EES Blog

Jeffrey Grossman and coworkers communication on 3D solar energy harvesting has been highlighted in ScienceDaily. The MIT researchers modelled and built three-dimensional photovoltaic arrays which are able to provide more energy, more consistently throughout a day. The work was also highlighted in our recent blog article.

Read this HOT communication in full today:

Solar energy generation in three dimensions
Marco Bernardi, Nicola Ferralis, Jin H. Wan, Rachelle Villalon and Jeffrey C. Grossman
Energy Environ. Sci., 2012, DOI: 10.1039/C2EE21170J

US researchers have come up with an explanation for their recent results that show that introducing piezoelectric semiconductor nanowires into solar cells improves their efficiency.

Piezoelectricity is the charge created when certain materials are placed under stress, where compressing or stretching the substance generates electricity. Piezoelectric materials have been used as sensors in cars, as energy scavengers and also as ignition sources in electric lighters. Researchers across the world are working on improving the efficiency of photovoltaic devices, but until recently hadn’t thought of harnessing piezo-potential to do so.

Schematic and energy band diagram of (a) a general nanowire piezoelectric solar cell fabricated using a p-n junction structure. Schematics and energy band diagram of the piezoelectric solar cells under (b) compressive strain and (c) tensile strain, where the polarity and magnitude of the piezopotential can effectively control the carrier generation, separation and transport characteristics. The colour code represents the distribution of the piezopotential at the n-type semiconductor

Interested to know more? Read the full article in Chemistry World here…

Read the Communication from EES: 

Piezo-phototronics effect on nano/microwire solar cells
Yan Zhang ,  Ya Yang and Zhong Lin Wang
Energy Environ. Sci., 2012, Advance Article
DOI: 10.1039/C2EE00057A

Researchers based in Australia have found a way to convert more of the energy from the sun into useful energy, without massively increasing the cost of the process.

Currently photons with energy below a certain threshold are not picked up by most solar cells, but by combining two photons to make a single photon of  higher energy (upconversion) more of the incoming radiation can be utilized.

Schmidt, Lips and co-workers describe a hydrogenated amorphous silicon (a-Si:H) solar cell backed by  a layer of palladium porphyrin capable of upconverting photons, which are then able to be radiated back into the a-Si:H layer and converted to useful energy.

Read this HOT paper in full today:

Improving the light-harvesting of amorphous silicon solar cells with photochemical upconversion
Yuen Yap Cheng, Burkhard Fückel, Rowan W. MacQueen, Tony Khoury, Raphaël G. C. R. Clady, Tim F. Schulze, N. J. Ekins-Daukes, Maxwell J. Crossley, Bernd Stannowski, Klaus Lips and Timothy W. Schmidt
Energy Environ. Sci., 2012, DOI: 10.1039/C2EE21136J

Cost is a major drawback in the current silicon wafer technology used for photovoltaic cells. In this HOT communication Charles Teplin and co-workers report a proof-of concept solar cell using a thin film of crystal silicon grown on an inexpensive CaF₂ “seed” layer.

Read the full details of this exciting Communication:

Biaxially-textured photovoltaic film crystal silicon on ion beam assisted deposition CaF₂ seed layers on glass
James R. Groves , Joel B. Li , Bruce M. Clemens , Vincenzo LaSalvia , Falah Hasoon , Howard M. Branz and Charles W. Teplin
Energy Environ. Sci., 2012, DOI: 10.1039/C2EE21097E

David Mitzi and coworkers at the IBM T. J. Watson Research Center in New York have reported a new Cu₂ZnSn(Se_1–xS_x)₄-type solar cell (where x ≈ 0.03) which has a 10.1% power conversion efficiency. The authors used a liquid processing technique to control the S:Se ratio (and therefore band gap) in the cell.

This type of solar cell is made from elements that are relatively abundant making them good contenders for future affordable power generation from the sun.

Read this HOT article in full today:

Low band gap liquid-processed CZTSe solar cell with 10.1% efficiency
Santanu Bag, Oki Gunawan, Tayfun Gokmen, Yu Zhu, Teodor Todorov and David Mitzi
Energy Environ. Sci., 2012, DOI: 10.1039/C2EE00056C

This paper comes hot on the heels of Professor Henry Snaith’s tutorial paper describing how to accurately measure the efficiency of solar cells. For more details read the full article:

How should you measure your excitonic solar cells?
Henry Snaith
Energy Environ. Sci., 2012, DOI: 10.1039/C2EE03429H

The significance of new solar cell technologies tends to rest heavily on their measured efficiency. But compounding small mistakes in measuring that efficiency can lead to values up to five times higher than the true reading, says Henry Snaith from the University of Oxford, UK. 

Snaith has therefore set out a guide that illustrates the factors that should be taken into consideration when measuring efficiency, and outlines the potential sources of error. It is an attempt to restore confidence in literature claims and make them more easily comparable – both within fields and across different types of cells including dye-sensitised solar cells (DSSCs), organic photovoltaics and hybrid solar cells. The guidance includes how to mask cells to get an accurate measure of the test area; the type of lamps to use and how to calibrate them; and the importance of positioning the cell in exactly the same place as the calibration reference. 

‘There’s an ongoing stream of papers in which it’s not entirely clear exactly how the measurements have been made,’ says Snaith. And worse than that, some papers claim values that appear to be grossly overinflated. That has an impact on genuine claims, Snaith explains. ‘If, for example, someone claims their hybrid solar cell has an efficiency of 4% when it’s really more like 1%, that makes it problematic for someone else to write an exciting paper when they’ve genuinely improved something to 1.5%.’ 

Read the paper from Energy & Environmental Science:

How should you measure your excitonic solar cells?
Henry Snaith
Energy Environ. Sci., 2012, Accepted Manuscript
DOI: 10.1039/C2EE03429H

UK scientists have employed liquid crystals consisting of alternating hydrophobic and hydrophilic layers as a framework for liquid photogalvanic cells.

The system is over five times more solar-to-electrical-power-conversion-efficient-per-pound sterling than dye-sensitised photovoltaic solar cells, whilst being an electrochemical capacitor of high voltage and power efficiency, say the researchers.

Mobile computing devices such as smart phones and tablets require efficient, readily-rechargeable and lightweight power sources that are capable of being moulded into whichever spatial geometry and volume are required for this technology. The integration of solar-rechargeable batteries (such as liquid photogalvanic cells) into such devices increases their portability through reducing dependence on accessible shore power.

Reas the ‘HOT’ paper today:
Photogalvanic Cells Based on Lyotropic Nanosystems: Towards the use of Liquid Nanotechnology for Personalised Energy Sources
J E Halls and J D Wadhawan,
Energy Environ. Sci., 2012, DOI: 10.1039/c2ee03169h

In this ‘HOT’ paper from EES, Michael Grätzel and colleagues investigate the use of platinum-free electrocatalysts in dye-sensitized solar cells (DSSC). This new research has lead to a new record efficiency for an organic redox couple DSSC of 7.9%.

Read Grätzel’s latest paper:

Influence of the counter electrode on the photovoltaic performance of dye-sensitized solar cells using a disulfide/thiolate redox electrolyte
Julian Burschka, Vincent Brault, Shahzada Ahmad, Livain Breau, Mohammad K. Nazeeruddin, Benoît Marsan, Shaik M. Zakeeruddin and Michael Grätzel
Energy Environ. Sci., 2012,
DOI: 10.1039/C2EE03005E