Lead-free iron-doped Cs3Bi2Br9 perovskite with tunable properties.

Perovskite based on cesium bismuth bromide offers a compelling, non-toxic alternative to lead-containing counterparts in optoelectronic applications. However, its widespread usage is hindered by its wide bandgap. This study investigates a significant bandgap tunability achieved by introducing Fe doping into the inorganic, lead-free, non-toxic, and stable Cs3Bi2Br9 perovskite at varying concentrations. The materials were synthesized using a facile method, with the aim of tuning the optoelectronic properties of the perovskite materials. Characterization through techniques such as X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, energy dispersive spectroscopy (EDS), and UV-vis spectroscopy was conducted to elucidate the transformation mechanism of the doping materials. The substitution process results in a significant change in the bandgap energy, transforming from the pristine Cs3Bi2Br9 with a bandgap of 2.54 eV to 1.78 eV upon 70% Fe doping. The addition of 50% Fe in Cs3Bi2Br9 leads to the formation of the orthorhombic structure in Cs2(Bi,Fe)Br5 perovskite, while complete Fe alloying at 100% results in the phase formation of CsFeBr4 perovskite. Our findings on regulation of bandgap energy and crystal structure through B site substitution hold significant promise for applications in optoelectronics.

Benzophenone: A Small Molecule Additive for Enhanced Performance and Stability of Inverted Perovskite Solar Cells.

In this study, we investigated the impact of benzophenone (BP), a small molecule additive, on the performance and stability of inverted perovskite solar cells (PSCs). Specifically, we introduced BP into the perovskite precursor solution of FAPbI3 to fabricate PSCs with an ITO/PEDOT:PSS/BP:FAPbI3/PCBM/C60/PCB/Ag architecture. The incorporation of BP with an optimum concentration of 2 mg mL-1 significantly enhanced the power conversion efficiency (PCE) of the inverted PSC from 13.12 to 18.84% with negligible hysteresis. Notably, the BP-based PSCs retained ∼90% of their initial PCE after being stored in ambient air with 30% relative humidity at 25 °C for 700 h. In contrast, control devices showed rapid degradation, retaining only 30% of their initial value within 300 h under the same conditions. We attributed the superior performance and stability of the BP-based PSCs to the grain boundary passivation of the perovskite film. The improvement was mainly attributed to the intermolecular interaction between the O-donor Lewis base BP material and both Pb2+ and FA+ in FAPbI3. This effectively suppresses trap-assisted recombination and promotes the conversion of the δ-phase to photoactive and stable α-phase FAPbI3. Overall, our findings suggest that BP is a promising additive for improving the performance and stability of inverted PSCs.