teo1, Zaini Jamal1, Hao-Yu Phua2
1Department of Chemistry , National University of Singapore , Lower Kent Ridge Road , S117552 Singapore.
A new photocrosslinking method achieves 100% efficiency for self-compensated hole-doped conjugated polyelectrolytes, enhancing their performance in organic electronic devices without compromising work function. This breakthrough enables flexible device fabrication and improved device efficiency.
Area of Science:
- Materials Science
- Organic Electronics
- Polymer Chemistry
Background:
- Self-compensated (SC) hole-doped conjugated polyelectrolytes offer efficient charge transport for organic semiconductor devices.
- Photocrosslinking these materials could enable wider solvent compatibility for overlayer deposition, enhancing device design flexibility.
- A universal photocrosslinking method for SC hole-doped polyelectrolytes is currently lacking.
Purpose of the Study:
- To develop and demonstrate a generic photocrosslinking methodology for SC hole-doped conjugated polyelectrolytes.
- To investigate the efficiency of photocrosslinking using a specific bis(fluorophenyl azide) photocrosslinker (sFPA82-TfO).
- To evaluate the impact of photocrosslinking on the work function and device performance of these polyelectrolytes.
Main Methods:
- Utilized sFPA82-TfO, an i-line compatible bis(fluorophenyl azide) photocrosslinker.
- Employed a triarylamine-fluorene copolymer (mTFF-C2F5SIS-Na) as the model SC hole-doped polyelectrolyte.
- Conducted molecular dynamics simulations and infrared spectroscopy to understand photocrosslinking mechanisms.
- Fabricated and tested organic diodes (PFOP) and solar cells (PBDTTPD:PC61BM) using the photocrosslinked films.
Main Results:
- Achieved 100% photocrosslinking efficiency for SC hole-doped polyelectrolytes, significantly higher than undoped (20%) or nonconjugated films (20%).
- Preserved the ultrahigh work function (5.75 eV) of the SC hole-doped polyelectrolyte after photocrosslinking.
- Photocrosslinking as a hole-injection layer in PFOP diodes reduced leakage current by over 3 orders of magnitude (to <30 nA cm-2 at ±2 V).
- Photocrosslinking as a hole-collection layer in PBDTTPD:PC61BM solar cells improved photocurrent density, fill factor, and power conversion efficiency.
Conclusions:
- sFPA82-TfO provides an efficient and generic photocrosslinking method for SC hole-doped conjugated polyelectrolytes.
- The high efficiency is attributed to smaller ion multiplet clusters in the doped polymer, preventing crosslinker occlusion.
- Photocrosslinking enhances the performance of organic electronic devices by improving charge injection/collection and reducing leakage current.
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