Ferroelectrics Diisopropylammonium Hydrobromide as an Interface Layer Enhancing the Open Circuit Voltage and...

The severe nonradiative recombination losses in Cs₂AgBiBr₆ 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 Cs₂AgBi_0.997Fe_0.003Br₆ film and the hole transport layer Spiro-OMeTAD in Cs₂AgBi_0.997Fe_0.003Br₆ 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 Cs₂AgBi_0.997Fe_0.003Br₆ 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 Cs₂AgBiBr₆ solar cells to date. Moreover, the unencapsulated DIPAB-modified Cs₂AgBi_0.997Fe_0.003Br₆ 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 Cs₂AgBiBr₆ solar cells.