Redox mediators play a major role determining the photocurrent and the photovoltage in dye-sensitized solar cells (DSCs). To maintain the photocurrent, the reduction of oxidized dye by the redox mediator should be significantly faster than the electron back transfer between TiO 2 and the oxidized dye. The driving force for dye regeneration with the redox mediator should be sufficiently low to provide high photovoltages. With the introduction of our new copper complexes as promising redox mediators in DSCs both criteria are satisfied to enhance power conversion efficiencies. In this study, two copper bipyridyl complexes, Cu (II/I) (dmby) 2 TFSI 2/1 (0.97 V vs SHE, dmby = 6,6′-dimethyl-2,2′-bipyridine) and Cu (II/I) (tmby) 2 TFSI 2/1 (0.87 V vs SHE, tmby = 4,4′,6,6′-tetramethyl-2,2′-bipyridine), are presented as new redox couples for DSCs. They are compared to previously reported Cu (II/I) (dmp) 2 TFSI 2/1 (0.93 V vs SHE, dmp = bis(2,9-dimethyl-1,10-phenanthroline). Due to the small reorganization energy between Cu(I) and Cu(II) species, these copper complexes can sufficiently regenerate the oxidized dye molecules with close to unity yield at driving force potentials as low as 0.1 V. The high photovoltages of over 1.0 V were achieved by the series of copper complex based redox mediators without compromising photocurrent densities. Despite the small driving forces for dye regeneration, fast and efficient dye regeneration (2−3 μs) was observed for both complexes. As another advantage, the electron back transfer (recombination) rates were slower with Cu (II/I) (tmby) 2 TFSI 2/1 as evidenced by longer lifetimes. The solar-toelectrical power conversion efficiencies for [Cu(tmby) 2+/1+ based electrolytes were 10.3%, 10.0%, and 10.3%, respectively, using the organic Y123 dye under 1000 W m −2 AM1.5G illumination. The high photovoltaic performance of Cu-based redox mediators underlines the significant potential of the new redox mediators and points to a new research and development direction for DSCs.

For any emerging photovoltaic technology to become commercially relevant, both its power conversion efficiency and photostability are key parameters to be fulfilled. Colloidal quantum dot solar cells are a solution-processed, low-cost technology that has reached efficiency about 9% by judiciously controlling the surface of the quantum dots to enable surface passivation and tune energy levels. However, the role of quantum dot's surface on the stability of these solar cells has remained elusive. Here we report on highly efficient and photostable quantum dot solar cells with efficiencies of 9.6% (and independently certificated values of 8.7%). As a result of optimised surface passivation and suppression of hydroxyl ligands-which are found to be detrimental for both efficiency and photostability-the efficiency remains within 80% after

Dye-sensitized solar cells (DSCs) are molecular photovoltaics that operate efficiently in direct solar and ambient light. The conventional DSC architecture separates the mesoscopic TiO 2 film from the catalytic counter electrode (e.g., Pt) by a spacer. Here, we report on a DSC embodiment employing an advanced structure, where the mesoporous TiO 2 electrode and the poly(3,4ethylenedioxythiophene) counter electrode are directly contacted without using any spacer. This new generation of DSC achieves efficiencies of 13.1% under standard sunlight and 32% under ambient light.

To develop photosensitizers with high open-circuit photovoltage (Voc) is a crucial strategy to enhance the power conversion efficiency (PCE) of co-sensitized solar cells. Here, we show a judiciously tailored organic photosensitizer, coded MS5, featuring the bulky donor N-(2’,4’-bis(dodecyloxy)-[1,1’-biphenyl]-4-yl)-2’,4’-bis(dodecyloxy)-N-phenyl-[1,1’-biphenyl]-4-amine and the electron acceptor 4-(benzo[c][1,2,5]thiadiazol-4-yl)benzoic acid. Employing MS5 with a copper (II/I) electrolyte enables a dye-sensitized solar cell (DSC) to achieve a strikingly high Voc of 1.24 V, with the Voc deficit as low as 130 mV and an ideality factor of merely 1.08. The co-sensitization of MS5 with the wider spectral-response dye XY1b produces a highly efficient and stable DSC with the PCE of 13.5% under standard AM1.5 G, 100 mW cm−2 solar radiation. Remarkably, the co-sensitized solar cell (active area of 2.8 cm2) presents a record PCE of 34.5% under ambient light, rendering it very attractive as an ambient light harvesting energy source for low power electronics.

We report a blue dye, coded as R6, which features a polycyclic aromatic hydrocarbon, 9,19-dihydrobenzo[1',10']phenanthro[3',4':4,5]thieno[3,2-b]benzo[1,10]phenanthro[3,4-d]thiophene, coupled with a diarylamine electron donor and 4-(7-ethynylbenzo[c][1,2,5]thiadiazol-4-yl)benzoic acid acceptor. Dye R6 displays a brilliant sapphire color in a sensitized TiO mesoporous film with a Co(II/III) tris(bipyridyl)-based redox electrolyte. The R6 based dye-sensitized solar cell achieves an impressive power conversion efficiency of 12.6% under standard air mass 1.5 global, 100 mW cm, and shows a remarkable photostability.

The relatively large voltage loss (V loss ) in excitonic type solar cells severely limits their power conversion efficiencies (PCEs). Here, we report a comprehensive control of V loss through efficacious engineering of the sensitizer and redox mediator, making a breakthrough in the PCE of dye-sensitized solar cells (DSSCs).The targeted down-regulation of V loss is successfully realized by three valid channels: (i) reducing the driving force of electron injection through dye molecular engineering, (ii) decreasing the dye regeneration overpotential through redox mediator engineering, and (iii) suppressing interfacial electron recombination.Significantly, the ''trade-off'' effect between the dye optical band gap and the open-circuit voltage (V OC ) is minimized to a great extent, achieving a distinct enhancement in photovoltaic performance (PCE 4 11.5%with V OC up to 1.1 V) for liquid junction cells. The solidification of the best-performing device leads to a PCE of 11.7%, which is so far the highest efficiency obtained for solid-state DSSCs. Our work inspires further development in highly efficient excitonic solar cells by comprehensive control of V loss . Broader contextExcitonic type solar cells, including dye-sensitized solar cells (DSSCs), perovskite solar cells (PSCs) and organic solar cells (OSCs), are potential alternatives for photovoltaic applications. To further advance their power conversion efficiencies (PCEs), it is crucial to reduce the so called voltage loss (V loss ) as much as possible. In DSSCs, the V loss mainly takes place in the electron injection, dye regeneration and interfacial recombination processes, whereas the targeted decreasing of V loss in all these aspects has been rarely reported. To address this issue, we herein demonstrate a comprehensive control of V loss , achieving 11.7% efficiency for solid-state DSSCs. This work is a good example of radically improving the PCE through rationally reducing V loss .

No abstract

11We studied Sr 2 IrO 4 and Sr 3 Ir 2 O 7 using angle-resolved photoemission spectroscopy (ARPES), making direct 12 experimental determinations of intra-and inter-cell coupling parameters as well as Mott correlations and gap sizes.