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Characterization and Structuring for Perovskite-based Optoelectronics

In the project “REACT-EU - ‘Recovery Assistance for Cohesion and the Territories of Europe’, funds were provided to establish an excellent infrastructure for the characterization of perovskite-based tandem solar cells. This includes standard solar cell characterization methods, such as current-voltage characteristics (IV) and external quantum efficiency (EQE), layer characterization and advanced photoluminescence-based methods. In addition, equipment was procured with which perovskite solar cells can be provided with nanostructures in order to improve efficiency.

The Background

Photovoltaics is set to become the most important energy source for cost-effective climate protection. However, the enormous global expansion will foreseeably lead to challenges, particularly in the area of material and resource availability. In this context, perovskite-based tandem solar cells in particular are a promising technology that promises low resource consumption and low costs. However, further research is also required here in order to bring the technology to market maturity and achieve comprehensive sustainability through innovations based on knowledge.

Research into Perovskite Solar Cells can be roughly divided into Three Stages:

(i) The production of solar cells and the necessary material and process development
(ii) The characterization and measurement of the manufactured materials and solar cells
(iii) The theoretical description and modeling of the underlying physical phenomena and the use of these models to generate approaches for improving solar cell designs

During process development, key layer properties must be precisely adjusted, which requires continuous characterization. These include layer thickness (ellipsometer), conductivity (Hall), and composition (UV-Vis). Solar cells are then produced using the developed processes. These are examined for their efficiency using an IV measuring station and EQE. The long-term stability is then examined in the ageing measuring station. With the PL-based methods (hyperspectral, calibrated, TR-PL), the physical understanding can be deepened and starting points for further improvements can be identified. Building on the initial experiments, nanostructuring will also be used in the medium term to improve efficiency.

High-class equipment is of central importance for success, both in the area of production and in the area of characterization.

The following Equipment was procured as part of the “REACT-EU” Project:

Sun Simulator IV

This setup can be used to measure current-voltage characteristics under sun-like illumination. The illumination is provided by an LED sun simulator. The solar cells are contacted and cooled on a measuring block. Control and measurement are carried out via a four-quadrant power supply integrated with the PC.

EQE Setup

The solar cells are located on a cooled measuring block and are irradiated with monochromatic light while the short-circuit current is measured. The spectral efficiency of the solar cell can be measured by varying the light wavelength.

Ageing Setup

The solar cells are exposed to a defined climate in a chamber (temperature, humidity, oxygen content) and then aged under constant or cyclical lighting and defined electrical conditions (open circuit, short circuit or maximum power point) over long periods of several thousand hours. An IV characteristic curve is measured at regular intervals.

Absolute Calibrated Photoluminescence (PL)

This compact tool is used to measure the photoluminescence in an integrating sphere with absolute calibration. Appropriate evaluation routines can then be used to measure the internal voltage in a semiconductor layer, for example. 

Time-resolved Photoluminescence (PL)

With this self-constructed setup, time-resolved PL signals can be measured even after long periods of continuous illumination.

PL Imaging

With this hyperspectral imaging setup, spatially and spectrally resolved measurements can be carried out. The individual sub-cells of a tandem solar cell can be specifically examined using different light excitations.

UV-Vis Spectrometer

The UV-Vis spectrometer can be used to measure reflection and transmission and thus determine the absorption of the sample and important properties such as the band gap of a semiconductor.

Ellipsometer

With the spectral ellipsometer it is possible to determine the thickness and refractive index of thin layers.

Hall Setup

This Hall measuring station can be used to determine charge carrier density and mobility in semiconductors under varying illumination and temperature.

Hot Press

 For the production of optical nanostructures by transferring lithographically produced stamps onto perovskite and other layers under pressure and heat.