Jie Zhao

Formamidinium lead triiodide (FAPbI₃) is considered as the prospective light-absorbing layer on account of the close-to-ideal bandgap of the α-phase, wide optical absorption spectrum and good thermal stability. Therefore, how to realize δ to α-phase transition to obtain phase-pure α-FAPbI₃ without additives is important for FAPbI₃ perovskite films. Herein, a homologous post-treatment strategy (HPTS) without additives is proposed to prepare FAPbI₃ films with pure α-phase. The strategy is processed along with dissolution and reconstruction process during the annealing. The FAPbI₃ film has tensile strain with the substrate, and the lattice keeps tensile, and the film maintains in an α/δ hybrid phase. The HPTS process releases the tensile strain between the lattice and the substrate. The process of strain release realizes the phase transition from δ to α-phase during this process. This strategy can accelerate the transformation from hexagonal δ-FAPbI₃ to cubic α-FAPbI₃ at 120 °C. As a result, the acquired α-FAPbI₃ films exhibit better film quality in optical and electrical properties, accordingly achieving device efficiency of 19.34% and enhanced stability. This work explores an effective approach to obtain additive-free and phase-pure α-FAPbI₃ films through a HPTS to fabricate uniform high-performance α-FAPbI₃ perovskite solar cells.

Traditional inorganic oxide ferroelectric materials usually have band gaps above 3 eV, leading to more than 80% of the solar spectrum unavailable, greatly limiting the current density of their devices just at μ A cm ⁻² level. Therefore, exploring ferroelectric materials with lower band gaps is considered as an effective method to improve the performance of ferroelectric photovoltaic devices. Inorganic ferroelectric materials are often doped with transition metal elements to reduce the band gap, which is a complex doping and high temperature fabrication process. Recently, molecular ferroelectric materials can change the symmetry and specific interactions of crystals at the molecular level by chemically modifying or tailoring cations with high symmetry, enabling rational design and banding of ferroelectricity in the framework of perovskite simultaneously. Therefore, the molecular ferroelectric materials have a great performance for both excellent ferroelectricity and narrow band gap without doping. Here, we report a ferroelectric photovoltaic device employing an organic-inorganic hybrid molecular ferroelectric material with a band gap of 2.3 eV to obtain high current density. While the poor film quality of molecular ferroelectrics still limits it. The Lewis acid–base adduct is found to greatly improve the film quality with lower defect density and higher carrier mobility. Under standard AM 1.5 G illumination, the photocurrents of ∼1.51 mA cm ⁻² is achieved along with a device efficiency of 0.45%. This work demonstrates new possibilities for the application of molecular ferroelectric films with narrow band gaps in photovoltaic devices, and lays a foundation for Lewis acid–base chemistry to improve the quality of molecular ferroelectric thin films to obtain high current densities and device performance.

Electron transporting layers (ETLs), required to be optically transparent in perovskite solar cells (PSCs) having regular structures, possess a determinant effect on electron extraction and collection. Metal oxides (e.g., TiO₂) have overwhelmingly served as ETLs, but usually have low electron mobility (μ_e < 10⁻² cm² V⁻¹ s⁻¹) not favorable for photovoltaic conversion. Here, metal oxides are replaced with metals (e.g., Ti with μ_e ≈ 294 cm² V⁻¹ s⁻¹) that are sculptured via glancing angle deposition to be a close‐packed nanopillar array (NaPA), which vertically protrudes on a transparent electrode to obtain sufficient optical transmission for light harvesting in perovskite. Ti NaPAs, whose rough surfaces are passivated with 5 nm thick TiO₂ (i.e., Ti NaPAs@TiO₂) to suppress exciton recombination, lead to the champion power conversion efficiency (PCE) of 18.89% that is superior to that of MAPbI₃ PSCs without Ti NaPAs@TiO₂ or containing TiO₂ NaPAs@TiO₂, owing to high surface wettability, high μ_e, and relatively low work function of Ti. Furthermore, Ti NaPAs@TiO₂ effectively prevents the decomposition of MAPbI₃ to achieve long‐term shelf stability whereby 50‐day aging only causes 15% PCE degradation. This work paves the way toward widening the material spectrum, from semiconductors to metals, to generate a diverse range of ETLs for producing efficient optoelectronic devices with long‐term shelf stability.

Conjugated polymer/Si hybrid solar cells are fabricated based on a Si nanowire array (SiNW) substrate prepared by metal-assisted electroless etching.

Hybrid silicon/organic solar cells have been recently extensively investigated due to their simple structure and low-cost fabrication process. However, the efficiency of the solar cells is greatly limited by the barrier height as well as the carrier recombination at the silicon/organic interface. In this work, hydrochloroplatinic acid (H2PtCl6) is employed into the poly(3,4-ethlenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) solution, and the work function (WF) of the PEDOT:PSS layer has been successfully improved. Based on the Pt-modified PEDOT:PSS layer, the efficiency of the silicon/PEDOT:PSS cell can be increased to 11.46%, corresponding to ~20% enhancement to the one without platinum (Pt) modification. Theoretical and experimental results show that, when increasing the WF of the PEDO:PSS layer, the barrier height between the silicon/PEDOT:PSS interface can be effectively enhanced. Meanwhile, the carrier recombination at the interface is significantly reduced. These results can contribute to better understanding of the interfacial mechanism of silicon/PEDOT:PSS interface, and further improving the device performance of silicon/organic solar cells.

Due to the good photocatalytic activity, the TiO2@CNTs thin film is highly desirable to apply to the self-cleaning glass for green intelligent building. Here, the TiO2@CNTs thin film has been successfully achieved by polymer-assisted approach of an aqueous chemical solution method. The polymer, polyethylenimine, aims to combine the Ti4+ with CNTs for film formation of TiO2@CNTs. The resultant thin film was uniform, highly transparent, and super-hydrophilic. Owing to fast electron transport and effectively hindering electron-hole recombination, the TiO2@CNTs thin film has nearly twofold photocatalytic performance than pure TiO2. The TiO2@CNTs thin films show a good application for self-cleaning glasses.

A novel crown ether functionalized ionic liquid has been designed, synthesized and characterized in detail.

In situ thermal polymerization of a model ionic liquid monomer and ionic liquids mixture to form gel electrolytes is developed for quasi‐solid‐state dye‐sensitized solar cells (Q‐DSSCs). The chemical structures and thermal property of the monomers and polymer are investigated in detail. The effect of iodine concentration on the conductivity and triiodide diffusion of the gel electrolytes is also investigated in detail. The conductivity and triiodide diffusion of the gel electrolytes increase with the increasing I₂ concentration, while excessive I₂ contents will decrease the electrical performances. Based on the in situ thermal polymeric gel electrolytes for Q‐DSSCs, highest power conversion efficiency of 5.01% has been obtained. The superior long‐term stability of fabricated DSSCs indicates that the cells based on in situ thermal polymeric gel electrolytes can overcome the drawbacks of the volatile liquid electrolyte. These results offer us a feasible method to explore new gel electrolytes for high‐performance Q‐DSSCs. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42802.