Applying a proper trendline.

I have to apply a correct trendline to a given set of data. I've attached the excel workbook below. It's the sheet called 'T1 vs. t'. I have to apply a trendline to this data. From the looks of it, it's some sort of exponential decay. However, when I apply an exponential trendline to this data, it just applies a linear line through the data. How can I choose a trendline which actually fits this data?