Abstract
Effectively suppressing nonradiative recombination at the SnO(2)/perovskite interface is imperative for perovskite solar cells. Although the capabilities of alkali salts at the SnO(2)/perovskite interface have been acknowledged, the effects and optimal selection of alkali metal cations remain poorly understood. Herein, a novel approach for obtaining the optimal alkali metal cation (A-cation) at the interface is investigated by comparatively analyzing different alkali carbonates (A(2)CO(3); Li(2)CO(3), Na(2)CO(3), K(2)CO(3), Rb(2)CO(3), and Cs(2)CO(3)). Theoretical calculations demonstrate that A(2)CO(3) coordinates with undercoordinated Sn and O on the surface, effectively mitigating oxygen vacancy (V(O)) defects with increasing A-cation size, whereas Cs(2)CO(3) exhibits diminished preferability owing to enhanced steric hindrance. The experimental results highlight the crucial role of Rb(2)CO(3) in actively passivating V(O) defects, forming a robust bond with SnO(2), and facilitating Rb(+) diffusion into the perovskite layer, thereby enhancing charge extraction, alleviating deep-level trap states and structural distortion in the perovskite film, and significantly suppressing nonradiative recombination. X-ray absorption spectroscopy analyses further reveal the effect of Rb(2)CO(3) on the local structure of the perovskite film. Consequently, a Rb(2)CO(3)-treated device with aperture area of 0.14 cm(2) achieves a notable efficiency of 22.10%, showing improved stability compared to the 20.11% achieved for the control device.