In devices with intrinsic amorphous silicon layer on a crystalline silicon substrate, the light absorbed in the amorphous layer can be weakly electronically coupled into the silicon base. Such carrier injection has previously been reported from measurements on finished devices containing stacks of intrinsic and doped amorphous silicon layers. Here, we use spectral response of photoluminescence, a contactless approach, to investigate this carrier injection on significantly simpler structures. In such devices, the effect of absorption in the front layer can be measured by the internal quantum efficiency. A highly absorbing front layer is expected to cause a drop in the quantum efficiency at short wavelengths. However, if electron‐hole pairs that are generated in the front layer are subsequently injected into the base, the optical losses will be reduced, resulting in a partial recovery of the quantum efficiency at short wavelengths. Here, we quantify the efficiency of carrier injection from the intrinsic amorphous silicon front layer to the crystalline silicon base, by measuring the spectral response of photoluminescence heterojunction test structures. For devices with just an intrinsic amorphous silicon layer, the carrier injection from the layer was found to be close to unity.

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A micro‐photoluminescence‐based technique is presented, to quantify and map sheet resistances of boron‐diffused layers in silicon solar cell precursors with micron‐scale spatial resolution at room temperature. The technique utilizes bandgap narrowing effects in the heavily‐doped layers, yielding a broader photoluminescence spectrum at the long‐wavelength side compared to the spectrum emitted from lightly doped silicon. By choosing an appropriate spectral range as a metric to assess the doping density, the impacts of photon reabsorption on the analysis can be avoided; thus, an accurate characterization of the sheet resistance can be made. This metric is demonstrated to be better representative of the sheet resistance than the surface doping density or the total dopant concentration of the diffused layer. The technique is applied to quantify sheet resistances of 12‐μm‐wide diffused fingers in interdigitated back‐contact solar cell precursors and large diffused areas. The results are confirmed by both 4‐point probe and time‐of‐flight secondary‐ion mass spectrometry measurements. Finally, the practical limitations associated with extending the proposed technique into an imaging mode are presented and explained.

The spectral response of photoluminescence is a contactless method that provides a measurement of the relative external quantum efficiency of silicon solar cells and wafers. This method is accurate only if the measured luminescence originates from the radiative recombination of voltage dependent carriers. This paper investigates the impact of luminescence from voltage independent carriers in heavily diffused regions and other spurious sources of luminescence, such as luminescence from dielectric layers. A method, based on partial shading, is then demonstrated to record luminescence from only the voltage dependent carriers. This method is shown to provide accurate relative external quantum efficiency on cells and partially processed wafers. The relevance of the dependence of the measured data on the angular distribution of the incident light is demonstrated in this context, which explains errors in previously published data.