Sputtered nickel oxide thin film for efficient hole transport layer in polymer-fullerene bulk-heterojunction organic solar cell

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• 作者：N. Edwin Widjonarko^a ; ^b ; ^{nicodemus.widjonarko@colorado.edu} ; Erin L. Ratcliff^c ; Craig L. Perkins^b ; Ajaya K. Sigdel^b ; ^d ; Andriy Zakutayev^b ; Paul F. Ndione^b ; Dane T. Gillaspie^b ; David S. Ginley^b ; Dana C. Olson^b ; Joseph J. Berry^b ; ^{joseph.berry@nrel.gov}
• 关键词：Nickel oxide ; Organic solar cells ; Hole transport layer ; Selective interlayer ; Work-function ; Organic-oxide interface
• 刊名：Thin Solid Films
• 出版年：2012
• 期刊代码：78_00406090
• 类别：ph
• 出版时间：1 March, 2012
• 卷：520
• 期：10
• 页码：3813-3818
• 文件大小：587 K

摘要

Bulk-heterojunction (BHJ) organic photovoltaics (OPV) are very promising thin film renewable energy conversion technologies due to low production cost by high-throughput roll-to-roll manufacturing, an expansive list of compatible materials, and flexible device fabrication. An important aspect of OPV device efficiency is good contact engineering. The use of oxide thin films for this application offers increased design flexibility and improved chemical stability. Here we present our investigation of radio frequency magnetron sputtered nickel oxide (NiO_x) deposited from oxide targets as an efficient, easily scalable hole transport layer (HTL) with variable work-function, ranging from 4.8 to 5.8 eV. Differences in HTL work-function were not found to result in statistically significant changes in open circuit voltage (V_oc) for poly(3-hexylthiophene):[6,6]-phenyl-C₆₁-butyric acid methyl ester (P3HT:PCBM) BHJ device. Ultraviolet photoemission spectroscopy (UPS) characterization of the NiO_x film and its interface with the polymer shows Fermi level alignment of the polymer with the NiO_x film. UPS of the blend also demonstrates Fermi level alignment of the organic active layer with the HTL, consistent with the lack of correlation between V_oc and HTL work-function. Instead, trends in j_sc, V_oc, and thus overall device performance are related to the surface treatment of the HTL prior to active layer deposition through changes in active layer thickness.