Pt-based ‘Roller-Wheel’ Molecules for Enhanced Solar Cell Performance

Engineering new materials that have valuable and unique optical and electronic properties is of paramount importance for the design of new devices, from memory storage to creating the next generation of organic photovoltaic solar cells.

When designing molecules that possess the traits required for these applications, it is very important to have the ability to measure and quantify the energies and lifetimes of photogenerated excited states. The LP980 Transient Absorption (Flash Photolysis) from Edinburgh Instruments is the only commercially available spectrometer in the world to feature dual detector options for direct kinetic and spectral measurements, which are needed for research into new materials for solar energy conversion.

The Edinburgh Instruments LP980 Spectrometer.

Figure 1. The Edinburgh Instruments LP980 Spectrometer.

Research

Directed by Prof. Yang Qin and Prof. Jeffrey Rack, researchers at the University of New Mexico have designed and synthesized exceptional Pt-based molecular “Roller-wheels” (Figure 2, RWPt). These demonstrated a solar cell power conversion efficiency (PCE) up to 5.9% for the RWPt-2 complex, which is 2% better than any previous Pt-based solar material.

The Pt-based “Roller-Wheel” complexes engineered for solar harvesting studied in this research.

Figure 2. The Pt-based “Roller-Wheel” complexes engineered for solar harvesting studied in this research.

Materials that are Pt-based offer square-planarity and large-spin orbit coupling, giving rise to the large oscillatory strengths of ground and excited states and ordered crystalline structures needed to harness light and shuttle electrons.

The researchers varied the conjugation length of the RWPt complexes systematically and studied the morphology, electrical properties and optical properties using various techniques. These included X-ray diffraction, cyclic-voltammetry, solar device performance and transient absorption. It was discovered that, in the solid state, these molecules pack in a “slip-stack” fashion, which facilitates crystallinity and charge mobility in solar cells.

Transient absorption spectra and lifetimes of RWPt-2 are shown in Figure 3. They show two distinct lifetimes, congruent with two non-interacting localized triplet states gleaned from RWPt-3 and RWPt-1 transient data that exhibits both p-p* and intermolecular charge transfer character. Additional DFT calculations support the formation of these excited states.

Transient absorption spectra and kinetics of RWPt-2, utilising ICCD and PMT detectors on the LP980 Spectrometer.

Figure 3. Transient absorption spectra and kinetics of RWPt-2, utilizing ICCD and PMT detectors on the LP980 Spectrometer.

Conclusion

The Edinburgh Instruments LP980 Transient Absorption Spectrometer is ideally suited to provide these triplet-state measurements for next-generation materials to be used in solar devices because photonic materials for solar cells rely upon the interplay and energetic positions of the singlet and triplet excited state manifolds.

Link to Article: https://pubs.acs.org/doi/abs/10.1021/jacs.7b05801

Figures reprinted with permission from J. Am. Chem. Soc. 2017, 139, 14109-14119.

This information has been sourced, reviewed and adapted from materials provided by Edinburgh Instruments.

For more information on this source, please visit Edinburgh Instruments.

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