P3HT-b-PS Copolymers as P3HT/PCBM Interfacial Compatibilizers for High Efficiency Photovoltaics

Journal Article · Sat Jan 01 00:00:00 EST 2011 · Advanced Materials

DOI:https://doi.org/10.1002/adma.201103361· OSTI ID:1031007

Sun, Zhenzhong ^[1]; Xiao, Kai ^[1]; Yu, Xiang ^[1]; Hong, Kunlun ^[1]; Keum, Jong Kahk ^[1]; Browning, Jim ^[1]; Ivanov, Ilia N ^[1]; Chen, Jihua ^[1]; Alonzo Calderon, Jose E ^[1]; Sumpter, Bobby G ^[1]; Payzant, E Andrew ^[1]; Rouleau, Christopher M ^[1]; Geohegan, David B ^[1]

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1. ORNL

To control the donor-acceptor phase separation for more efficient organic bulk heterojunction photovoltaic cells, poly(3-hexylthiophene)-block-polystyrene (P3HT-b-PS) diblock copolymer was added to serve as a compatibilizer in a P3HT/ [6,6]-phenyl-C61-butyric acid methyl ester fullerene derivative (PCBM) blend. An addition of 5 wt% of P3HT-b-PS copolymer in the P3HT/PCBM blend improved the power-conversion efficiency from 3.3% to 4.1% due to an enhancement of both the short-circuit current density and fill factor compared to that of a pristine P3HT/PCBM solar cell. Grazing incidence x-ray scattering (GIXS), absorption spectroscopy and carrier mobility studies reveal that the crystallinity and orientation of P3HT were improved, thereby enhancing hole transport in the P3HT polymer, and leading to a better balance between the electron and hole mobilities in the P3HT/PCBM active layer. Neutron reflectometry (NR) experiments demonstrate that a distinct scattering length density profile shows the highest PCBM concentration in the middle layer region and a more compact and homogeneous layer, presumably due to an increase in miscibility of P3HT and PCBM driven by the copolymer compatibilizer, while adding 5 wt% of P3HT-b-PS copolymer in the P3HT/PCBM blend. Quantum density functional theory calculations show that the P3HT-b-PS additive tends to promote microphase segregation, with the PCBM attracted to the PS block, and the P3HT stacking onto the P3HT block, which presumably leads to improvements in long-range crystallinity , consistent with the GIXS findings. Overall, the results for P3HT-b-PS copolymer in a P3HT/PCBM blend demonstrate that tailored block copolymers can act as an effective compatibilizer in blended systems to further improve solar cell performance

• Research Organization: Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Center for Nanophase Materials Sciences (CNMS); Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Spallation Neutron Source (SNS)
• Sponsoring Organization: USDOE Office of Science (SC)
• DOE Contract Number: DE-AC05-00OR22725
• OSTI ID: 1031007
• Journal Information: Advanced Materials, Vol. 23, Issue 46; ISSN 0935-9648
• Country of Publication: United States
• Language: English

Related Subjects

14 SOLAR ENERGY
ABSORPTION SPECTROSCOPY
ADDITIVES
CARRIER MOBILITY
COPOLYMERS
CURRENT DENSITY
EFFICIENCY
ELECTRONS
ESTERS
FILL FACTORS
FULLERENES
FUNCTIONALS
HETEROJUNCTIONS
NEUTRONS
ORIENTATION
PHOTOVOLTAIC CELLS
SCATTERING
SCATTERING LENGTHS
SEGREGATION
SOLAR CELLS
SOLUBILITY