Defect Passivation in Polycrystalline Perovskites for Efficient Tandem Solar Cells
Kai Zhu a
a National Renewable Energy Laboratory Denver
Invited Speaker, Kai Zhu, presentation 030
Publication date: 14th October 2019

Single-junction perovskite solar cells (PSCs) have demonstrated unprecedentedly high efficiency of >25% among all polycrystalline thin-film PV technologies. Developing perovskite-based tandem devices represents the next step for further improving the perovskite-based solar cells beyond the theoretical efficiency limit for single-junction devices. The bandgap tunability through perovskite composition engineering is attractive for developing ultrahigh-efficiency tandem solar cells, including perovskite/perovskite, perovskite/silicon, or perovskite/thin-film absorber (e.g., CIGS). Here, I will present our recent progress on a few strategies for defect passivation in polycrystalline perovskites including wide-bandgap (~1.7–1.8 eV) and low-bandgap (~1.2–1.3 eV) perovskite absorbers. The challenge for wide-bandgap PSCs is to reduce the voltage deficit, which requires strategies for suppressing defect density. The key challenges for low-bandgap Sn-Pb based PSCs lie at both the material and device levels. The high defect density associated with oxidation of Sn2+ to Sn4+ and formation of Sn vacancies significantly limits carrier lifetime and charge collection. I will discuss these challenges and show our recent progress on the general approaches to reduce defect density in perovskites for both low- and wide-bandgap perovskite films. The precursor chemistry and growth conditions affect significantly the physical and optoelectronic properties of perovskites. Applications of perovskite absorbers in highly efficient tandem devices will be discussed. These results and others will be discussed.

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