Capabilities
Sêr SAM's lab is located at Swansea University's Singleton Campus. The group takes care to deliver state of the art research and results and possesses a variety of apparatuses, many of which were built in-house.
Capabilities
Sêr SAM's lab is located at Swansea University's Singleton Campus. The group takes care to deliver state of the art research and results and possesses a variety of apparatuses, many of which were built in-house.
Ultra-sensitive External Quantum Efficiency (EQE) Measurement
Our home-built, ultra-sensitive EQE measurement setup is a useful tool to investigate photo-generation and absorption processes of charge carriers via inter- and intramolecular states such as charge transfer states or sub-gap tail and trap states in photovoltaic systems based on organic and inorganic semiconductors. Using a high-performance spectrophotometer with integrated double holographic grating monochromators as a probe light source and a low noise multi-stage amplifier system with variable gain and electrical bandwidths enables via lock-in method dynamic ranges of > 100 dB and allows for the detection of photocurrents smaller than femto ampere.
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Our ultra-sensitive EQE measurement setup provides:
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an extended, ultra-low stray light wavelength regime from 175 nm up to 3300 nm
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a pre-current amplifier with variable gain (up to 109 VA-1) and integrated low noise voltage source ( V) for EQE measurements under electrical bias
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electrical bandwidths (integration times) from 106 Hz (1 ms) to Hz (30 ks)
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different pump light sources for EQE measurements under light bias
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low noise sample holder with integrated temperature control stage for temperature dependent EQE measurements
FIgure 1: Experimental setup of our home-built, ultra-sensitive external quantum efficiency (EQE) measurements with spectrophotometer (PerkinElmer, Lambda950, lock-in amplifier (Stanford Research Systems, SR860), multi-blade chopper (Thorlabs, MC2000B), pre-current amplifier (Femto, DLPCA-200) and mounted optics. A detailed description of the measurement setup can be found in [1].
Figure 2: External quantum efficiency (EQE) plotted as a function of wavelength for a 300 nm thick PBTTT:PC70BM device measured under short-circuit (no voltage applied on the device). The EQE measurement was performed at a (probe light) chopping frequency of 273 Hz and an electrical bandwidth of 33.33 mHz. EQE signals above the noise floor at photon energies well below the bandgap reveals sub-gap absorption features which could be assigned to tail or trap states or micro-cavity effect.
References
[1] Zeiske, et al., Sensitivity of Sub-Bandgap External Quantum Efficiency Measurements of Solar Cells under Electrical and Light Bias, ACS Photonics, DOI: 10.1021/acsphotonics.9b01531