High-quality Al-containing chalcopyrites for wide band gap absorbers and solar cells (ALCHESOL)

• Applicant: Professorin Dr. Martina Schmid
• Subject Area: Synthesis and Properties of Functional Materials
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 540263214

The growing world energy demand joined with net zero emission targets urges for the employment of renewable energy resources. Amongst these, photovoltaics stands out due to the abundance of the energy source paired with basically unlimited installation options including water and agricultural land as well as buildings. The highly efficient conversion of sunlight into electricity is thus a central aspect of supporting the energy transition. For the improved exploitation of the solar spectrum, a combination of solar cells with different band gaps is used. Whilst silicon is the most established photovoltaic material with a band gap suitable for the bottom cell, various options exist for the top cell. Amongst these, chalcopyrites are highly interesting due to their stability, high efficiency, and tolerance toward environmental factors of influence. To widen the band gap of the most common chalcopyrite Cu(In,Ga)Se2, indium may be further replaced by gallium, selenium by sulfur, or copper by silver, which however all have limitations and drawbacks. Thus, we will focus on replacing indium with aluminium, a cheap whilst impactful alternative. Early research work has shown the potential of high efficiencies paired with high sub-gap transparency, which is an additional essential requirement for application in semitransparent devices. The further development of the promising material Cu(In,Al)Se2 will first focus on the fabrication of high-quality absorbers, and then on their integration into photovoltaic devices. In this regard, the formation of a material gradient to create e.g. a back surface field fostering charge carrier separation, as well as the integration of alkali salts for improved crystal structure and open circuit voltage will be researched. Furthermore, the tuning of the band alignment at the pn-junction will be investigated by the choice of alternative buffer layers. Finally, the sub-gap transparency is to be optimized, also in relation to a potential reduction of the absorber thickness. By understanding the underlying material properties and device physics, the development of a high-quality Al-containing chalcopyrite with a wide band gap suitable for various applications is aspired. The ultimate goal for the establishment of Cu(In,Al)Se2 material is a sub-gap transparency > 80% and an efficiency comparable to the Cu(In,Ga)Se2 reference when integrated into the device.

• DFG Programme: Research Grants