Inverted Polymer Solar Cells

Inverted bulk heterojunction polymer solar cells have become the preferred device architecture for roll-to-roll (R2R) processing, which allows large area devices to be fabricated on flexible substrates. Significant improvements in inverted solar cell performance have been made with novel photovoltaic polymers, along with optimized blend morphology and improved carrier extraction materials. For the first time, inverted polymer solar cells display their potential for low-cost R2R processing with power conversion efficiencies exceeding 8%

Dithienogermole As a Fused Electron Donor in Bulk Heterojunction Solar Cells

We report the synthesis and bulk heterojunction photovoltaic performance of the first dithienogermole (DTG)-containing conjugated polymer. Stille polycondensation of a distannyl-DTG derivative with 1,3-dibromo-N-octyl-thienopyrrolodione (TPD) results in an alternating copolymer which displays light absorption extending to 735 nm, and a higher HOMO level than the analogous copolymer containing the commonly utilized dithienosilole (DTS) heterocycle. When polyDTG-TPD:PC70BM blends are utilized in inverted bulk heterojunction solar cells, the cells display average power conversion efficiencies of 7.3%, compared to 6.6% for the DTS-containing cells prepared in parallel under identical conditions. The performance enhancement is a result of a higher short-circuit current and fill factor in the DTG-containing cells, which comes at the cost of a slightly lower open circuit voltage than for the DTS-based cells