Identifizierung und Unterdrückung von Grenzfl?chenrekombination für hocheffiziente Perowskit-Solarzellen (SURPRISE II)

Since their discovery in 2009 perovskite photovoltaic (PV) cells have spurred enormous interest due to impressive power conversion efficiencies (PCEs) in combination with the use of moderately pure materials and simple manufacturing techniques. To reach the full efficiency potential of perovskite solar cells, the community has adopted the key principle that one must minimize all non-radiative recombination in the device. However, while the opto-electronic quality of various perovskite absorber layers is close to the radiative limit, the nature of non-radiative transitions at the interfaces remains poorly understood. During the first funding period, the SURPRISE project aimed at unravelling the processes that govern interfacial recombination in high performance pin-type cells with organic charge transport layers (TL), with particular focus on understanding the interfacial recombination pathways, the energy level alignment at the interface, as well as the operation mechanism of interlayers and back-surface fields due to doping. As detailed in section 1.1 below, the team has made substantial progress on these four objectives. The project has also opened up new research directions, by developing advanced opto-electronic characterization methodologies, by identifying a novel operando energy level alignment phenomenon, and by highlighting the role of mobile ions and of the built-in field on device performance. These achievements form a very promising basis for contributing further important advances to the community during the second funding period.
In the proposed follow-up project SURPRISE II, the same team from the first funding period will address demanding research questions of highest topicality with respect to interfacial recombination and defect states. In particular, we will focus on the impact of the grain size, surface and interface chemistry, doping, and crystal strain on the interfacial recombination losses. New research objectives aim at unraveling the impact of interfaces on device ageing and degradation, and the development of advanced experimental methodologies to reliably determine the built-in voltage and the entire solar cells’ band diagram – in the ground state and under operation conditions. Furthermore, we target providing comprehensive understanding of the impact of mobile ions on interfacial recombination, especially with respect to device degradation. Finally, based on our findings in the first funding period with regard to the location of the dominant interfacial recombination loss, point contacts with electron TLs in combination with newly designed interlayers will be developed to reduce the contact area between the perovskite and the TL. Overall, the SURPRISE II project will establish novel principles to systematically mitigate interfacial recombination for efficient and more stable pin-type cells approaching 25% power conversion efficiency.