Imaging the Electric Potential within Organic Solar Cells

Abstract

The charge transport in organic solar cells is investigated by surface potential measurements via scanning Kelvin probe microscopy. Access to the solar cell's cross‐section is gained by milling holes with a focused ion beam which enables the direct scan along the charge transport path. In a study of poly(3‐hexylthiophene):1‐(3‐methoxycarbonyl)propyl‐1‐phenyl[6,6]C61 (P3HT:PCBM) bulk heterojunction solar cells, the open circuit voltage is built up at the top contact. A comparison of the potential distribution within normal and inverted solar cells under operation exhibits strongly different behaviors, which can be assigned to a difference in interface properties.

Sample preparation for scanning Kelvin probe microscopy studies on cross sections of organic solar cells

“…With the presented methods we investigated OSC cross sections under bias voltages too (presented in Saive et al). 17 The high degree of agreement between the SKPM results proves that with all of the three presented methods it is possible to prepare samples that are suitable for meaningful SKPM studies. The modification of the surface's electrical properties through contamination in ambient air or the FIB treatment seems not to have a significant influence on the SKPM results.…”

“…The same results were obtained also for samples from the other preparation methods (data from FIB milled samples published in Saive et al). 17 In a further analysis (not presented here) we were able to prove that this photovoltage drops at the BHJ-Al/LiF interface only, no matter if the top cathode or the bottom anode was floating. 17 Also these results could be reproduced in all of the measurements and on samples from all of the three preparation methods.…”

“…17 In a further analysis (not presented here) we were able to prove that this photovoltage drops at the BHJ-Al/LiF interface only, no matter if the top cathode or the bottom anode was floating. 17 Also these results could be reproduced in all of the measurements and on samples from all of the three preparation methods. With the presented methods we investigated OSC cross sections under bias voltages too (presented in Saive et al).…”

Functional Scanning Force Microscopy for Energy Nanodevices

“…The field‐free region inside BHJ expanded when TiO x was incorporated as cathode interlayer, confirming that the electric field was confined at the cathode interface . Saive et al used FIB to cut both conventional and inverted structure OPV devices, and measured cross‐sectional potential distribution by using UHV‐SKPM . The potential profiles of conventional structure in dark and under illumination in open‐circuit condition were shown, and the difference was interpreted as building‐up of photovoltage.…”

Nondestructive Method for Mapping Metal Contact Diffusion in In2O3 Thin-Film Transistors

“…2−5 Using the known tip work function, a 2D map of the sample surface work function can then be reconstructed. 1−3 Measurements of the surface potential on operating transistors are complicated by mobile charges which are continuously created and transported across the device 6 and are influenced by the external field of the measuring probes.…”