BACKGROUND:  Conjugated polymers are useful for a variety of electronic applications. In the past few years, photovoltaic devices based on conjugated polymers have been extensively studied. The most widely used configuration of polymer solar cells is the so-called "bulk heterojunction" devices in which the active layer consists of a blend of an electron-donating materials, e.g., a p-type conjugated polymer, and an electron-accepting (n-type) material such as (6,6)-phenyl C61-butyric acid methyl ester (PCBM). Regioregular poly(3-alkylthiophene)s (P3ATs) have been found to be one of the most promising conjugated polymers. Further improvement in power conversion efficiency (PCE) entails new conjugated polymers with higher carrier mobility and broader absorption of the solar spectrum, especially in the red and infrared range.

INNOVATION:  The innovation involves the synthesis and characterization of optical and electrochemical properties of a regioregular copolymer, poly(3-octylthiophene-2,5-diyl-co-3-decyloxythiophene-2,5-diyl) (POT-co-DOT), and an alternating regioregular copolymer poly{(9,9-dioctylfluorene)-2,7-diyl-alt-[4,7-bis(3-decyloxythien-2-yl)-2,1,3-benzothiadiazole]-5',5"-diyl} (PF-co-DTB). The incorporation of 3-alkoxythiophene units onto the conjugated backbones enhances the electron-donating property of the polymer and lowers its bandgap. The fabrication and performance of photovoltaic cells with bulk heterojunction architecture based on blends of these copolymers with PCBM are also described.

POTENTIAL APPLICATIONS 

• Organic solar cells
• Polymer thin film transistors
• Polymer memory devices
• Polymer LEDs
• Light emitting electrochemical cells
• Electrochromic devices

DEVELOPMENT-TO-DATE:  Performance of bulk hetero-junction solar cells fabricated using blends of these polymers with PCBM was measured under white light illumination (AM 1.5 G, 100 mW/cm2), the obtained short circuit current density (Jsc) was 6.3 mA/cm2, open circuit voltage (Voc) was 0.76V, fill factor (FF) was 50.5%, and PCE was 2.4 %. Study to further improve the solar cell architecture and power conversion efficiency is underway.

Reference: UCLA Case No. 2006-494

PCT Application: WO/2007/109545