Dual Plasmonic Nanostructures for High Performance Inverted Organic Solar Cells

• DOI: 10.1002/adma.201200120
• Publication Date: 2012-05-08T09:07:20Z
• Authors: Xuanhua Li; Wallace C. H. Choy; Lijun Huo; Fengxian Xie; Wei E. I. Sha; Baofu Ding; Xia Guo; Yongfang Li; Jianhui Hou; Jingbi You; Yang Yang
• Keywords: Solar cells; Nanogratings; Polymers; Metal Nanoparticles; 02 engineering and technology; 01 natural sciences; 7. Clean energy; Nanostructures - chemistry; Plasmonic resonance; Gold - chemistry; Electric Power Supplies; Solar energy; Polymers - chemistry; Solar Energy; Organic Chemicals; Organic chemicals - chemistry; Electric power supplies; Nanostructures; 0104 chemical sciences; Metals; Nanoparticles; Fullerenes - chemistry; Metal nanoparticles - chemistry; Fullerenes; Gold; 0210 nano-technology

Polymer-fullerene-based bulk heterojunction (BHJ) solar cells have many advantages, including low-cost, low-temperature fabrication, semi-transparency, and mechanical fl exibility. [ 1 , 2 ] However, there is a mismatch between optical absorption length and charge transport scale. [ 3 , 4 ] These factors lead to recombination losses, higher series resistances, and lower fi ll factors. Attempts to optimize both the optical and electrical properties of the photoactive layer in organic solar cells (OSCs) inevitably result in a demand to develop a device architecture that can enable effi cient optical absorption in fi lms thinner than the optical absorption length. [ 5 , 6 ] Here, we report the use of two metallic nanostructures to achieve broad light absorption enhancement, increased shortcircuit current ( J sc ), and improved fi ll factor ( FF ) simultaneously based on the new small-bandgap polymer donor poly{[4,8-bis(2-ethyl-hexyl-thiophene-5-yl)-benzo[1,2-b:4,5-b ′ ]dithiophene2,6-diyl]alt -[2-(2 ′ -ethyl-hexanoyl)-thieno[3,4-b]thiophen-4,6-diyl]} (PBDTTT-C-T) in BHJ cells. [ 7 ] The dual metallic nanostructure consists of a metallic nanograting electrode as the back refl ector and metallic nanoparticles (NPs) embedded in the active layer. Consequently, we achieve the high power conversion effi ciency (PCE) of 8.79% for a single-junction BHJ OSC. Recently, plasmonic nanostructures have been introduced into solar cells for highly effi cient light harvesting. [ 5 , 8–17 ] Two types of plasmonic resonances, surface plasmonic resonances (SPRs) [ 18–22 ] and localized plasmonic resonances (LPRs), [ 11–14 ] can be used for enhancing light absorption. Metallic gratingbased light-trapping schemes have been investigated in traditional inorganic photovoltaic cells. [ 18–20 ] For metallic nanogratings, which can support SPRs, it is still challenging to experimentally demonstrate the enhancement of PCE in OSCs owing to the obvious issue of solution processing of