Ferroelectrics Diisopropylammonium Hydrobromide as an Interface Layer Enhancing the Open Circuit Voltage and Efficiency of Cs ₂ AgBi _0.997 Fe _0.003 Br ₆ Solar Cells

The severe nonradiative recombination losses in Cs 2 AgBiBr 6 solar cells limit the enhancement of their open circuit voltage ( V OC ). Enhancing the built-in electric field (BEF) can help suppress the nonradiative recombination and effectively reduce the V OC and power conversion efficiency (PCE) losses. In this study, we introduced ferroelectrics diisopropylammonium hydrobromide (DIPAB) as an interfacial layer between the Cs 2 AgBi 0.997 Fe 0.003 Br 6 film and the hole transport layer Spiro-OMeTAD in Cs 2 AgBi 0.997 Fe 0.003 Br 6 solar cells. The ferroelectricity of DIPAB increases the BEF significantly. Additionally, the incorporation of DIPAB effectively passivates the defects and optimizes the energy-level alignment. Ultimately, DIPAB-modified Cs 2 AgBi 0.997 Fe 0.003 Br 6 solar cells achieve a PCE enhancement from 2.81% to 3.43% and yield a V OC of up to 1.295 V, which is among the highest V OC documented for Cs 2 AgBiBr 6 solar cells to date. Moreover, the unencapsulated DIPAB-modified Cs 2 AgBi 0.997 Fe 0.003 Br 6 solar cells maintain 86% of its initial PCE after aging for 30 days at 25 ± 5 °C and 60 ± 5% relative humidity and 88% after aging for 300 h at 60 °C in a nitrogen glovebox. This study highlights the significance of ferroelectrics in enhancing the performance and stability of Cs 2 AgBiBr 6 solar cells.