Thank you for the answer. I'm measuring impedance spectroscopy under 1 sun illumination using an applied voltage close to the open-circuit voltage. I'm getting smaller semicircles and as a result smaller resistances for the cell that has lower Isc. Any guesses?

Hi, 

First of all a good DSSC device should have low resistance as much as possible.

Coming to the Nquist plots, which you will get by measuring under one sun illumination conditions with open circuit voltage by applying 10mA current, voltage of 20 V and  frequency range is 1 mHz to 1MHz.

In Nqyuist plots, you will observe two semicircles generally at high frequency region and mid frequency regions. At high frequency region, there will be a small circle which corresponds to the charge transfer resistance between electrolyte and Pt electrode.

At mid frequency region, you can observe large semicircle which attributes to the internal  electron transport between TiO2/Dye and electrolyte.

If the graph has +ve voltages on Y-axis and radius of semicircle at mid frequency region is more for your interesting material than tradition one, then you can conclude that, electron recombination resistance has been increased. Hence, there is a hike in Jsc and ultimately in efficiency of device.

If you are able to fit the data by using Z-view software, then you can calculate the resistance, diffusion length and life time of electron availability. 

For further details check the below links

1. http://pubs.rsc.org/en/results?artrefjournalname=j.%20mater.%20chem.%20a&artrefstartpage=5377&artrefvolumeyear=2013&fcategory=journal

2. http://www.sciencedirect.com/science?_ob=ArticleListURL&_method=list&_ArticleListID=-622795724&_sort=r&_st=13&view=c&md5=88ed366e08b2f0ff42bb8f0faa25f22d&searchtype=a

_All the best......

_Thanks,

Chandrasekhar.

Thank you for your response. I was using a mask with an aperture area smaller than the active area of the dssc for the impedance spectroscopy measurements and I think that this was probably the reason why I was having the results that I mentioned earlier. When I repeated the impedance measurements without a mask I had smaller resistances for the dssc with the better overall efficiency.

You need not to apply mask while performing impedence measurements.