Energy level alignment in PCDTBT:PC70BM solar cells: Solution processed NiOx for improved hole collection and efficiency

Journal Article · · Organic Electronics

DOI:https://doi.org/10.1016/j.orgel.2012.01.022· OSTI ID:1065960

Ratcliff, Erin L. ^[1]; Meyer, Jens ^[2]; Steirer, K. Xerxes ^[1]; Armstrong, Neal R. ^[1]; Olson, Dana ^[3]; Kahn, Antoine ^[2]

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1. Univ. of Arizona, Tucson, AZ (United States). Dept. of Chemistry and Biochemistry
2. Princeton Univ., NJ (United States). Dept. of Electrical Engineering
3. National Renewable Energy Lab. (NREL), Golden, CO (United States). National Center for Photovoltaics

Solution-based NiO_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_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_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_x versus PEDOT:PSS interlayers.

• Research Organization: Energy Frontier Research Centers (EFRC); Center for Interface Science: Solar Electric Materials (CISSEM)
• Sponsoring Organization: USDOE SC Office of Basic Energy Sciences (SC-22)
• DOE Contract Number: SC0001084
• OSTI ID: 1065960
• Journal Information: Organic Electronics, Journal Name: Organic Electronics Journal Issue: 5 Vol. 13(5); ISSN 1566-1199
• Publisher: Elsevier
• Country of Publication: United States
• Language: English

Related Subjects

14 SOLAR ENERGY
solar (photovoltaic)
electrodes - solar
charge transport
synthesis (novel materials)
synthesis (self-assembly)
synthesis (scalable processing)