Yongguang Tu

Modulated CH 3 NH 3 PbI 3−x Br x film for efficient perovskite solar cells exceeding 18%

The organic-inorganic lead halide perovskite layer is a crucial factor for the high performance perovskite solar cell (PSC). We introduce CH3NH3Br in the precursor solution to prepare CH3NH3PbI3−xBrx hybrid perovskite, and an uniform perovskite layer with improved crystallinity and apparent grain contour is obtained, resulting in the significant improvement of photovoltaic performance of PSCs. The effects of CH3NH3Br on the perovskite morphology, crystallinity, absorption property, charge carrier dynamics and device characteristics are discussed, and the improvement of open circuit voltage of the device depended on Br doping is confirmed. Based on above, the device based on CH3NH3PbI2.86Br0.14 exhibits a champion power conversion efficiency (PCE) of 18.02%. This study represents an efficient method for high-performance perovskite solar cell by modulating CH3NH3PbI3−xBrx film.

An in situ polymerized PEDOT/Fe3O4 composite as a Pt-free counter electrode for highly efficient dye sensitized solar cells

3,4-Ethylenedioxy thiophene (EDOT) precursor solution doped by Fe3O4 was spin-casted onto fluorine doped tin oxide (FTO) glass and formed poly(3,4-ethylenedioxy thiophene) (PEDOT)/Fe3O4 hybrid films by an in situ polyreaction. The films were utilized as the counter electrode in dye sensitized solar cells (DSSCs). Photoelectric conversion efficiency (PCE) for DSSCs based on PEDOT/Fe3O4 varied with the content of Fe3O4 in the precursor solution. When the content of Fe3O4 was 2 mg ml−1 in the precursor solution (PEDOT/Fe3O4-2), the best performance (8.69%) was obtained. In comparison, that of a DSSC with a Pt counter electrode is 8.35%. According to the surface microtopography and electrochemical analysis, large active areas, consecutive electronic transmission channels and lower charge transfer resistance could be responsible for the high PCE.

Hydrothermal synthesis of CoMoO4/Co9S8 hybrid nanotubes based on counter electrodes for highly efficient dye-sensitized solar cells

CoMoO4/Co9S8 hybrid nanotubes were fabricated by a simple two-step hydrothermal method, which was similar to that for preparing Co9S8 nanotubes. Then the CoMoO4/Co9S8 nanotubes were coated onto fluorine-doped tin oxide glass to fabricate a counter electrode (CE) by spin-casting. Field emission scanning electron microscopy images show that the introduction of CoMoO4 to Co9S8 makes the surface of the CoMoO4/Co9S8 nanotubes rougher. Cyclic voltammetry shows that the electrocatalytic activity of the CoMoO4/Co9S8 CE is similar to that of a Pt CE when the (NH4)2MoO4 content was 60 wt%. Meanwhile, the electrochemical impedance spectroscopy and Tafel measurements demonstrated that the CoMoO4/Co9S8 CE had smaller values of Rs and Rct than a Pt CE. The dye-sensitized solar cells assembled with a CoMoO4/Co9S8 CE achieved excellent values of open-circuit voltage (0.743 V), short-circuit current density (17.276 mA cm−2), fill factor (0.670) and a wonderful power conversion efficiency (8.60%), which is higher than that of DSSCs with a Co9S8 CE (7.69%) or a Pt CE (8.13%) under the light intensity of 100 mW cm−2 (AM 1.5 G).

Solvent engineering for forming stonehenge-like PbI2 nano-structures towards efficient perovskite solar cells

The organic–inorganic lead halide layer is a crucial factor in determining the photovoltaic performance of perovskite solar cells. Based on solvent engineering, we developed a three-step sequential coating method to prepare a high-quality CH3NH3PbI3 layer based on solvent (isopropanol) substitution. Stonehenge-like PbI2 nanostructures with controllable morphology and crystallinity were prepared by solvent substitution instead of the conventional annealing-treatment, affording several channels for CH3NH3I to penetrate into the PbI2 film due to volume expansion, and thus enabling the complete conversion from PbI2 to perovskite. In addition, the device exhibited high reproducibility by our method and achieved a high 17.78% power conversion efficiency under one-sun illumination. Furthermore, we optimized the production craft and successfully fabricated a uniform perovskite film (10 cm × 10 cm) via solvent substitution.

Enhanced photovoltage for inverted planar heterojunction perovskite solar cells

Perovskite layers make the grade Inverted planar perovskite solar cells offer opportunities for a simplified device structure compared with conventional mesoporous titanium oxide interlayers. However, their lower open-circuit voltages result in lower power conversion efficiencies. Using mixed-cation lead mixed-halide perovskite and a solution-processed secondary growth method, Luo et al. created a surface region in the perovskite film that inhibited nonradiative charge-carrier recombination. This kind of solar cell had comparable performance to that of conventional cells. Science, this issue p. 1442 High open-circuit voltages were achieved for planar perovskite solar cells by creating a graded junction. The highest power conversion efficiencies (PCEs) reported for perovskite solar cells (PSCs) with inverted planar structures are still inferior to those of PSCs with regular structures, mainly because of lower open-circuit voltages (Voc). Here we report a strategy to reduce nonradiative recombination for the inverted devices, based on a simple solution-processed secondary growth technique. This approach produces a wider bandgap top layer and a more n-type perovskite film, which mitigates nonradiative recombination, leading to an increase in Voc by up to 100 millivolts. We achieved a high Voc of 1.21 volts without sacrificing photocurrent, corresponding to a voltage deficit of 0.41 volts at a bandgap of 1.62 electron volts. This improvement led to a stabilized power output approaching 21% at the maximum power point.

A gradient engineered hole-transporting material for monolithic series-type large-area perovskite solar cells

Further efficiency enhancement mainly relies on decreasing the interface losses between the active layers in perovskite solar cells. The design of a gradient engineered hole-transporting material is expected to tune the interface losses in perovskite solar cells. In this work, we reported gradient engineering that afforded the hole-transport material (spiro-OMeTAD) dispersed in the upper part of the perovskite layer. Photoluminescence measurements indicated an enhanced hole extraction from the perovskite–spiro-OMeTAD gradient film. And a maximum PCE of 19.16% and a steady-state efficiency of 18.01% were obtained for the small-area device. Furthermore, we assembled monolithic series-type large-area perovskite solar cells based on gradient engineering. The large-area perovskite solar cell with an active area of 1.01 cm2 obtained a PCE of 16.61%. Moreover, monolithic series-type large-area perovskite solar cells showed a Voc of 2.095 V for the binary module and a Voc of 3.104 V for the ternary module, respectively.

High-Performance Molybdenum Diselenide Electrodes Used in Dye-Sensitized Solar Cells and Supercapacitors

Metal dichalcogenide has a layered structure, which is endowed with versatile and tunable photoelectrochemical properties. In this paper, molybdenum diselenide (MoSe2) is synthesized by the solvothermal method, and the as-synthesized MoSe2 shows microsphere hierarchical architecture composed of 2-D nanosheets. The electrochemical characterization indicates that the MoSe2 electrode has lower resistances and better electrocatalytic activity toward triiodide/iodide redox reaction than the traditional Pt electrode. Using the MoSe2 as a counter electrode in the dye-sensitized solar cell (DSSC), a high-power-conversion efficiency of 9.80% is achieved, outperforming the DSSC-based traditional Pt counter electrode (8.17%). Moreover, using the MoSe2 as an electrode in the supercapacitor, it displays a high specific capacitance of 272 F.g-1.

Improved performance of a CoTe//AC asymmetric supercapacitor using a redox additive aqueous electrolyte

Cobalt telluride (CoTe) nanosheets as supercapacitor electrode materials are grown on carbon fiber paper (CFP) by a facile hydrothermal process. The CoTe electrode exhibits significant pseudo-capacitive properties with a highest Cm of 622.8 F g−1 at 1 A g−1 and remarkable cycle stability. A new asymmetric supercapacitor (ASC) is assembled based on CoTe (positive electrode) and activated carbon (negative electrode), which can expand the operating voltage to as high as 1.6 V, and has a specific capacitance of 67.3 F g−1 with an energy density of 23.5 W h kg−1 at 1 A g−1. The performance of the ASC can be improved by introducing redox additive K4Fe(CN)6 into alkaline electrolyte (KOH). The results indicate that the ASC with K4Fe(CN)6 exhibits an ultrahigh specific capacitance of 192.1 F g−1 and an energy density of 67.0 W h kg−1, which is nearly a threefold increase over the ASC with pristine electrolyte.

Diboron-Assisted Interfacial Defect Control Strategy for Highly Efficient Planar Perovskite Solar Cells

Metal halide perovskite films are endowed with the nature of ions and polycrystallinity. Formamidinium iodide (FAI)-based perovskite films, which include large cations (FA) incorporated into the crystal lattice, are most likely to induce local defects due to the presence of the unreacted FAI species. Here, a diboron-assisted strategy is demonstrated to control the defects induced by the unreacted FAI both inside the grain boundaries and at the surface regions. The diboron compound (C12 H10 B2 O4 ) can selectively react with unreacted FAI, leading to reduced defect densities. Nonradiative recombination between a perovskite film and a hole-extraction layer is mitigated considerably after the introduction of the proposed approach and charge-carrier extraction is improved as well. A champion power conversion efficiency of 21.11% is therefore obtained with a stabilized power output of 20.83% at the maximum power point for planar perovskite solar cells. The optimized device also delivers negligible hysteresis effect under various scanning conditions. This approach paves a new way for mitigating defects and improving device performance.