Department of Physics, Engineering Physics & Astronomy

Department of Physics, Engineering Physics & Astronomy
Department of Physics, Engineering Physics & Astronomy

Enhanced Photovoltaic Conversion Efficiency in Bulk Heterojunction Solar Cells by Materials and Device Architecture Engineering

Ricardo Izquierdo
Departement d'Informatique, University of Québec, Montréal

Date: Friday, January 25, 2013
Time: 1:30 PM
Location: Stirling A


Polymer solar cells are emerging as an alternative inexpensive renewable source of green energy due to their interesting properties, such as, low-temperature based manufacturing, mechanical flexibility and solution processability. However, efficiency still to be improved in order to make a viable technology. Here we report on various approaches to increase the efficiency by engineering the materials or the device architecture. First, a modified bulk heterojunction (BHJ) solar cell in which a nanohybrid composite material made of lead sulfide (PbS) colloidal quantum dots (QDs) and multiwall carbon nanotubes (MWCNTs) was incorporated onto a standard regioregular poly(3-hexylthiophene) (rr-P3HT):phenyl-C61-butyric acid methyl ester (PCBM) blend. This hybrid device exhibits a higher power conversion efficiency (PCE) of ~3.40% as compared to that of ~2.57% for a control rr-P3HT:PCBM BHJ solar cell made under the same experimental conditions. The increase in efficiency by 33% is mainly attributed to the extended quantum-dot-sensitization in the nearest infrared (NIR) due to the absorbance of PbS-QDs/MWCNTs in the spectral range from 700 nm to 1500 nm. In a second approach, engineering of both electrode interfaces through the introduction of ultra thin layers of donor- and acceptor- type materials at the anode/BHJ and BHJ/cathode interfaces, was done. The introduction of the P3HT and modified C60 at the anode and cathode interfaces improve the hole and electron extraction from the BHJ layer to either electrode. From the experimental observations, we presume that upon interposing such interfacial layers at the anode/BHJ and BHJ/cathode interfaces could repair poor contact at the anode/hole-donor and electron-acceptor/cathode interfaces and prevent undesired vertical phase segregation. The PV cell fabricated from poly(3-hexylthiophene) (P3HT) as donor and C55H36O as acceptor, exhibit an optimal power conversion efficiency (PCE) of 4.14%, where when C72H16S is used a highest PCE of 4.35% was observed.