Kelvin Probe Force Microscopy Study of Conjugated Polymer/Fullerene Organic Solar Cells

Abstract

We conducted a comprehensive Kelvin probe force microscopy (KPFM) study of the ''classical'' organic solar cell system consisting of the MDMO-PPV:PCBM blend. The KPFM method yields detailed information of topography and local work function on the nanometer scale. Experiments were performed either in the dark or under laser illumination to extract locally resolved surface photovoltage. We identified distinct differences in energetics on the surface of chlorobenzene-and toluenecast blend films. The electronic and structural behavior of the toluene-cast blend films were analyzed in relation to illumination and substrate temperature. Together with previous studies we were able to interpret the KPFM results and draw some conclusions regarding the correlation between the nanostructural properties and photovoltaic performance of organic solar cells.

Polymer Solar Cells

“…Thereby it was further evidenced that a PFB capping layer reduced effectively the performance of the device due to its blocking of photogenerated electrons in the F8BT-rich phase from reaching the electrode. The same effect was observed earlier in polymer-fullerene blends as well [60,244]. Chiesa et al further elucidated that a simple bilayer structure is advantageous for efficient electron conduction and thus device operation [243], in accordance with Arias et al [241].…”

Scanning Kelvin Probe Microscopy on Bulk Heterojunction Polymer Blends

“…The distinct difference in phase is due to the presence (red dot) or absence (green dot) of a layer of MDMO-PPV covering the PCBM clusters. [10][11][12]14,27] This difference is also visible in the corresponding surface potential images, see Figure 1c. The covered clusters show a lower contrast in SP than the uncovered.…”

“…In principle, a quasi-continuous purely MDMO-PPV bottom layer, as was observed for toluene-cast films in Ref. [11] could form such an electron barrier. However, as will be discussed below, a similar dark0 to dark shift was observed on chlorobenzene-cast films, which do not exhibit such a bottom layer.…”

“…Recently, there has been a growing interest in using scanning Kelvin probe microscopy (SKPM) [11][12][13][14][15][16] or related techniques [17] to resolve the degree and dimensions of the phase separation in polymer bulk heterojunction solar cells. SKPM enables one to measure surface potential (SP) variations on a nanometer scale by atomic force microscopy (AFM).…”

Characteristics of Magnesium Oxide Thin Films with Co Islands Microparticulated by an Arc Plasma Gun

“…Potential distribution of the specimen, formed by depositing Co nanoparticles on a substrate using the APG with 500 pulses, was evaluated at the nanometer level by Kelvin probe force microscopy (KFM) [18][19][20][21]. From Fig.…”