Correlative Electro-Optical Characterization

To discover novel semiconductors for photovoltaic or other optoelectronic applications, it is essential to first explore and then optimize their electro-optical properties. We have developed an all-in-one setup that allows for automated spectroscopic and transient in-operando testing of optoelectronic devices under various conditions regarding illumination, temperature, and voltage. The obtained results enable us to establish a strong link between device performance parameters and electronic and optical properties of employed materials and interfaces.

Optical table with various light sources, detectors, integrating sphere, and cryostat

Our laboratory offers a wide range of electrical and optical characterizations at the click of a button. Equipped with various light sources, photon detectors, electrical source and measurement units, and controllable environmental chambers, we can analyze photovoltaic devices in multiple modes and under various conditions such as variable:

Temperature
Illumination intensity
Illumination wavelength
Voltage bias
Ambient environment
Time

This allows us to explore their physical properties in greater detail. The key features of our characterization lab are flexibility and versatility. With automated equipment, we can perform successive analyses, sweep through test conditions, and apply different electrical, illumination, and environmental factors during or between measurements. This comprehensive approach enables us to gather more data compared to conventional commercial instruments and is particularly useful, when charactering materials such as perovskites, where the “history” plays an important role.

Available measurement techniques

PL: Photoluminescence spectroscopy measures the emission spectrum of materials and devices upon optical excitation, offering critical insights into the electronic structure.
TRPL: By exciting a material with a short light pulse (<ps width) and measuring the decay of emitted light over time (25ps resolution), Time-Resolved Photoluminescence (TRPL) provides detailed information about carrier lifetimes, recombination mechanisms, and charge transfer. We use the time-correlated single-photon counting (TCSPC) technique.
PLQY: Photoluminescence Quantum Yield (PLQY) is a key metric that measures the efficiency of light emission in a material. It is defined as the ratio of emitted photons to absorbed photons, providing insights into readiative and non-radiative recombinatin processes.
IPCE (EQE): External Quantum Efficiency (EQE) measures the spectral response of a solar cell by quantifying the ratio of collected electron/hole pairs and incident photons. Highly sensitive measurements allow an accurate determination of the absorption onsets and tail states.
EL: Electroluminescence (EL) describes light emission upon applying an electric current to a device. Beyond being the crucial performance meterics of light-emitting diodes, EL provides critical insights into the working principle of solar cells, in particular when employing reciprocity relations between absorption and emission. We are able to measure transient EL, EL spectra and EL yield.
Electrical measurements such as current-voltage curves or transient responses to evaluate efficiency and stability of photovoltaic devices and obtain insights into diode behavior including parasitic effects.
Absorption to determine optical properties such as the bandgap and relate the absorbed photon fluxes to EQE and luminescence.
All these measurements can be performed on full devices and under varied temperature. Spectroscopic measurements such as PL, TRPL, or IPCE can be conducted parallel to applying voltage or current to the device.

Available devices

Illumination sources:

High power 473 nm and 660 nm CW lasers
Supercontinuum pulsed laser with monochromator ranging from 400-1100 nm with adjustable repetition rate 0.15-78 MHz
Variable Blackbody light source up to 1100 K
Calibrated white light source

Photon Detectors:

Spectrometer with Silicon CCD and InGaAs detector to cover visible and NIR range with high resolution (0.25 nm)
Hybrid Photomultiplier Detector with 25 ps resolution for TRPL measurements

Electrical Source & Measure Units:

Two channel Keithley SMU with 0.1 fA & 100 nV resolution
5 GS/s sampling rate oscilloscope

Environmental Chambers:

Helium Cryostat for measurement in vacuum down to 10 K
Probe Station for measurement of small-area devicces and with gas purge and controlled humidity up to 1200 K