Stability study of low and high band gap polymer and air stability of PTB7:PC71BM bulk heterojunction organic photovoltaic cells with encapsulation technique

• Study air stability of low and high band gap polymers in organic photovoltaic devices.
• Effect of TiOx layer on the stability of low and high band gap polymers in organic photovoltaic devices.
• Degradation prevention of low band gap polymer in organic photovoltaic devices by encapsulation technique.

This study describes the air stability of organic photovoltaic (OPV) cells based on low band gap polymer, thieno(3,4-b)-thiophene/benzodithiophene copolymer and [6,6]-phenyl C71 butyric acid methyl ester (PTB7:PC71BM) bulk heterojunction (BHJ) with titanium oxide (TiOx) layer. The ITO/PEDOT:PSS/PTB7:PC71BM/TiOx/Al device was fabricated and protected via an encapsulation technique. An optical sealant glass was used for encapsulating the device. We succeeded to keep the device in air for 20 days without a significant loss of its initial power conversion efficiency (PCE). After 20 days, the PTB7:PC71BM/TiOx device without encapsulation in air showed a rapid decrease in power conversion efficiency (PCE), losing approximately more than 98.0% of its initial value. The efficiency decays of the encapsulated devices in the nitrogen filled glove box and in air were about 32.3% and 41.7%, respectively. The organic photovoltaic cells based on high band gap polymer, poly(3-hexylthiophene) and [6,6]-phenyl C71 butyric acid methyl ester (P3HT:PC71BM) BHJ with TiOx layer was fabricated. We compared the stability of P3HT:PC71BM and PTB7:PC71BM OPV devices for 10 days in a glove box with and without TiOx layer. We found that the device based on PTB7:PC71BM/TiOx organic photovoltaic cell has better stability than the P3HT:PC71BM/TiOx organic photovoltaic cell.