In this writing, in order to understand stability/degradation in organic solar cell devices, the device stability of poly(3-hexylthiophene) P3HT and poly(benzo[1,2-b:4,5-b' ]dithiophenealt- terthiophene (BDT-3T) is discussed. The OPVs were fabricated using the polymers and [6,6]-phenyl-C61-butyricacidmethylester (PC[60]BM) as donor and acceptor, respectively. The effect of O2 on device stability was examined by keeping the P3HT and BDT-3Tdevices in N2 and airand the humidity was controlled by introducing getter on encapsulation of device. The experiment was done until thousands of hours. The device stabilityof new copolymer BDT-3T was comparable to that of P3HT.