The role of the probe tip material in distinguishing p- and n-type domains in bulk heterojunction solar cells by atomic force microscopy based methods

Abstract

Visualization of functionally different domains in bulk heterojunction (BHJ) solar cells is of paramount importance to understand the routes of optimization of their structure for best performance. In this work, a concept of detecting n-type and p-type semiconductor domains in BHJ structures by methods based on atomic force microscopy (AFM) is proposed. It assigns an active role to the semiconducting coating of the AFM probe tip which is able to form different junctions, i.e., p-n anisotype or p+-p, n+-n isotype, with the surfaces inspected. Here, we illustrate this concept on the example of BHJ structures composed of the n-type inorganic microcrystalline semiconductor CdS and mechanochemically prepared p-type kesterite nanopowder and two types of AFM probe tip coatings, i.e., p-type boron-doped diamond and n-type nitrogen-doped diamond coating, respectively. Conductive AFM (CAFM) measurements demonstrated unequivocally the different diode behavior when contacting n- or p-type semiconductor domains in the BHJ structures. Simulation of the energy level alignment at the probe-sample interfaces allowed us to explain the formation of anisotype or isotype junctions depending on the sample domain and probe used. Kelvin probe force microscopy measurements were consistent with the CAFM results and indicated the different contact potentials from the diverse types of domains in the BHJ structure.

Spatially-Resolved Study of the Electronic Transport and Resistive Switching in Polycrystalline Bismuth Ferrite

“…New technology of fast data acquisition and treatment motivates to further develop CAFM for the studying of disordered and distributed systems [ 41 , 42 ]. Many efforts are taken so far to understand the current transport across the probe-sample interface [ 43 , 44 ], which is important for the correct quantitative interpretation of the local current data. Addressing the issue of the diverse influence of the microstructure in BFO films is important to control the electric transport, which in turn can help to improve the application of BFO in piezoelectric and magnetic sensors, as well as in developing an avenue of the RRAM.…”

Studies of probe tip materials by atomic force microscopy: a review

“…AFM probe tips [ 9 – 10 ] are generally fabricated with coatings, carbon nanotubes, magnetic nanoparticles, or even protein functionalization. A combination of probe resolution and durability or wear and tear and conductivity requirements must be considered before selecting a probe.…”