Seong Sik Shin

Iodide management in formamidinium-lead-halide–based perovskite layers for efficient solar cells

Healing defects with triiodide ions Deep-level defects in organic-inorganic perovskites decrease the performance of solar cells through unproductive recombination of charge carriers. Yang et al. show that introducing additional triiodide ions during the formation of layers of formamidinium lead iodide, which also contain small amounts of methylammonium lead bromide, suppresses the formation of deep-level defects. This process boosts the certified efficiency of 1-cm2 solar cells to almost 20%. Science, this issue p. 1376 Deep-level defect states in formamidinium lead perovskite layers can be minimized by the addition of triiodide ions. The formation of a dense and uniform thin layer on the substrates is crucial for the fabrication of high-performance perovskite solar cells (PSCs) containing formamidinium with multiple cations and mixed halide anions. The concentration of defect states, which reduce a cell’s performance by decreasing the open-circuit voltage and short-circuit current density, needs to be as low as possible. We show that the introduction of additional iodide ions into the organic cation solution, which are used to form the perovskite layers through an intramolecular exchanging process, decreases the concentration of deep-level defects. The defect-engineered thin perovskite layers enable the fabrication of PSCs with a certified power conversion efficiency of 22.1% in small cells and 19.7% in 1-square-centimeter cells.

Colloidally prepared La-doped BaSnO3 electrodes for efficient, photostable perovskite solar cells

Transporter layers for greater stability Although perovskite solar cells (PSCs) can have power conversion efficiencies exceeding 20%, they can have limited stability under ultraviolet irradiation. This is in part because the mesoporous TiO2 used as an electron-transporting layer can photocatalyze unwanted reactions in the perovskite layer. Shin et al. report a low-temperature colloidal method for depositing La-doped BaSnO3 films as a replacement for TiO2 to reduce such ultraviolet-induced damage. Solar cells retained over 90% of their initial performance after 1000 hours of full sun illumination. Science, this issue p. 167 Ultraviolet damage in perovskite photovoltaics induced by TiO2 in the electron-transporting layer can be avoided with La-doped BaSnO3. Perovskite solar cells (PSCs) exceeding a power conversion efficiency (PCE) of 20% have mainly been demonstrated by using mesoporous titanium dioxide (mp-TiO2) as an electron-transporting layer. However, TiO2 can reduce the stability of PSCs under illumination (including ultraviolet light). Lanthanum (La)–doped BaSnO3 (LBSO) perovskite would be an ideal replacement given its electron mobility and electronic structure, but LBSO cannot be synthesized as well-dispersible fine particles or crystallized below 500°C. We report a superoxide colloidal solution route for preparing a LBSO electrode under very mild conditions (below 300°C). The PSCs fabricated with LBSO and methylammonium lead iodide (MAPbI3) show a steady-state power conversion efficiency of 21.2%, versus 19.7% for a mp-TiO2 device. The LBSO-based PSCs could retain 93% of their initial performance after 1000 hours of full-Sun illumination.

Efficient CH3NH3PbI3 Perovskite Solar Cells Employing Nanostructured p‐Type NiO Electrode Formed by a Pulsed Laser Deposition

Highly transparent and nanostructured nickel oxide (NiO) films through pulsed laser deposition are introduced for efficient CH3 NH3 PbI3 perovskite solar cells. The (111)-oriented nanostructured NiO film plays a key role in extracting holes and preventing electron leakage as hole transporting material. The champion device exhibits a power conversion efficiency of 17.3% with a very high fill factor of 0.813.

High-performance flexible perovskite solar cells exploiting Zn2SnO4 prepared in solution below 100 °C.

Fabricating inorganic–organic hybrid perovskite solar cells (PSCs) on plastic substrates broadens their scope for implementation in real systems by imparting portability, conformability and allowing high-throughput production, which is necessary for lowering costs. Here we report a new route to prepare highly dispersed Zn2SnO4 (ZSO) nanoparticles at low-temperature (<100 °C) for the development of high-performance flexible PSCs. The introduction of the ZSO film significantly improves transmittance of flexible polyethylene naphthalate/indium-doped tin oxide (PEN/ITO)-coated substrate from ∼75 to ∼90% over the entire range of wavelengths. The best performing flexible PSC, based on the ZSO and CH3NH3PbI3 layer, exhibits steady-state power conversion efficiency (PCE) of 14.85% under AM 1.5G 100 mW·cm−2 illumination. This renders ZSO a promising candidate as electron-conducting electrode for the highly efficient flexible PSC applications.

Fabrication of Efficient Formamidinium Tin Iodide Perovskite Solar Cells through SnF2–Pyrazine Complex

To fabricate efficient formamidinium tin iodide (FASnI3) perovskite solar cells (PSCs), it is essential to deposit uniform and dense perovskite layers and reduce Sn(4+) content. Here we used solvent-engineering and nonsolvent dripping process with SnF2 as an inhibitor of Sn(4+). However, excess SnF2 induces phase separation on the surface of the perovskite film. In this work, we report the homogeneous dispersion of SnF2 via the formation of the SnF2-pyrazine complex. Consequently, we fabricated FASnI3 PSCs with high reproducibility, achieving a high power conversion efficiency of 4.8%. Furthermore, the encapsulated device showed a stable performance for over 100 days, maintaining 98% of its initial efficiency.

Fabrication of metal-oxide-free CH3NH3PbI3 perovskite solar cells processed at low temperature

Efficient metal-oxide-free perovskite solar cells were successfully developed by employing the N–I–P architecture. The modified solvent engineering process employing a diethylether drip as an orthogonal solvent enabled fabrication of a multi-layered device comprising FTO/PEI/PCBM/MAPbI3/PTAA/Au at low temperature (≤100 °C). Optimization of the thickness of the phenyl-C61-butyric acid methyl ester (PCBM) layer in the planar device yielded an overall power conversion efficiency (PCE) of 15.3% with a large hysteresis but a steady-state efficiency of 13.9% under AM 1.5G 100 mW cm−2 illumination. The use of the low-temperature processed dense-TiO2 layer in conjunction with the PCBM layer gave rise to performance comparable to that of the single electron transport layer (ETL) device and enabled fabrication of an efficient, flexible perovskite solar cell with a PCE of 11.1%.

Improved Quantum Efficiency of Highly Efficient Perovskite BaSnO3-Based Dye-Sensitized Solar Cells

Ternary oxides are potential candidates as an electron-transporting material that can replace TiO₂ in dye-sensitized solar cells (DSSCs), as their electronic/optical properties can be easily controlled by manipulating the composition and/or by doping. Here, we report a new highly efficient DSSC using perovskite BaSnO₃ (BSO) nanoparticles. In addition, the effects of a TiCl₄ treatment on the physical, chemical, and photovoltaic properties of the BSO-based DSSCs are investigated. The TiCl₄ treatment was found to form an ultrathin TiO₂ layer on the BSO surface, the thickness of which increases with the treatment time. The formation of the TiO₂ shell layer improved the charge-collection efficiency by enhancing the charge transport and suppressing the charge recombination. It was also found that the TiCl₄ treatment significantly reduces the amount of surface OH species, resulting in reduced dye adsorption and reduced light-harvesting efficiency. The trade-off effect between the charge-collection and light-harvesting efficiencies resulted in the highest quantum efficiency (i.e., short-circuit photocurrent density), leading to the highest conversion efficiency of 5.5% after a TiCl₄ treatment of 3 min (cf. 4.5% for bare BSO). The conversion efficiency could be increased further to 6.2% by increasing the thickness of the BSO film, which is one of the highest efficiencies from non-TiO₂-based DSSCs.

Tailoring of Electron-Collecting Oxide Nanoparticulate Layer for Flexible Perovskite Solar Cells

Low-temperature-processed perovskite solar cells (PSCs), especially those fabricated on flexible substrates, exhibit device performance that is worse than that of high-temperature-processed PSCs. One of the main reasons for the inferior performance of low-temperature-processed PSCs is the loss of photogenerated electrons in the electron collection layer (ECL) or related interfaces, i.e., indium tin oxide/ECL and ECL/perovskite. Here, we report that tailoring of the energy level and electron transporting ability in oxide ECLs using Zn2SnO4 nanoparticles and quantum dots notably minimizes the loss of photogenerated electrons in the low-temperature-fabricated flexible PSC. The proposed ECL with methylammonium lead halide [MAPb(I0.9Br0.1)3] leads to fabrication of significantly improved flexible PSCs with steady-state power conversion efficiency of 16.0% under AM 1.5G illumination of 100 mW cm(-2) intensity. These results provide an effective method for fabricating high-performance, low-temperature solution-processed flexible PSCs.

BaSnO3 perovskite nanoparticles for high efficiency dye-sensitized solar cells.

The synthesis of highly crystalline perovskite BaSnO3 nanoparticles for use as photoanode materials in dye-sensitized solar cells (DSSCs) is reported, and the photovoltaic properties of DSSCs based on BaSnO3 nanoparticles (BaSnO3 cells) are demonstrated. The resulting DSSCs exhibit remarkably rapid charge collection and a DSSC fabricated with a BaSnO3 film thickness of 43 µm leads to a high energy conversion efficiency of 5.2 %, which is one of the highest reported for ternary oxide-based DSSCs. More importantly, the BaSnO3 cells show superior charge collection in nanoparticle films compared to TiO2 cells and could offer a breakthrough in the efficiencies of DSSCs.

1-D structured flexible supercapacitor electrodes with prominent electronic/ionic transport capabilities.

A highly efficient 1-D flexible supercapacitor with a stainless steel mesh (SSM) substrate is demonstrated. Indium tin oxide (ITO) nanowires are prepared on the surface of the stainless steel fiber (SSF), and MnO2 shell layers are coated onto the ITO/SSM electrode by means of electrodeposition. The ITO NWs, which grow radially on the SSF, are single-crystalline and conductive enough for use as a current collector for MnO2-based supercapacitors. A flake-shaped, nanoporous, and uniform MnO2 shell layer with a thickness of ~130 nm and an average crystallite size of ~2 nm is obtained by electrodeposition at a constant voltage. The effect of the electrode geometry on the supercapacitor properties was investigated using electrochemical impedance spectroscopy, cyclic voltammetry, and a galvanostatic charge/discharge study. The electrodes with ITO NWs exhibit higher specific capacitance levels and good rate capability owing to the superior electronic/ionic transport capabilities resulting from the open pore structure. Moreover, the use of a porous mesh substrate (SSM) increases the specific capacitance to 667 F g(-1) at 5 mV s(-1). In addition, the electrode with ITO NWs and the SSM shows very stable cycle performance (no decrease in the specific capacitance after 5000 cycles).