Our Equipment
Our work consists of two main parts: growing absorbers for thin film solar cells, and determining their efficiency.
The latter is a crucial step in which we perform a detailed analysis of the optical and electronic properties of the solar cells. By measuring these properties, we can identify where energy losses occur and develop strategies to improve the performance of the absorbers.
Growing our absorbers
In our laboratory, we grow the absorbers for our solar cells completely from scratch, starting with a bare Soda-Lime substrate. To achieve this, we utilize three high-vacuum systems that allow for the co- evaporation of elements or compounds. Additionally, we use a tube furnace to anneal precursor films, and for the growth of epitaxial films, we rely on metal-organic vapour phase epitaxy (MOCVD).
processes. We utilize a sputter machine for the metal backcontact, as well as for depositing the ZnO conductive window layer at the front of the cell. To create various buffer materials, we employ chemical bath deposition. Lastly, we use an electron beam evaporator for the deposition of metal grids.
Through these various techniques and machines, we are able to control the growth and composition of our solar cell absorbers to optimize their performance.
Photoluminescence
Our in-house built photoluminescence system is interchangeable between various continious wave lasers with different wavelengths in the visible range, including a supercontinuum white laser used as excitation sources. This system enables intensity and spectral calibration as well as micrometer spatial resolution.
We are able to measure solar cell absorbers at ambient temperature and atmosphere or in a cryostat under vacuum, capable of cooling down to 10K, and in a reaction chamber which can heat up to 400K.
Additionally, we utilize time-correlated single photon counting with a picosecond pulsed laser for time-resolved photoluminescence analysis.
Photospectrometer
We have an integrating sphere photospectrometer and a variable-angle spectral ellipsometer available to accurately measure the optical properties of thin film solar cells. To determine key parameters such as short-circuit current, open-circuit voltage and efficiency, we investigate the cells using current-voltage characteristics under an AAA solar simulator.
Additionally, we measure the spectral quantum efficiency of the current and examine the activation energies at different temperatures.
To understand the impact of defects and doping on performance, we measure the capacitance of the devices at different temperatures, voltages and frequencies ranging from 100 Hz to a few MHz.
Furthermore, a Hall system with a 9T magnet enables us to determine doping densities and electron mobilities.