Energy Level Alignment in PCDTBT:PC70BM Solar Cells: Solution Processed NiOx for Improved Hole Collection and Efficiency

Journal Article · Tue May 01 04:00:00 EDT 2012 · Organic Electronics

DOI:https://doi.org/10.1016/j.orgel.2012.01.022· OSTI ID:1040949

Ratcliff, Erin L.; Meyer, Jens; Steirer, K. Xerxes; Armstrong, Neal R.; Olson, Dana; Kahn, Antoine

Solution-based NiO{sub x} outperforms PEDOT:PSS in device performance and stability when used as a hole-collection layer in bulk-heterojunction (BHJ) solar cells formed with poly[N-9'-heptadecanyl-2,7-carbazole-alt-5,5-(4',7'-di-2-thienyl-2',1',3'-benzothiadiazole)] (PCDTBT) and PC70BM. The origin of the enhancement is clarified by studying the interfacial energy level alignment between PCDTBT or the 1:4 blended heterojunctions and PEDOT:PSS or NiO{sub x} using ultraviolet and inverse photoemission spectroscopies. The 1.6 eV electronic gap of PEDOT:PSS and energy level alignment with the BHJ result in poor hole selectivity of PEDOT:PSS and allows electron recombination at the PEDOT:PSS/BHJ interface. Conversely, the large band gap (3.7 eV) of NiO{sub x} and interfacial dipole (0.6 eV) with the organic active layer leads to a hole-selective interface. This interfacial dipole yields enhanced electron blocking properties by increasing the barrier to electron injection. The presence of such a strong dipole is predicted to further promote hole collection from the organic layer into the oxide, resulting in increased fill factor and short circuit current. An overall decrease in recombination is manifested in an increase in open circuit voltage and power conversion efficiency of the device on NiO{sub x} versus PEDOT:PSS interlayers.

• Research Organization: National Renewable Energy Laboratory (NREL), Golden, CO (United States)
• Sponsoring Organization: USDOE Office of Energy Efficiency and Renewable Energy (EERE), Solar Energy Technologies Office (EE-4S)
• DOE Contract Number: AC36-08GO28308
• OSTI ID: 1040949
• Report Number(s): NREL/JA-5200-54756
• Journal Information: Organic Electronics, Journal Name: Organic Electronics Journal Issue: 5 Vol. 13
• Country of Publication: United States
• Language: English

Related Subjects

14 SOLAR ENERGY
ALIGNMENT
DIPOLES
EFFICIENCY
ELECTRIC POTENTIAL
ELECTRICAL FAULTS
ELECTRONIC STRUCTURE
ELECTRONS
ENERGY LEVELS
FILL FACTORS
HETEROJUNCTIONS
ORIGIN
PCDTBT
PERFORMANCE
PHOTOEMISSION
RECOMBINATION
SOLAR CELLS
SPECTROSCOPY
STABILITY
blend
electronic structure
interface dipole
photoemission spectroscopy