The lead-free double perovskite Cs2AgBiX6 (X = Br, Cl) has recently demonstrated great potential for applications in solar cells, photodetectors, and X-ray detectors. This material is characterized by a dominant resonant absorption feature in the UV-blue spectral region, which is still under controversial discussion regarding its origin. Here, we uncover an electronic fine structure of this optical feature in Cs2AgBiBr6 thin films. A detailed temperature-resolved study combining photoluminescence (PL), photoluminescence excitation (PLE), and absorption spectroscopy reveals the existence of three optical transitions, situated approximately 100 meV around the resonance at 2.83 eV. PL measurements under pulsed excitation uncover a short-lived blue emission at the absorption resonance energy that persists up to room temperature and indicates the competition of direct emission from the resonant state and fast relaxation into the red emissive ground state. We derive a comprehensive energy scheme and suggest possible mechanisms leading to the observed fine structure splitting.

The microstructure of the metal contact has a significant influence on the PSC aging properties. In this contribution we show that perovskite decomposition and iodide diffusion can be suppressed by using nanocrystalline Ni metallization.

Ferroelectric materials have gained high interest for photovoltaic applications due to their open-circuit voltage not being limited to the band gap of the material. In the past, different lead-based ferroelectric perovskite thin films such as Pb(Zr,Ti)O3 (Pb,La)(Zr,Ti)O3 and PbTiO3 were investigated with respect to their photovoltaic efficiency. Nevertheless, due to their high band gaps they only absorb photons in the UV spectral range. The well-known ferroelectric PbFe0.5Nb0.5O3 (PFN), which is in a structure similar to the other three, has not been considered as a possible candidate until now. We found that the band gap of PFN is around 2.75 eV and that the conductivity can be increased from 23 S/µm to 35 S/µm during illumination. The relatively low band gap value makes PFN a promising candidate as an absorber material.

Introducing a modal system approach for the analytical perovskite thin-film trap physics evaluation. Our study confirms existing models for trap formation in MAPI, substantiating different defect states in the grain boundary and bulk regions.

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