Development of Water-based DSSCs for Printable Flexible Photovoltaic Power Sources

Lead Research Organisation: Imperial College London
Department Name: Chemistry

Abstract

The principal objective of the proposed project is to develop and produce a water-based Dye-Sensitised Solar Cell (DSSC). Also known as Grtzel cells, DSSCs show great potential, being less expensive to manufacture than current solid-state cells and, significantly, they are printable flexible photovoltaic (PV) power sources. They promise substantial breakthroughs in solar energy development and consumer products. Specifically, the project will develop novel water-based DSSCs that will open up new applications, based on the ability to print on flexible plastic substrates and avoid the need for encapsulation. Instead of trying to eliminate water from the system and avoid water ingress, the idea is to create devices that are compatible with water. The development of a water-stable DSSC will overcome limitations in current options, leading to breakthroughs in applications where light weight, flexibility and portability are required (e.g. e-readers, e-fashion, medicine, etc). Elimination or minimization of battery weight will open new market opportunities, particularly as many mobile plastic electronic applications can be expected to experience outdoor or humid indoor conditions.G24i, the first manufacturer of DSSCs using advanced roll-to-roll processing technology, will partner with Imperial College, home to one of the largest programmes in inorganic/organic electronic devices research in the UK. The partners complement one another, combining basic research capabilities with commercialisation and exploitation capabilities, manufacturing capacity and market access.
 
Description Flexible dye sensitized solar cells will require either a very good plastic water barrier (to keep water out) or to be made tolerant of water that diffuses in through the plastic front cover. To study what it takes to make a "water tolerant" dye sensitized solar cells (DSSC), we fabricated DSSCs with high water content electrolytes and studied the types of problems that turned up. We discovered that wetting of the pores with water based electrolytes was a major problem. Current dyes are hydrophobic on the surface, excluding water from the pores. The solution appears to be fabrication of new dyes with hydrophyllic tail groups to make the pores "suck in" water, instead of expelling it. As it turns out, the water barrier is probably a better solution for DSSCs. However, this result is of high importance for those studying solar water splitting using dyes. This latter type of cell must, of course, function in water. Our results on the nature of the dye, dyeing process, and interaction of dye with electrolyte are of key importance in future progress in dye sensitized water splitting.
Exploitation Route yes, those researching dye sensitized water splitting will need to solve some of the same problems. They will find our results and techniques useful.
Sectors Energy
 
Description This project was undertaken to solve a particular issue with the stability of flexible dye sensitized solar cells as under development at the company G24i. The issue was water permeation through the plastic cover on the cells. When the project started, water impermeable plastic layers were a potential solution, but were very expensive. Imperial College and G24i considered an alternate method, invention of dye sensitized solar cells that were not harmed by water. As the project progressed, the cost of water barrier films decreased substantially. It was finally decided by G24i that the cost of developing water tolerant solar cells would be larger than the cost of using the barrier films. Thus, in one sense the project was abandoned. However, a negative outcome is still an outcome, we successfully documented some problems and solutions for water based dye sensitized solar cells, allowing G24i to make a reasoned choice.
First Year Of Impact 2012
Sector Energy
Impact Types Economic
 
Title Dye Adsorption Desorption Method 
Description A method was developed to create homogeneous sub-monolayers of dye molecules on meso-porous TiO2 surfaces. Up to this point people had assumed that the previous methods (short dyeing times, or dilute dye solutions) created this condition. We have shown it does not and provided another method. 
Type Of Material Technology assay or reagent 
Year Produced 2012 
Provided To Others? Yes  
Impact Other groups have used the method, but I would not say there are "notable" results, as the DSSC field has been (temporarily? ) shut down by the rise of methyl ammonium lead perovskite solar cells. 
 
Title TRACER 
Description TRACER (transient and charge extraction robot) has been under development by my group at imperial college since 2007. The TRACER tool consists of a hardware package of "off the shelf" components, a few simple electronic switches and LED light sources that must be fabricated, and a large software package written by myself. The software performs, and automates a large number of unique experiments that have been very useful for research on DSSCs, polymer solar cells. Until 2015 , the design , circuit diagram and software could be downloaded from my imperial college website. That website has been taken down as I am no longer an IC empolyee. over the last few years TRACER instruments have been installed in the other sites in the UK, including Wales and Scotland, in India, Israel, and several in the USA. I do not know how many may have been built without my knowledge. 
Type Of Technology New/Improved Technique/Technology 
Year Produced 2012 
Impact The TRACER has been extremely useful for studying the new methyl ammonium lead iodide solar cells. For these cells, impedance spectroscopy has turned out to be less than useful, and the TRACER is the only other current method.