Satyawan Nagane1
University of Cambridge1
Halide perovskite-based solar cells have achieved record-breaking efficiencies of 25.7% in single junction and 32.5% in tandem configurations [1]. Formamidinium (FA) lead triiodide (FAPbI<sub>3</sub>)-based single junction solar cells are the most efficient single junction devices to date. However, the conversion of the black-phase FAPbI<sub>3</sub> perovskite phase to unwanted non-perovskite phase of FAPbI<sub>3</sub> has hindered its widespread acceptance as an absorber for photovoltaic applications. Cation alloying is one of the most efficient routes to stabilize the FA-rich halide perovskite phase. The outstanding example of this is the triple cation, Cs<sub>0.05</sub>FA<sub>0.78</sub>MA<sub>0.17</sub>Pb(I<sub>0.83</sub>Br<sub>0.17</sub>)<sub>3</sub>, composition which has delivered highly reproducible photovoltaic devices with improved ambient stability [2]. Even though this composition delivers highly reproducible devices, this approach is non-ideal as it compromises the bandgap and the mixed-cation and mixed-halide nature can lead to spatial compositional heterogeneities [3]. Here I will reveal the role of functional organic molecule in stabilization of corner-sharing photoactive black phase of pure FAPbI<sub>3</sub>. A functional organic molecule-based approach allows us to stabilize FAPbI<sub>3</sub> perovskite phase without the issues associated with cation alloying. By introducing functional organic molecules into the perovskite precursors, we can template black-phase perovskites that are highly stable in a variety of operational conditions even without any other cation alloying [4]. I’ll step through the mechanism of this additive-assisted stabilization approach and outline the road map from here on to go towards highly efficient, highly stable FAPbI<sub>3</sub> based PV devices.<br/><br/>References:<br/>1. https://www.nrel.gov/pv/assets/pdfs/best-research-cell-efficiencies-rev220630.pdf<br/>2. Saliba, M. et al. Cesium-containing triple cation perovskite solar cells: improved stability, reproducibility and high efficiency. Energy & Environmental Science 2016, 9, 1989–1997.<br/>3. Lu, H. et al. Vapor-assisted deposition of highly efficient, stable black-phase FAPbI<sub>3</sub> perovskite solar cells. Science 370, (2020).<br/>4. Doherty, T.A.S., Nagane, S., et al., Stabilized tilted-octahedra halide perovskites inhibit local formation of performance-limiting phases. Science, 2021, 374, 1598-1605.