Development of High Efficiency, Spray-Coated Perovskite Solar Cells and Modules Using Additive-Engineered Porous PbI2 Films.

The development of anti-solvent free, scalable, and printable perovskite film is crucial to realizing the low-cost roll-to-roll development of perovskite solar cells (PSCs). Herein, large-area perovskite film fabrication is explored using a spray-assisted sequential deposition technique. How propylene carbonate (PC) solvent additive affects the transformation of lead halide (PbI2 ) into perovskite at room temperature is investigated. The result shows that PC-modified perovskite films exhibit a uniform, pinhole-free morphology with oriented grains compared with pristine perovskite films. The PC-modified perovskite film also has a prolonged fluorescence lifetime that indicates lower carrier recombination. The champion PSC devices based on PC-modified perovskite film realize a power conversion efficiency (PCE) of 20.5% and 19.3% at an active area (A) of 0.09 cm2 and 1 cm2 , respectively. The fabricated PSCs are stable and demonstrate ≥85% PCE retention following 60 days of exposure to ambient conditions. Furthermore, perovskite solar modules (A ≈ 13 cm2 ) that yield a PCE of 15.8% are fabricated. These results are among the best reported for the state-of-art spray-coated PSCs. Spray deposition coupled with a PC additive is highly promising for economical and high-output preparation of PSCs.

Room-Temperature Spray Deposition of Large-Area SnO2 Electron Transport Layer for High Performance, Stable FAPbI3 -Based Perovskite Solar Cells.

The performance and scalability of perovskite solar cells (PSCs) is highly dependent on the morphology and charge selectivity of the electron transport layer (ETL). This work demonstrates a high-speed (1800 mm min-1 ), room-temperature (25 °C-30 °C) deposition of large-area (62.5 cm2 ) tin oxide films using a multi-pass spray deposition technique. The spray-deposited SnO2 (spray-SnO2 ) films exhibit a controllable thickness, a unique granulate morphology and high transmittance (≈85% at 550 nm). The performance of the PSC based on spray-SnO2 ETL and formamidinium lead iodide (FAPbI3 )-based perovskite is highly consistent and reproducible, achieving a maximum efficiency of ≈20.1% at an active area (A) of 0.096 cm2 . Characterization results reveal that the efficiency improvement originates from the granular morphology of spray-SnO2 and high conversion rate of PbI2 in the perovskite. More importantly, spray-SnO2 films are highly scalable and able to reduce the efficiency roll-off that comes with the increase in contact-area between SnO2 and perovskite film. Based on the spray-SnO2 ETL, large-area PSC (A = 1.0 cm2 ) achieves an efficiency of ≈18.9%. Furthermore, spray-SnO2 ETL based PSCs also exhibit higher storage stability compared to the spin-SnO2 based PSCs.

High-performance, color-tunable fiber shaped organic light-emitting diodes.

In recent years, extensive research has been undertaken to develop fiber-shaped optoelectronic devices, because they are aesthetically pleasing, light in weight, and exhibit superior light emitting properties when compared with conventional planar analogues. In this work, we have successfully developed hollow-fiber shaped organic light emitting diodes (HF-OLED) with an exceptionally high luminance and facile color tunability. The HF-OLED device was fabricated by hierarchically depositing amorphous indium-doped tin oxide electrode on a hollow-fiber, followed by the sequential deposition of light-emitting organic layers and Al cathode. The external quantum efficiency of the HF-OLED is more than ∼2.0 times higher than that of a planar-OLED. The experimental results are in good agreement with the output of optical simulations, revealing that the use of a hollow-fiber has contributed to a ∼2.3 times improvement in light extraction efficiency. Furthermore, the color emission of a single HF-OLED device could be easily tuned from a green to yellowish-green wavelength after the injection of a super-yellow solution. The novel color tunable nature of the HF-OLED further broadens its application in the field of modern lighting and display technology.

Controlled Defects of Fluorine-incorporated ZnO Nanorods for Photovoltaic Enhancement.

Anion passivation effect on metal-oxide nano-architecture offers a highly controllable platform for improving charge selectivity and extraction, with direct relevance to their implementation in hybrid solar cells. In current work, we demonstrated the incorporation of fluorine (F) as an anion dopant to address the defect-rich nature of ZnO nanorods (ZNR) and improve the feasibility of its role as electron acceptor. The detailed morphology evolution and defect engineering on ZNR were studied as a function of F-doping concentration (x). Specifically, the rod-shaped arrays of ZnO were transformed into taper-shaped arrays at high x. A hypsochromic shift was observed in optical energy band gap due to the Burstein-Moss effect. A substantial suppression on intrinsic defects in ZnO lattice directly epitomized the novel role of fluorine as an oxygen defect quencher. The results show that 10-FZNR/P3HT device exhibited two-fold higher power conversion efficiency than the pristine ZNR/P3HT device, primarily due to the reduced Schottky defects and charge transfer barrier. Essentially, the reported findings yielded insights on the functions of fluorine on (i) surface -OH passivation, (ii) oxygen vacancies (Vo) occupation and (iii) lattice oxygen substitution, thereby enhancing the photo-physical processes, carrier mobility and concentration of FZNR based device.