High efficiency core-shell quantum dot sensitized solar cell using exciplex charge transfer states

28 09 2013

This solar cell has achieved a record conversion efficiency of the quantum dot sensitized solar cells, with a power conversion efficiency of 6.76% (Jsc = 19.59 mA/cm2, Voc = 0.606 V, FF = 0.569)

Core/Shell Colloidal Quantum Dot Exciplex States for the Development of Highly Efficient Quantum Dot Sensitized Solar Cells


Jin Wang , Ivan Mora-Sero , Zhenxiao Pan , Ke Zhao, Hua Zhang , Yaoyu Feng , Guang Yang , Xinhua Zhong , and Juan Bisquert
J. Am. Chem. Soc., Just Accepted Manuscript
DOI: 10.1021/ja4079804

Polymer organic solar cell over 10% efficiency

26 09 2013


Toray Industries Inc has announced a polymer organic thin-film photovoltaic (OPV) cell that is claimed to have world’s highest level of power conversion efficiency of 10.6%.

In construction of the solar cell Toray researchers used a material they have named “Polymer-1” – a thiophene-based polymer material developed by the company – as an electron donor (the equivalent of the p-type semiconductor of inorganic semiconductor). Also the device uses “PCBM70” – which is a C70 derivative – as an electron acceptor (n-type semiconductor).

The HOMO (highest occupied molecular orbital) level and band gap of the Polymer-1 are -5.1eV and 1.58eV, respectively. Its carrier mobility is about 1.0 x 10-2cm2/Vs, which is higher than that of the electron donor material that Toray previously used.

The Toray researchers initially made a 4mm2 OPV cell whose active layer film was just 130nm thick by using Polymer-1 and it produced a power conversion efficiency of 9.4%. Next the researcher made similar size OPV cells but this time they increased the active layer thickness to 300mm with the aim to achieve higher light absorption. What the researchers found was that absorption rates increased for short-wavelengths – and improved the pwer conversion efficiency to 10.6%.

The short-circuit current density, open voltage and fill factor (FF) were 21.7mA/cm2, 0.762 V and 0.641, respectively.

Multitandem record cell

25 09 2013

The Fraunhofer Institute for Solar Energy Systems ISE, Soitec, CEA-Leti and the Helmholtz Center Berlin jointly announced today having achieved a new world record for the conversion of sunlight into electricity using a new solar cell structure with four solar subcells. Surpassing competition after only over three years of research, and entering the roadmap at world class level, a new record efficiency of 44.7% was measured at a concentration of 297 suns. This indicates that 44.7% of the solar spectrum’s energy, from ultraviolet through to the infrared, is converted into electrical energy. This is a major step towards reducing further the costs of solar electricity and continues to pave the way to the 50% efficiency roadmap.

Note that solar cell efficiencies usually reported in this blog are at 1 sun while this cell operates at high concentration of the sunlight (297 suns).

Press Release “World Record Solar Cell with 44.7% Efficiency” [PDF 202.5 kB]

Diffusion-recombination in ChemElectroChem

23 09 2013

The new journal by Wiley ChemElectroChem shows a promising start, focused on energy conversion and storage, under the direction of the experienced editor Greta Heydenrych.

I am grateful to be part of the editorial board of this journal.

We have prepared a paper for the first number. It is an interesting paper in which we have completed the widely used theory of diffusion-recombination impedance. Here we formulate the equations that describe the model in the presence of traps (trap-limited diffusion), and we propose a solution to a problem that plagues the interpretation of impedance spectroscopy results, which is the meaning of parameters in the Gerischer impedance.

Diffusion–Recombination Impedance Model for Solar Cells with Disorder and Nonlinear Recombination

Juan Bisquert, Iván Mora-Sero, Francisco Fabregat-Santiago

DOI: 10.1002/celc.201300091

Record-breaking photovoltaic material

20 09 2013

Today Dr. Victoria Gonzalez-Pedro made the top solar cell in our lab ever. It is a perovskite thin film made by solution processed method, with TiO2 and OMETAD contacts, reaching 11.4% power conversion efficiency under 1 sun light irradiation. It is not a nanostructured cell. This was achieved in a few months by the team working on our group, while the former record was a classical dye solar cell at 9.9%.

Victoria perovskite 20 09 2013

Victoria shows measurement of perovskite solar cell efficiency to 11.4%, 20 09 2013

This is of general interest as it shows that the values presented by leading groups in the last months are at the reach of other labs. The perovskite solar cell is a reality that is here to stay.

2014 MRS Spring Meeting

20 09 2013

Symposium D: Materials for Photoelectrochemical and Photocatalytic Solar-Energy Harvesting and Storage

S14 Meeting Logo

It has been recognized that solar energy will play a critically important role in a sustainable future of humanity. How to harvest solar energy and store it in the form of chemicals for easy transportation and redistribution remains a significant challenge. At the heart of challenge is the lack of suitable materials that can perform the energy-conversion process efficiently and inexpensively. The challenge is particularly acute in approaches based on solution-phase reactions. Compared with solid-state devices such as p-n junction photovoltaic cells, solution-based photoelectrochemical (PEC) solar-energy harvesting processes offer the advantage of low fabrication cost and potential to directly produce fuels, which will solve problems associated with the diurnal nature of sunlight. Examples of solution-based solar-energy conversion approaches include regenerative photoelectrochemical solar cells (such as liquid-junction solar cells, dye- or quantum-dot-sensitized solar cells), photoelectrochemical and photocatalytic water splitting and CO2 photofixation.

To meet the challenge, researchers with diverse backgrounds need to work closely together across different disciplines. This symposium will contribute to such a goal by providing a platform for materials scientists, chemists, physicists and engineers to communicate their vision and the latest exciting new results. Areas to be covered by the symposium will include regenerative photoelectrochemical cells, photoelectrochemical and photocatalytic approaches to water splitting and CO2 photofixation. Because charge behaviors important to solar energy conversion have characteristic lengths on the nanoscale, an emphasis will be placed on the utilization of nanoscale materials such as quantum dots, nanorods, nanowires and hierarchical nanostructures. As organic-dye-based solar cells have evolved into a distinct and flourishing field that is very large, this symposium will not attempt to cover topics related to this approach but instead will focus on emerging new technologies. Speakers from industry and government agencies will also present overviews and perspectives on future solar-energy research.

Topics will include:

  • Photoelectrochemical water splitting
  • Photocatalytic water splitting
  • Regenerative photoelectrochemical solar cells, including quantum-dot-sensitized solar cells, but not dye-sensitized solar cells
  • Photoelectrochemical CO2 fixation
  • Photocatalytic CO2 fixation
  • Artificial photosynthesis

Invited speakers include:

Carlo Bignozzi (Univ. of Ferrara, Italy), Shannon Boettcher (Univ. of Oregon), Emily Cole (Liquid Light), Kazunari Domen (Tokyo Univ., Japan), Heinz Frei (Joint Center for Artificial Photosynthesis), Joseph Hupp (Northwestern Univ.), Thomas Jaramillo (Stanford Univ.),Edson Leite (Federal Univ. of Sao Carlos, Brazil), Nate Lewis (California Inst. of Technology),Jean Manca (Univ. Hasselt, Belgium), Eric Miller (U.S. Dept. of Energy), Emilio Palomares(Inst. Català d’Investigació Química, Spain), Hakan Rensmo (Uppsala Univ., Sweden), John Turner (National Renewable Energy Lab), Heli Wang (National Renewable Energy Lab),Peidong Yang (Univ. of California, Berkeley), Jinhua Ye (National Inst. for Materials Science, Japan), Xiaolin Zheng (Stanford Univ.).

Symposium Organizers

Dunwei Wang
Boston College
2609 Beacon St.
Chestnut Hill, MA 02467

Song Jin
University of Wisconsin-Madison
Dept. of Chemistry
1101 University Ave., Rm. 3363
Madison, WI 53706

Juan Bisquert
Universitat Jaume I
Grup de Dispositius Fotovoltaics i Optoelectrònics
Dept. de Física
12071 Castelló, Spain

Joel W. Ager III
Lawrence Berkeley National Laboratory
Materials Sciences Division
MS 62R0203
1 Cyclotron Rd.
Berkeley, CA 94720


Symposium B: Organic and Inorganic Materials for Dye-Sensitized Solar Cells

S14 Meeting Logo


This symposium will focus on recent progress, current challenges and future directions for dye-sensitized solar-cell technologies. It is recognized that dye-sensitized solar cell (DSC) is one promising technology to be competitive to traditional energy sources and other energy-conversion devices in the future. However, the relatively low efficiency of energy conversion, inadequate understanding of long-term stability, as well as the corrosive nature of iodide-based redox couple, prevent the mass production of DSCs in the marketplace. Recently, significant breakthroughs in energy-conversion efficiencies up to 12.3% for liquid electrolyte-based DSCs and about 12-14% for perovskite-based solid-state DSCs have led this technology to a new paradigm with commercialization not far away. The symposium aims for discussions on advanced organic and inorganic materials that have the potential to address aforementioned challenges.

Topics will include:


  • Advanced light-harvesting materials (organic/inorganic)
  • Innovative electrolyte or hole-conducting systems
  • Efficient counter-electrode or photocathode materials
  • Novel nanostructured semiconducting materials
  • Charge injection, transport and recombination
  • Device modeling and scale-up

tutorial focusing on fundamentals of advanced light-harvesting materials is tentatively planned. Further information will be included in the MRS Program that will be available online in January.


Invited speakers include:

Juan Bisquert (Univ. Jaume I, Spain), Robert Chang (Northwestern Univ.), Eric Wei-Guang Diau (National Chiao Tung Univ., Taiwan), Arthur J. Frank (National Renewable Energy Lab),Liyuan Han (National Inst. for Materials Science, Japan), Joseph T. Hupp (Northwestern Univ.),Prashant V. Kamat (Univ. of Notre Dame), Zhiqun Lin (Georgia Inst. of Technology), Tingli Ma(Dalian Univ. of Technology, China), Nam-Gyu Park (Sungkyunkwan Univ., Korea), Henry J. Snaith (Univ. of Oxford, United Kingdom), He Tian (East China Univ. of Science and Technology, China), Tomas Torres (Univ. Autónoma de Madrid, Spain), Qing Wang (National Univ. of Singapore, Singapore).

Symposium Organizers

Hongshan He
Eastern Illinois University
Dept. of Chemistry
Physical Science, Rm. 3430
600 Lincoln Ave.
Charleston, IL 61920-3099
Tel 217-581-6231

Kai Zhu
National Renewable Energy Laboratory
Chemical and Materials Science Center
1617 Cole Blvd.
Golden, CO 80401
Tel 303-384-6353, Fax 303-384-6150

Jin Young Kim

Korea Institute of Science and Technology
Photo-Electronic Hybrids Research Center
Hwarangno 14-gil 5, Seongbuk-gu
Seoul 136-791, R.O. Korea
Tel 82-2-958-5368, Fax 82-2-958-6649

Zhixin Zhao
Huazhong University of Science and Technology
Wuhan National Laboratory for Optoelectronics
1037 Luoyu Rd.
430074 Wuhan, China
Tel 86-15972183164, Fax 86-27-87793524

Perovskite solar cells: the dual way

16 09 2013

This entry was written by Juan Bisquert and Emilio J. Juárez Pérez

It has been 4 years since Tom Miyasaka and collaborators first reported the use of halide perovskites as a light harvester material in hybrid solar cells (A. Kojima et al., J. Am. Chem. Soc.2009, 131, 6050). This solar cell was originally intended as an alternative to binary lead chalcogenide based sensitized cells. In fact, this early design of the cell was interfaced with a liquid  electrolyte heterojunction like in the classical dye sensitized Grätzel cell. The power conversion efficiency reached a 3.8 % value, which would be quite good for this kind of solar cell in those times, in which quantum dot sensitized solar cell remained at low efficiencies.

Three years after this finding, Nam-Gyu Park and collaborators made two consecutive crucial modifications in the original design (H.S. Kim et al., Sci. Rep. 2012, 2 , 591). They prepared a halide perovskite solution five-fold more concentrated than the original recipe and replaced the liquid hole conductor electrolyte by a solid phase one, the spiro-MeOTAD. The easy manufacture of the active material in this design, that is solution processable and can be synthesized using solutions of simple organic (CH3NH3)I and inorganic PbI2 salts, together with the great power conversion efficiency of 9.7% achieved by Park brought these cells into the scientific community spotlight. Recently Park summarized these developments (Nam-Gyu Park J. Phys. Chem. Lett. 2013 4, 2423-2429).

Currently, there are about 20 published papers dealing with the study of these devices using halide perovskite as light harvester. Over this short period of research time, the scientific experts in solar cells have applied different variations to build up the light active material. The most important developments have been to change the iodide perovskite by a mixed- or bromide based perovskite which develops higher open circuit voltages, to change the organic methylammonium by ethylammonium cation, to substitute spiro-OMeTAD by polymeric hole conductors, to use inert scaffolds for the perovskite like Al2O3 and even do not use them at all, as further explained below.

In the summer of 2013, two major reports have been published showing efficiencies higher than 15%, already raising the attention of photovoltaic industry and investors, but using quite different methods to deposit the halide perovskite.

First Michael Grätzel’s research group discovered (J. Burska et al. Nature, 2013, 499, 316–319) a sequential method that consists of first a stage of spin-coating a concentrated PbI2 solution in a mesoporous layer of TiO2, followed by a second stage of dip-coating the substrate in the organic salt solution of CH3NH3I. They observed that the conversion of PbI2 nanocrystals to CH3NH3PbI3 perovskite was completed in a time of seconds.

Henry Snaith had already shown that one can get rid of the mesostructured electron transporter, using alumnina (an insulator) instead of TiO2 as the nanostructure framework (Lee MM, et al., Science, 2012, 338, 643-647). Last week, he shows in Nature (M. Liu et al. Nature, 2013) how to synthesize the mixed halide perovskite in situ by vapor deposition in a vacuum chamber and overcome the use of a mesoporous layer to scaffold the perovskite. The dual-source evaporation method uses CH3NH3I and PbCl2 to form the mixed halide perovskite CH3NH3PbI3-xClx

In spite of the different active layer deposition techniques, both methods are based on dual precursors, and both designs share the original strategy of capturing electron and holes in the corresponding electrodes by using electron (TiO2 compact layer) and hole (spiro-OMeTAD) selective layers. From the point of view of the manufacturing, the two-step Grätzel approach offers a solution processed, low temperature route that provides efficient use of the reagents and economically feasible techniques to produce cells at industrial scale. The advantage of the Snaith’s method is that the mesoporous layer is unnecessary, showing that the perovskite absorber can stand on its own as any other thin film solar cell. Furthermore he shows in the Nature paper that it is rather difficult to prepare high quality photovoltaic film of single perovskite phase using solution processed methods, due to defficient morphology.

Now there are many scientific teams looking for the highest efficiencies and novel cell architectures. Several groups are also elucidating the mechanisms of transport and accumulation of charges in this challenging two carrier system, and certainly new discoveries and solution to the dilemmas presented now, about the best way to go towards viable large scale production, will appear when the electronic functions are better understood. For the moment it has been shown that the perovskite displays an unprecedented amount of charge accumulation (H. S. Kim et al., Nature Communications 4, 2013, 2242, doi:10.1038/ncomms3242 ).

Thanks to the basic research of a japanese group about five years ago, and several discoveries of people that combined mastery of materials and photovoltaics, effort, wit, and sometimes good luck , an old known halide perovskite compound is waiting that countries and industry environmentally responsible and concerned with the use of renewable energy, willbring economic effort to explore its recently discovered role in the immense future of photovoltaic energy conversion.