Iodine and Chlorine Element Evolution in CH₃NH₃PbI_3–<i>x</i>Cl_<i>x</i> Thin Films for Highly Efficient Planar Heterojunction Perovskite Solar Cells

Highly efficient planar heterojunction perovskite solar cells (PHJ–PSCs) with a structure of ITO/PEDOT:PSS/CH₃NH₃PbI_3–<i>x</i>Cl_<i>x</i>/PCBM/C₆₀/Ag was fabricated, in which the compact and pinhole-free CH₃NH₃PbI_3–<i>x</i>Cl_<i>x</i> perovskite thin film was obtained using a mixture of precursors containing lead iodide (PbI₂), lead chloride (PbCl₂), and methylammonium iodide (CH₃NH₃I) at an optimized ratio of 1:1:4. The morphology and formation process of CH₃NH₃PbI_3–<i>x</i>Cl_<i>x</i> thin film was closely related to the annealing temperature and time, which would result in the controllable performance for the PHJ–PSC devices. The morphology, crystallization process, and element analysis suggested that the chlorine gradually diffused and sublimated from the film surface while the iodine moved to the surface, together with the removal of the pinholes in the film. The PHJ–PSCs with the as-prepared CH₃NH₃PbI_3–<i>x</i>Cl_<i>x</i> thin film showed good performance and excellent repeatability. The power conversion efficiency (PCE) up to 14.03% was achieved without obvious hysteresis under different scanning conditions. The understanding of the iodine and chlorine element evolving process during the thermal treatment is beneficial to develop a more efficient scalable one-step solution processing method for fabricating large-area, highly efficient CH₃NH₃PbI_3–<i>x</i>Cl_<i>x</i>-based PSCs

Prominent Efficiency Enhancement in Perovskite Solar Cells Employing Silica-Coated Gold Nanorods

Highly efficient planar heterojunction (PHJ) perovskite solar cells (PSCs) with a structure of ITO/PEDOT:PSS/CH₃NH₃PbI₃/PCBM/Al were fabricated by a low-temperature solution process. As employed silica-coated gold (Au@SiO₂) nanorods at the interface between the hole transport layer PEDOT:PSS and the active layer CH₃NH₃PbI₃, the average power conversion efficiency (PCE) showed over 40% enhancement, of which the average PCE was improved from 10.9% for PHJ-PSCs without Au@SiO₂ to 15.6% for PHJ-PSCs with Au@SiO₂, and the champion one up to 17.6% was achieved. Both experiment and simulation results proved that prominent efficiency enhancement comes from the localized surface plasmon resonance of Au@SiO₂ nanorods which could improve the incident light trapping as well as improve the transport and collection of charge carrier, resulting in the enhancement in device parameters. The results suggest that metal nanorods, e.g., Au@SiO₂, could be employed to fabricate high-efficiency and low-cost PHJ-PSCs

Air-Induced High-Quality CH₃NH₃PbI₃ Thin Film for Efficient Planar Heterojunction Perovskite Solar Cells

Efficient planar heterojunction perovskite solar cells (PHJ–PSCs) with a structure of ITO/PEDOT:PSS/CH₃NH₃PbI₃/PCBM/Al were fabricated using air-induced high-quality CH₃NH₃PbI₃ perovskite thin films, in which the air-inducing process was controlled with a humidity of ∼40%. The air exposure of CH₃NH₃PbI₃ thin films could dramatically improve their properties with large grains and smooth surface, as well as uniform morphology, resulting in an impressive enhancement in carrier lifetime. The ultraviolet photoelectron spectroscopy and X-ray photoelectron spectroscopy results proved that the CH₃NH₃PbI₃ film was <i>n</i>-doped by the absorption of H₂O on the surface but was very stable without obvious degradation for 10 days’ exposure in air. The power conversion efficiency (PCE) of PHJ–PSCs with an air exposure process showed a significant increase up to 16.21% as compared to reference PHJ–PSCs with a PCE of 12.02%. The research work demonstrated that an air-exposure process with a suitable humidity could produce high-quality perovskite thin film for efficient PHJ–PSCs, which may pave a boulevard for fabricating high-efficiency PHJ–PSCs in atmospheric environment

Silane-Capped ZnO Nanoparticles for Use as the Electron Transport Layer in Inverted Organic Solar Cells

Zinc oxide (ZnO) nanoparticles are widely used as electron- transport layer (ETL) materials in organic solar cells and are considered to be the candidate with the most potential for ETLs in roll-to-roll (R2R)-printed photovoltaics. However, the tendency of the nanoparticles to aggregate reduces the stability of the metal oxide inks and creates many surface defects, which is a major barrier to its printing application. With the aim of improving the stability of metal oxide nanoparticle dispersions and suppressing the formation of surface defects, we prepared 3-aminopropyltrimethoxysilane (APTMS)-capped ZnO (ZnO@APTMS) nanoparticles through surface ligand exchange. The ZnO@APTMS nanoparticles exhibited excellent dispersibility in ethanol, an environmentally friendly solvent, and remained stable in air for at least one year without any aggregation. The capping of the ZnO nanoparticles with APTMS also reduced the number of surface-adsorbed oxygen defects, improved the charge transfer efficiency, and suppressed the light-soaking effect. The thickness of the ZnO@APTMS ETL could reach 100 nm without an obvious decrease in the performance. Large-area APTMS-modified ZnO films were successfully fabricated through roll-to-roll microgravure printing and exhibited good performance in flexible organic solar cells. This work demonstrated the distinct advantages of this ZnO@APTMS ETL as a potential buffer layer for printed organic electronics