Resolving the Impact of Structural Defects on the Charge Carrier Transport in (Opto)electronics

Extended structural defects, like grain or domain boundaries in polycrystalline semiconductors, can introduce mid-bandgap trap states, host dopants or lead to electrostatic barriers. The implications of these local defects for charge carriers in materials used for (opto)electronic applications can be manifold: They can act as non-radiative recombination centers, delay or restrict the charge transport or, in some cases, improve the transport properties though a change in doping.<br/>Here, we will discuss how electrical and electromechanical atomic force microscopy (AFM) in combination with complimentary techniques can not only resolve extended defects, but also capture their electronic or (electro)mechanical properties and relate these defects to local changes in charge carrier transport. For instance, using electromechanical AFM, we visualized subcrystalline twin domains present in hybrid organic inorganic perovskites that are applied in photovoltaic devices. With the data analysis exacerbated by the mixed ionic and electronic conductivity of hybrid perovskites, we conducted advanced electromechanical AFM to decouple mechanical and electrostatic crosstalk, which finally revealed the ferroelastic nature of the domains. Correlating to spatial- and time-resolved photoluminescence suggest that the domain walls as extended structural defects delay the charge carrier diffusion by acting as electrostatic barriers. However, the possibility to tailor the arrangement and density of these ferroelastic domains allows engineering a directional charge transport and improved device performance.