Mixed-organic-cation perovskite photovoltaics have been developed to enhance solar-light harvesting. By using a mixture of formamidinium (FA) and methylammonium (MA) cations in the A position of the APbI3 perovskite structure, researchers achieved improved short-circuit current and device performance compared to those based solely on MA. This approach, previously unexplored in perovskite solar cells, offers a versatile method to tune the structural, electrical, and optoelectronic properties of light-harvesting materials. The study focused on the optical and electronic properties of mixed-cation perovskites, particularly their band gaps and absorption characteristics. The introduction of FA cations in the perovskite structure led to a red shift in the absorption onset, enhancing light harvesting in the red region of the spectrum. This improvement was attributed to the larger size of FA cations, which expanded the crystal lattice and altered the band gap. The researchers demonstrated that the mixed-cation perovskite (MA)0.6(FA)0.4PbI3 exhibited superior photovoltaic performance, with a power conversion efficiency (PCE) of 14.9% under AM1.5G illumination. This was achieved through a sequential deposition method that allowed for precise control over the cation composition and resulted in a higher open-circuit voltage (Voc) and fill factor (FF) compared to traditional methods. The study also highlighted the importance of avoiding the formation of the yellow δ-phase of FAPbI3, which reduced the performance of devices based on pure FA cations. The sequential deposition method effectively prevented this issue while maintaining the red-shifted band gap of FAPbI3. Overall, the use of mixed-cation perovskites offers a promising strategy for improving the efficiency of perovskite solar cells by tuning their optical, electrical, and morphological properties. The findings suggest that further research into mixed-cation perovskites could lead to significant advancements in the performance of perovskite-based photovoltaics.Mixed-organic-cation perovskite photovoltaics have been developed to enhance solar-light harvesting. By using a mixture of formamidinium (FA) and methylammonium (MA) cations in the A position of the APbI3 perovskite structure, researchers achieved improved short-circuit current and device performance compared to those based solely on MA. This approach, previously unexplored in perovskite solar cells, offers a versatile method to tune the structural, electrical, and optoelectronic properties of light-harvesting materials. The study focused on the optical and electronic properties of mixed-cation perovskites, particularly their band gaps and absorption characteristics. The introduction of FA cations in the perovskite structure led to a red shift in the absorption onset, enhancing light harvesting in the red region of the spectrum. This improvement was attributed to the larger size of FA cations, which expanded the crystal lattice and altered the band gap. The researchers demonstrated that the mixed-cation perovskite (MA)0.6(FA)0.4PbI3 exhibited superior photovoltaic performance, with a power conversion efficiency (PCE) of 14.9% under AM1.5G illumination. This was achieved through a sequential deposition method that allowed for precise control over the cation composition and resulted in a higher open-circuit voltage (Voc) and fill factor (FF) compared to traditional methods. The study also highlighted the importance of avoiding the formation of the yellow δ-phase of FAPbI3, which reduced the performance of devices based on pure FA cations. The sequential deposition method effectively prevented this issue while maintaining the red-shifted band gap of FAPbI3. Overall, the use of mixed-cation perovskites offers a promising strategy for improving the efficiency of perovskite solar cells by tuning their optical, electrical, and morphological properties. The findings suggest that further research into mixed-cation perovskites could lead to significant advancements in the performance of perovskite-based photovoltaics.