We will present nano-scale correlation of structural, electronic and optical properties of GaN-based power devices by cathodoluminescence directly performed in a scanning transmission electron microscope. The two-dimensional electron gas (2DEG) of a lateral AlGaN/GaN field-effect transistor has been investigated directly probing the local origin of the 2DEG by its spectral luminescence fingerprint. This characteristic 2DEG luminescence is locally observed nanometers inside the GaN - close to the GaN/AlN/AlGaN interface. Furthermore, a lateral p-n+ superjunction will be presented, where excitonic and donor-acceptor transitions directly visualize the space charge region evidencing the exciton dissociation in the built-in electric field.
In the last years, hybrid organic/inorganic solar cells have attracted great interest in photovoltaic research due to their expected potential to combine the advantages of both material classes, the excellent electrical properties and stability of the inorganic and the low-cost processability of the organic semiconductors. This work is focused on hybrid solar cells based on n-doped crystalline Si as the inorganic and the polymer poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) as the organic part of the device. The hole-conducting organic semiconductors poly(3-hexylthiophene-2,5-diyl) (P3HT) and 2,2′,7,7′-Tetrakis[N,N-di(4-methoxyphenyl)amino]-9,9′-spirobifluorene (Spiro-MeOTAD) are investigated as electron blocking interlayers to reduce the parasitic electron current into the metal top contact and thereby increase the efficiency of the solar cell. In this context, P3HT is identified to be insufficient as an interlayer material due to unfavorable hysteresis effects. On the other hand, for solar cells with a Spiro-MeOTAD interlayer, the power conversion efficiency (PCE) is significantly increased. This is mainly attributed to an increased short-circuit current density. For the best performing device, a PCE of 14.3% is achieved, which is one of the highest values reported for this type of hybrid solar cells so far.