Low Molecular Mass Organogelators As Additives in Liquid Electrolyte Dye Sensitized Solar Cells
Authors: Sarwar Saad , Hong Sungjun , Han Chi-Hwan 
Published: February 2020

Background/ Objectives and Goals

Dye sensitized solar cells (DSSCs) have grabbed a lot of attention in both academic and industrial sector since the pioneering work of Michael Gratzel owing to the easy fabrication, low material cost, and relatively high power conversion efficiency as well as the easy adoption to Building Integrated Photovoltaic (BIPV). However, long term stability is one of the most vital factors and is the major hurdle in the way of commercializing DSSCs. The origins of DSSC’s instability have been proposed to originate from various factors including leakage of electrolyte at high temperature, dye degradation or detachment from TiO2 surface and loss of iodine. Gel type electrolyte has been used in DSSCs to inhibit solvent leakage and evaporation which is inevitable in the case of liquid electrolytes. Low molecular mass organogelators (LMOGs) are good candidate among the gel type electrolytes because of their porous nature and tunable properties. These types of gels are proven to be quite stable and can hold the content in them preventing it from leakage.

Methods

To make the LMOG, first Lauroyle Chloride (0.14 mol) was added to a stirred solution of NaHCO3 (0.13 mol) in Ether (150 ml) and DI water (150 ml) at 0 °C. The temperature was maintained using an ice bath. Then Diamino cyclohexane (0.044 mol) was added in the above solution drop by drop. The solution was kept at 0 °C. After that the solution was stirred at room temperature for 8 hours. The resulting solid was filtered and washed with DI water three times and dried in oven at 70 °C. The solid was recrystallized using Ethanol (~250 ml) and filtered and dried again. The resultant was very fine needle like crystals
To make the gel type electrolyte, 1.5, 3.0 and 4.5 wt% LMOG was mixed with the ESK electrolyte and heated at 110 °C until the LMOG melted and solution became homogeneous. Hot electrolyte was introduced into preheated cells (80 °C) to prevent the gelation upon contact with cells. The vial containing electrolyte with mixed LMOG, was let cool down at room temperature to perform the gelation. Gelation was checked by inverting the vial and checking the gel against gravity.

Expected Results/ Conclusion/ Contribution

The successful formation of LMOG was checked by H-NMR which confirmed the structure of proposed LMOG. The prepared LMOG worked very well to gelate the liquid electrolyte. Even a very small amount i.e. 1.5 wt % was enough to gelate the electrolyte. The small amount of gelator functions well and does not interfere with the performance of the electrolyte. A big advantage of this electrolyte system is that it is liquid when introduced to the cells, which is conventional unlike other gel electrolyte systems where the gel is formed before applying to the DSSC and electrolyte does not wet the photoanode properly.
The performance of the cells was measured under 1-sun Solar Simulator (Abet Technologies). The efficiency of the cells was par and in some cases even better than the cells with liquid electrolyte. The summary of the performance can be seen in the following table.

Sample

Jsc

Voc

FF

Efficiency

ESK

10.25
0.77
0.57
4.49 +- 0.66

1.5wt%

10.58
0.74
0.64
5.04 +- 0.23

3.0wt%

10.70
0.75
0.64
5.09 +- 0.38

4.5wt%

10.30
0.72
0.52
3.91 +- 0.77

A long term stability study at elevated temperature (60 °C) is underway currently.