Influence of SrBr2 Doping on 4T CsPbBr3/Cs0.05(FA0.83MA0.17)0.95Pb(I0.83Br0.17)3 Tandem Device for Underwater Photovoltaic Applications

Underwater photovoltaics plays a pivotal role in photovoltaic applications. However, the underwater solar spectrum differs significantly from that in air, and as water depth increases, solar spectra across various wavebands exhibit distinct attenuation rates. Specifically, the attenuation rate of the red component of sunlight is considerably higher than that of green and blue light (400-600 nm). Thus, under these unique spectral conditions, there is an urgent need to develop stable devices that minimize power conversion efficiency (PCE) loss with increasing water depth. The 4-terminal (4T) structure tandem cell, designed with 2.35 eV CsPbBr₃ and 1.63 eV Cs_0.05(FA_0.83MA_0.17)_0.95Pb(I_0.83Br_0.17)₃, is prioritized due to its suitable optical response range and low PCE loss with increasing water depth. As CsPbBr₃ utilized blue and green light in tandem, which has the highest light intensity underneath water, this study employed doping of SrBr₂ into the CsPbBr₃ film. This approach reduced the defect density of the film, enhanced carrier transport efficiency, and improved the photoelectric responsivity of the device in the 425-500 nm band. The CsPbBr₃ perovskite solar cells that were fabricated demonstrated a high open-circuit voltage of 1.46 V and an exceptional PCE of 7.62%. Additionally, these devices exhibited excellent stability. Consequently, the 4T tandem device achieved PCEs of 15.28, 11.79, and 10.33% at 0, 0.5, and 0.7 m underwater depths respectively, with a variation rate of only 32%. Furthermore, the device demonstrated remarkable stability under working conditions, with an efficiency decay of less than 13% after continuous irradiation for 30 days. These findings suggest that the 4T tandem solar cell holds considerable potential for application in underwater photovoltaics.