Enhanced Charge Carrier Transport and Device Performance Through Dual-Cesium Doping in Mixed-Cation Perovskite Solar Cells with Near Unity Free Carrier Ratios

Fully Inorganic CsSnI3-Based Solar Cells with >6% Efficiency and Enhanced Stability Enabled by Mixed Electron Transport Layer

Fully inorganic black orthorhombic (B-γ) CsSnI₃ has become a promising candidate for perovskite solar cell (PSC) thanks to its low toxicity and decently high theoretical power conversion efficiency (PCE). However, so far, the reported PCE of the B-γ CsSnI₃ PSC is still not comparable with its lead-based or organotin-based counterparts. Herein, a mixed electron transport layer (ETL) composed of ZnO nanoparticles (NPs) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) is incorporated into inverted B-γ CsSnI₃ PSCs. The mixed ETL exhibits the merits of both ZnO and PCBM. The highest PCE of 6.08% was recorded for the PSC with mixed ZnO-PCBM ETL, which is 34.2% higher than that of the device with plain PCBM ETL (PCE of 4.53%) and 28.8% superior to that of plain ZnO ETL-based device (PCE of 4.72%). Meanwhile, the mixed ZnO-PCBM ETL-based PSC retained 71% of its initial PCE under inert conditions at room temperature after 60 days of storage and maintained 67% PCE after 20 days of storage under ambient air at 30% relative humidity and room temperature.

Fabrication of CsxFA1-xPbI3 Mixed-Cation Perovskites via Gas-Phase-Assisted Compositional Modulation for Efficient and Stable Photovoltaic Devices

Over the past few years, significant attention has been focused on HC(NH₂)₂PbI₃ (FAPbI₃) perovskite due to its reduced band gap and enhanced thermal stability compared with the most studied CH₃NH₃PbI₃ (MAPbI₃). However, FAPbI₃ is sensitive to moisture and also encounters a serious structural phase-transition from photoactive α-phase to photoinactive δ-phase. Herein, we first develop a novel FAI gas-phase-assisted mixed-cation compositional modulation method to fabricate Cs_xFA_1-xPbI₃ perovskite solar cells (PSCs), and realize the structural stabilization of α-phase FAPbI₃ with the incorporation of smaller inorganic Cs⁺ ions. Through the setting of different Cs⁺ contents (x = 0, 0.05, 0.10, 0.15, 0.20, 0.25, 0.30, 0.50) along with a moderate FAI vapor deposition process, a series of Cs_xFA_1-xPbI₃ films with consistent compositions are fabricated, which perfectly resolves the main blocking problems of the conventional solution approach, such as difficulty in compositional control and rough film morphology. Meanwhile, we find that the Cs⁺ amount is crucial for generating phase-pure Cs_xFA_1-xPbI₃ (0 < x < 0.30) while higher contents result in phase segregation. Consequently, the optimum amount of Cs⁺ (x = 0.15) is verified, and Cs_0.15FA_0.85PbI₃ shows the smallest unit cell volume and good moisture-resistant feature. Correspondingly, the highest power conversion efficiency (PCE) of 14.45% based on Cs_0.15FA_0.85PbI₃ PSCs is successfully achieved in this work.

A high performance and low-cost hole transporting layer for efficient and stable perovskite solar cells

A F4TCNQ doped FDT HTL based PSC demonstrates 75% higher device stability than a conventional Li-TFSI doped FDT based PSC.