Purpose
In the past several years, CH3NH3PbI3 perovskite material has been extensively evaluated as an absorber layer of perovskite solar cells due to its excellent structural and optical properties, and greater than 22% conversion efficiency. However, improvement and future commercialization of solar cells based on CH3NH3PbI3 encountered restrictions due to toxicity and instability of the lead element. Recently, studies on properties of lead-free and mixture of lead with other cations perovskite thin films as light absorber materials have been reported. The purpose of this paper was the fabrication of CH3NH3Sn1-xPbxI3 thin films with different SnI2 concentrations in ambient condition, and study on the structural, morphological, optical, and photovoltaic performance of the studied solar cells. The X-ray diffraction studies revealed the formation of both CH3NH3PbI3 and CH3NH3SnI3 phases with increasing the Sn concentration, and improvement in crystallinity and morphology was also observed. All perovskite layers had a relatively high absorption coefficient >104 cm−1 in the visible wavelengths, and the bandgap values varied in the range from 1.46 to 1.63 eV. Perovskite solar cells based on these thin films have been fabricated, and device performance was investigated. Results showed that photo-conversion efficiency (PCE) for the pure CH3NH3PbI3sample was 1.20%. With adding SnI2, PCE was increased to 4.48%.
Design/methodology/approach
In this work, the author mixed tin and lead with different percentages in the perovskite thin film. Also, the preparation of these layers and also other layers to fabricate solar cells based on them were conducted in an open and non-glove box environment. Finally, the effect of [Sn/Pb] ratio in the CH3NH3Sn1-xPbxI3 layers on the structural, morphological, optical, electrical and photovoltaic performance have been investigated.
Findings
CH3NH3Sn1-xPbxI3 (x = 0.0, 0.25, 0.50, 0.75, 1.0) perovskite thin films have been grown by a spin-coating technique. It was found that as tin concentration increases, the X-ray diffraction and FESEM images studies revealed the formation of both CH3NH3PbI3 and CH3NH3SnI3 phases, and improvement in crystallinity, and morphology; all thin films had high absorption coefficient values close to 104 cm−1 in the visible region, and the direct optical bandgap in the layers decreases from 1.63 eV in pure CH3NH3SnI3 to 1.46 eV for CH3NH3Sn0.0.25Pb0.75I3 samples; all thin films had p-type conductivity, and mobility and carrier density increased; perovskite solar cells based on these thin films have been fabricated, and device performance was investigated. Results showed that photo-conversion efficiency (PCE) for the pure CH3NH3PbI3sample was 1.20%. With adding SnI2, PCE was increased to 4.48%.
Originality/value
The preparation method seems to be interesting as it is in an ambient environment without the protection of nitrogen or argon gas.
Long-lived and disorder-free charge transfer states enable endothermic charge separation in efficient non-fullerene organic solar cells
