Yang Yufeng,Luo Jundong,Luo Ningqi,Wei Aixiang,Liu Jun,Zhao Yu,Xiao Zhiming
In this paper, we report the effect of the Cs + fraction x on the structure, morphology and optical properties of mixed organic–inorganic cation Cs x MA 1− x PbI 3 absorption layers prepared using an anti-solvent-assisted one-step solution deposition method in an ambient environment. By changing the ratios of cesium iodide (CsI) to methyl iodide (MAI) in the precursor solution, the Cs + fraction x varies from 0 to 1. The hole-transporting-material (HTM)-free perovskite solar cells (PSCs) based on the Cs x MA 1− x PbI 3 absorption layers were fabricated in ambient air, and their photovoltaic performance was studied. Results indicate that when the Cs + fraction x is less than 0.3, Cs + ions mainly replace a fraction of MA + ions in the MAPbI 3 lattice and do not lead to a change in the crystal structure of the MAPbI 3 . When the Cs + fraction x is between 0.3 and 0.7, one part of Cs + ions incorporated in the MAPbI 3 lattice replaces MA + ions (α-phase), while the other part forms a yellow photovoltaic-inactive δ-CsPbI 3 phase. The Cs x MA 1− x PbI 3 films with x ≥ 0.8 contain much of the photovoltaic-inactive δ-CsPbI 3 phase. The band gap of the Cs x MA 1− x PbI 3 films increases from 1.53 eV to 1.65 eV with the increase of the Cs + fraction x . The PSCs based on the Cs 0.1 MA 0.9 PbI 3 films exhibit remarkable improvement in device efficiency and stability.
Hole-conductor-free perovskite solar cells (PSCs) based on carbon counter electrode were fabricated under a high humidity air environment and the performance of Cs + doping in methylammonium lead iodide perovskite (Cs x MA 1- x PbI 3 ) as light absorber layer was investigated and discussed. After the doping of Cs + , the excellent morphology, crystallinity and light absorption of perovskite thin films were observed by corresponding test methods, leading to the higher short-circuit current density and open-circuit voltage in the relevant devices. However, excessive Cs + doping can damage the performance of PSCs. The optimized device with x = 0.05, exhibited open-circuit voltage of 956 mV, short-circuit current density of 21.73 mA/cm 2 , fill factor of 0.509 and the power conversion efficiency ( PCE ) of 10.57% under AM 1.5G illumination showing a 16% enhancement than pure MAPbI 3 devices. The PSCs based on carbon counter electrode also showed high stability, despite being stored under ambient air without encapsulation. After 1000 h, the Cs 0.05 MA 0.95 PbI 3 devices maintained more than 90% of their initial PCE . The long-term stability can be attributed to the synergistic interaction of Cs + on the solid solution strengthening of MAPbI 3 and the protection of the hydrophobic carbon electrode on the perovskite active layer.
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