Yaoguang Rong

A hole-conductor-free, fully printable mesoscopic perovskite solar cell with high stability

Improved perovskite photovoltaic performance A recent entry in the solar cell race is perovskite cells, named for the structure adopted by salt made from metal halides and organic cations that absorb the light and generate charges. The charges generated have to be transferred to a metal oxide (typically titanium oxide), and some of these charge carriers are lost in the transfer. Mei et al. made this process more efficient by growing a more crystalline perovskite with fewer defects inside porous versions of titanium and zirconium oxide. They added a second organic cation that stuck to the pore walls and directed the growth of the perovskite crystals. The improved solar cells operated for more than 1000 hours under full sunlight. Science, this issue p. 295 A mixed organic phase perovskite grown in mesoporous templates boosts solar cell stability. We fabricated a perovskite solar cell that uses a double layer of mesoporous TiO2 and ZrO2 as a scaffold infiltrated with perovskite and does not require a hole-conducting layer. The perovskite was produced by drop-casting a solution of PbI2, methylammonium (MA) iodide, and 5-ammoniumvaleric acid (5-AVA) iodide through a porous carbon film. The 5-AVA templating created mixed-cation perovskite (5-AVA)x(MA)1-xPbI3 crystals with lower defect concentration and better pore filling as well as more complete contact with the TiO2 scaffold, resulting in a longer exciton lifetime and a higher quantum yield for photoinduced charge separation as compared to MAPbI3. The cell achieved a certified power conversion efficiency of 12.8% and was stable for >1000 hours in ambient air under full sunlight.

Full Printable Processed Mesoscopic CH3NH3PbI3/TiO2 Heterojunction Solar Cells with Carbon Counter Electrode

A mesoscopic methylammonium lead iodide (CH3NH3PbI3) perovskite/TiO2 heterojunction solar cell is developed with low-cost carbon counter electrode (CE) and full printable process. With carbon black/spheroidal graphite CE, this mesoscopic heterojunction solar cell presents high stability and power conversion efficiency of 6.64%, which is higher than that of the flaky graphite based device and comparable to the conventional Au version.

Hole-Conductor-Free Mesoscopic TiO2/CH3NH3PbI3 Heterojunction Solar Cells Based on Anatase Nanosheets and Carbon Counter Electrodes.

A hole-conductor-free fully printable mesoscopic TiO2/CH3NH3PbI3 heterojunction solar cell was developed with TiO2 nanosheets containing high levels of exposed (001) facets. The solar cell embodiment employed a double layer of mesoporous TiO2 and ZrO2 as a scaffold infiltrated by perovskite as a light harvester. No hole conductor or Au reflector was employed. Instead, the back contact was simply a printable carbon layer. The perovskite was infiltrated from solution through the porous carbon layer. The high reactivity of (001) facets in TiO2 nanosheets improved the interfacial properties between the perovskite and the electron collector. As a result, photoelectric conversion efficiency of up to 10.64% was obtained with the hole-conductor-free fully printable mesoscopic TiO2/CH3NH3PbI3 heterojunction solar cell. The advantages of fully printable technology and the use of low-cost carbon-materials-based counter electrode and hole-conductor-free structure provide this design a promising prospect to approach low-cost photovoltaic devices.

Synergy of ammonium chloride and moisture on perovskite crystallization for efficient printable mesoscopic solar cells

Organometal lead halide perovskites have been widely used as the light harvester for high-performance solar cells. However, typical perovskites of methylammonium lead halides (CH3NH3PbX3, X=Cl, Br, I) are usually sensitive to moisture in ambient air, and thus require an inert atmosphere to process. Here we demonstrate a moisture-induced transformation of perovskite crystals in a triple-layer scaffold of TiO2/ZrO2/Carbon to fabricate printable mesoscopic solar cells. An additive of ammonium chloride (NH4Cl) is employed to assist the crystallization of perovskite, wherein the formation and transition of intermediate CH3NH3X·NH4PbX3(H2O)2 (X=I or Cl) enables high-quality perovskite CH3NH3PbI3 crystals with preferential growth orientation. Correspondingly, the intrinsic perovskite devices based on CH3NH3PbI3 achieve an efficiency of 15.6% and a lifetime of over 130 days in ambient condition with 30% relative humidity. This ambient-processed printable perovskite solar cell provides a promising prospect for mass production, and will promote the development of perovskite-based photovoltaics.

Highly ordered mesoporous carbon for mesoscopic CH3NH3PbI3/TiO2 heterojunction solar cell

Highly ordered mesoporous carbon (OMC) with well-connected frameworks was applied in mesoscopic CH3NH3PbI3/TiO2 heterojunction solar cells as counter electrode. The OMC were synthesized by a template method and mixed with flaky graphite to prepare the carbon paste, which was used to fabricate the counter electrode by screen-printing technology. The OMC based solar cell presented a fill factor (FF) of 0.63 and a power conversion efficiency (η) of 7.02%, which was a remarkable improvement compared with the carbon black based device. The electrochemical impedance spectrum measurement demonstrated that the uniform mesopores and interconnected structures in the carbon counter electrode promoted the decrease of charge transfer resistance at the interface and thereby the higher FF and η was obtained.

Transparent NiS counter electrodes for thiolate/disulfide mediated dye-sensitized solar cells

Highly transparent (T% ≈ 90%) nickel sulfide electrodes were prepared by a facile electrodeposition technique to perform as counter electrodes and presented a good photovoltaic performance in thiolate/disulfide mediated dye-sensitized solar cells.

Highly efficient poly(3-hexylthiophene) based monolithic dye-sensitized solar cells with carbon counter electrode

A high efficiency of 3.1% was obtained for poly(3-hexylthiophene) based monolithic solid state dye-sensitized solar cells using graphite/carbon black counter electrodes under simulated AM 1.5 solar illumination of 100 mW cm−2.

Efficient quantum dot-sensitized solar cell with tunable energy band CdSexS(1−x) quantum dots

Tunable energy band CdSexS(1−x) quantum dots (QD) are developed for QD-sensitized solar cells(QDSSCs) by the successive ionic layer adsorption and reaction (SILAR) technique. The results indicated that the energy band and the light absorption of CdSexS(1−x) QDs could be controlled by the ratio of the sulphur (S) and the selenium (Se). Compared with the conventional CdS/CdSe system, its absorption spectrum and monochromatic incident photon-to-electron conversion efficiency (IPCE) spectrum show higher light harvest ability and a broader response wavelength region. As a result, a high energy conversion efficiency of 2.27% was obtained with the CdSexS(1−x) QDSSCs under AM 1.5 illumination of 100 mW cm−2. After being further treated with CdSe QDs, the CdSexS(1−x)/CdSe QDSSC yielded an energy conversion efficiency of 3.17% due to the enhanced absorption and the reduced recombination. It can be expected that tunable energy band QDs controlled by the ratio of atoms can contribute to higher efficiency QDSSCs.

Enhanced electronic properties in CH3NH3PbI3via LiCl mixing for hole-conductor-free printable perovskite solar cells

By mixing perovskite MAPbI3 (MA = CH3NH3+) with LiCl, an effective one-step drop-coating approach was developed to improve the performance of hole-conductor-free printable perovskite solar cells. The LiCl-mixed perovskite exhibited superior electronic properties because of the improved conductivity of the perovskite layer enabling faster electron transport. LiCl-mixing also improved the crystallinity and morphology of the perovskite layer. As a consequence, perovskite solar cells prepared using the LiCl-mixed perovskite as the light harvester produced higher performances compared with the unmixed perovskite, improving the power conversion efficiency from 10.0% to 14.5%.

Mesoporous nitrogen-doped TiO2 sphere applied for quasi-solid-state dye-sensitized solar cell

A mesoscopic nitrogen-doped TiO2 sphere has been developed for a quasi-solid-state dye-sensitized solar cell [DSSC]. Compared with the undoped TiO2 sphere, the quasi-solid-state DSSC based on the nitrogen-doped TiO2 sphere shows more excellent photovoltaic performance. The photoelectrochemistry of electrodes based on nitrogen-doped and undoped TiO2 spheres was characterized with Mott-Schottky analysis, intensity modulated photocurrent spectroscopy, and electrochemical impedance spectroscopy, which indicated that both the quasi-Fermi level and the charge transport of the photoelectrode were improved after being doped with nitrogen. As a result, a photoelectric conversion efficiency of 6.01% was obtained for the quasi-solid-state DSSC.