Facile Sol-Gel-Derived Craterlike Dual-Functioning TiO2 Electron Transport Layer for High-Efficiency Perovskite Solar Cells

Sulfonate-Containing Polyelectrolytes for Perovskite Modification: Chemical Configuration, Property, and Performance

Three sulfonate-containing polyelectrolytes are elaborately designed and used to passivate perovskite film with the anti-solvent method. Under the influence of the secondary monomer, three copolymers present various chemical configurations and deliver different modification effects. Fluorene-thiophene copolymer STF has linear and highly-conjugated chain. STF-perovskite film presents large crystal grains. Fluorene-carbazole copolymer SCF has flexible chain and easily enters into grain boundary areas. SCF-perovskite film is homogenous and continuous. Fluorene-fluorene copolymer SPF agglomerates on the surface and is not applicable to the anti-solvent method. The full investigation demonstrates that STF and SCF not only conduct surface defect passivation, but also improve the film quality by being involved in the perovskite's crystallization process. Compared with the control device, the devices with STF and SCF deliver high efficiency and excellent stability. The unencapsulated devices with STF and SCT maintain ≈80% of the initial power conversion efficiency (PCE) after 40 days of storage under 30-40% relative humidity. SCF performs better and the device maintains 60% of the initial PCE after 20 days of storage under 60-80% relative humidity.

Low-Temperature Processed TiOx Electron Transport Layer for Efficient Planar Perovskite Solar Cells

The most frequently used n-type electron transport layer (ETL) in high-efficiency perovskite solar cells (PSCs) is based on titanium oxide (TiO₂) films, involving a high-temperature sintering (>450 °C) process. In this work, a dense, uniform, and pinhole-free compact titanium dioxide (TiO_x) film was prepared via a facile chemical bath deposition process at a low temperature (80 °C), and was applied as a high-quality ETL for efficient planar PSCs. We tested and compared as-deposited substrates sintered at low temperatures (< 150 °C) and high temperatures (> 450 °C), as well as their corresponding photovoltaic properties. PSCs with a high-temperature treated TiO₂ compact layer (CL) exhibited power conversion efficiencies (PCEs) as high as 15.50%, which was close to those of PSCs with low-temperature treated TiO_x (14.51%). This indicates that low-temperature treated TiO_x can be a potential ETL candidate for planar PSCs. In summary, this work reports on the fabrication of low-temperature processed PSCs, and can be of interest for the design and fabrication of future low-cost and flexible solar modules.

TiO2 Nanocolumn Arrays for More Efficient and Stable Perovskite Solar Cells

Organic-inorganic hybrid perovskite solar cells have attracted much attention due to their high power conversion efficiency (>25%) and low-cost fabrication. Yet, improvements are still needed for more stable and higher-performing solar cells. In this work, a series of TiO₂ nanocolumn photonic structures have been intentionally fabricated on half of the compact TiO₂-coated fluorine-doped tin oxide substrate by glancing angle deposition with magnetron sputtering, a method particularly suitable for industrial applications due to its high reliability and reduced cost when coating large areas. These vertically aligned nanocolumn arrays were then applied as the electron transport layer into triple-cation lead halide perovskite solar cells based on Cs_0.05(FA_0.83MA_0.17)_0.95Pb(I_0.83Br_0.17)₃. By comparison to solar cells built onto the same substrate without nanocolumns, the use of TiO₂ nanocolumns can significantly enhance the power conversion efficiency of the perovskite solar cells by 7% and prolong their shelf life. Here, detailed characterizations on the morphology and the spectroscopic aspects of the nanocolumns, their near-field and far-field optical properties, solar cells characteristics, as well as the charge transport properties provide mechanistic insights on how one-dimensional TiO₂ nanocolumns affect the performance of perovskite halide solar cells in terms of charge transport, light harvesting, and stability, knowledge necessary for the future design of higher-performing and more stable perovskite solar cells.

Tin-zinc-oxide nanocomposites (SZO) as promising electron transport layers for efficient and stable perovskite solar cells

Tin-zinc-oxide nanocomposites (SZO) with various Sn : Zn ratios were successfully fabricated and tested as electron transport layers (ETLs) in perovskite solar cells (PVSCs). The fabricated nanocomposites showed good crystallinity, good contact between layers, good electrical conductivity, and favorable light absorption, resulting in an enhancement in the net efficiency of CH3NH3PbI3 (MAPI)-based perovskite solar cells. The device made of SZO-Sn0.05 as an ETL showed a maximum power conversion efficiency (PCE) of 17.81% with a short-circuit current density (J sc) of 23.59 mA cm-2, an open-circuit voltage (V oc) of 1 V, and a fill factor (FF) of 0.754. However, the ETL containing lower Sn ratios showed PCEs of 12.02, 13.80 and 15.86% for pure ZnO, SZO-Sn0.2 and SZO-Sn0.1, respectively. Meanwhile, the reproducibility of 30 fabricated devices proved the outstanding long-term stability of the cells based on SZO nanocomposites, retaining ≈85% of their PCE over 1200 h of operation. In addition, the incident-photon-to-current efficiency (IPCE) exceeded 90% over the entire wavelength range from 400 to 800 nm. The enhancement in the PCE of the fabricated PVSCs can be ascribed to the large surface area of the SZO nanoparticles, high charge extraction efficiency, and suppression of charge recombination provided by SnO x . The current results suggest that our synthesized tin-zinc-oxide nanocomposite is an effective electron transport layer for efficient and stable perovskite solar cells.