FITS

FIGURE 5. Illustrates how the generalized logistic growth function fits with an EG device (A) an EGL device (B) .

Data AnalysisAll the data from each experiment was transported to

Microsoft Excel to perform non-linear regression analysis using the Solver program. The generalized logistic growth function5

(1)

was used to characterize the photocurrents of each device where A is the initial current, K is the final current, and B is the growth .rate.

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Investigating the influence of lithium intercalation on dispersive electron mobility kinetics in dye-sensitized solar cells

INTRODUCTION

Dye-sensitized solar cells (DSSCs) are a type of solar cell that use a nanocrystalline semiconductor film sensitized with an efficient light absorbing molecule1. An electron is transferred from the photo-excited dye molecule to an acceptor state within the semiconductor. This study examines the transport of the photo-injected electrons through the semiconductor.

In the simplest model, it is assumed that the conduction band forms acceptor states that are energetically uniform, but it has been previously shown that there is an energetic distribution of acceptor states below the conduction band. We propose that if an electron is injected into one of these trap states that is energetically a local minimum, then it will not move and therefore block that pathway. These occupied trap states could be a limiting factor to device performance. This would then be exaggerated with the addition of Li+, as it lowers the accepter state energy levels and create deeper wells. This study will characterize the mobility of electrons by measuring the photocurrent and will investigate how Li+ intercalation3 influences these kinetics.

RESULTS AND DISCUSSION

FIGURE 1. Comparison of the photocurrent for devices with and without Li+; EG without Li+ and EGL with Li+.

FIGURE 2. Shows the effects of intermittent light on an EG device (A) and an EGL device (B). EG devices show loss of current during dark times more than EGL devices.

FIGURE 3. Displays the loss in current for an EG device before (A) and after (B) soaking for 24 hours in the dark.

FIGURE 4. Displays the minimal change in current for an EGL device before (A) and after (B) soaking for 24 hours in the dark.

REFERENCES1. O'Regan, B.; Grätzel, M. Nature 1991, 353, 737 – 740.2. Silver, M.; Pautmeier, L.; Bassler, H. Solid State Commun. 1989, 72, 177-180.3. Kopidakis, N.; Benkstein, K. D.; van de Lagemaat, L.; Frank, A. J. J. Phys. Chem.

B 2003, 107, 11307-11315.4. Make A Solar Cell- Raspberry Based. https://www.youtube.com/watch?

v=WHTbw5jy6qU(accessed Sept 02, 2014)5. Richards, F.J. Journal of Experimental Botany. 1959, 10(2), 290-300.

Miesca A. McFarland and Ian J. McNeilDepartment of Chemistry, Bridgewater College, 402 East College Street, Bridgewater, VA 22812-1599, USA

CONCLUSION

We were able to characterize the electron diffusion kinetics of DSSCs with the generalized logistic growth function. We see differences caused from the addition of lithium, but additional trials are needed to determine the significance of these differences.

METHODS4

A TiO2 nanoparticle paste is made by adding a acetic acid and dishwater soap to TiO2 nanoparticle powder. The paste is then spread onto clean ITO glass using scotch tape to control thickness and shape. It is air-dried and placed on a Bunsen burner for about an hour to sinter the film. After cooling to room temperature the film is sensitized with raspberry juice. An I-/I3

- electrolyte solution in ethylene glycol is used and LiClO4 is added to make the 1.0 M Li+ solution. A counter electrode was made by passing

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2 EG.1EG.2EG.3EG.4EG.5EG.6EG.7EG.8EGL.1EGL.2EGL.3EGL.4EGL.5EGL.6EGL.7

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Device R2 A (mA) B (sec-1)× 10-3 K (mA)EG.1 0.998 0.470 3.48 1.280EG.2 0.999 0.291 3.43 0.857EG.3 0.994 0.459 3.73 1.211EG.4 0.998 0.363 2.90 1.098EG.5 0.999 0.202 2.70 1.216EG.6 0.999 0.074 2.10 0.472EG.7 0.998 0.113 0.90 0.907EG.8 0.998 0.190 0.44 0.896

Average --- 0.270 2.46 0.992EGL.1 0.999 0.323 7.89 1.717EGL.2 0.999 0.766 0.37 2.007EGL.3 0.999 0.914 2.28 1.787EGL.4 0.999 0.030 2.36 1.230EGL.5 0.999 0.332 8.31 1.382EGL.6 0.999 0.641 7.26 1.629EGL.7 0.999 0.150 5.60 0.871

Average --- 0.451 4.87 1.517

Electron Diffusion

In order to study how electrons diffuse through the conduction band of the TiO2 nanoparticle, sixteen devices were made; eight with the electrolyte solution containing lithium (EGL) and eight with the electrolyte solution without lithium (EG). The change in current was measured for up to two hours using a digital multimeter.

Intermittent Light

A. In a similar experiment, four devices were made; two with EG and two with EGL. The light was turned on for five minutes and off for ten minutes.

B. Lastly, in an extended version of this experiment, four devices were made; two with EG and two with EGL. Each device remained exposed to light until is peaked; then the device was left in the dark overnight soaking in electrolyte solution. The device was then measured under continuous light exposure until it peaked.

Table 1. Best fit parameters from generalized logistic growth

another ITO glass slide over a candle to form a carbon soot layer. To construct the device, a few drops ofelectrolyte are sandwiched between the sensitized film and the counter electrode and held together with binder clips.

A

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