Implications of TCO Topography on Intermediate Reflector Design for a-Si/μc-Si Tandem Solar Cells—Experiments and Rigorous Optical Simulations

Abstract

The influence of the transparent conducting oxide (TCO) topography was studied on the performance of a silicon oxide intermediate reflector layer (IRL) in a-Si/μc-Si tandem cells, both experimentally and by 3-D optical simulations. Therefore, cells with varying IRL thickness were deposited on three different types of TCOs. Clear differences were observed regarding the performance of the IRL as well as its ideal thickness, both experimentally and in the simulations. Optical modeling suggests that a small autocorrelation length is essential for a good performance. Design rules for both the TCO topography and the IRL thickness can be derived from this interplay. Index Terms-3-D rigorous optical modeling, a-Si/μc-Si, intermediate reflector, micromorph, solar cells, transparent conducting oxide (TCO). I. INTRODUCTION AND BACKGROUND A S THE demand for affordable clean energy grows, amorphous silicon (a-Si) / microcrystalline silicon (μc-Si) tandem solar cells are an interesting technology, as it combines nontoxic and abundant materials with a low temperature/low cost process. However, the conversion efficiency of these de-Manuscript

Resolving the nanostructure of plasma-enhanced chemical vapor deposited nanocrystalline SiOx layers for application in solar cells

“…During the past years, hydrogenated nanocrystalline silicon oxide (nc-SiO x :H) fabricated by plasma enhanced chemical vapor deposition (PECVD) has been developed as a versatile material for use in silicon based solar cells, e.g., as an intermediate reflective layer (silicon oxide intermediate reflector, SOIR) in amorphous-silicon (aSi:H)/microcrystalline-silicon (lc-Si:H) tandem solar cells that increases light harvesting in the a-Si:H top cell. [1][2][3] Since the electrical and optical parameters of the material are tunable within a wide range, 4 several other applications for solar cells have been explored. The material has been used as a transparent n-type 5 or p-type contact for heterojunction, 6,7 and thin-film silicon solar cells [8][9][10][11] or as a dielectric layer in back reflectors for a thin film single-junction 12 or doublejunction solar cells.…”

Light-management potential of dual-function n-SiO in the top junction of micromorph solar cells with different front electrodes

“…With the other textures, characterized by the presence of smaller features, an index grading effect is instead present at the a-Si:H/n-SiO x interface that partially reduces the back reflection of light toward the top cell. In other terms the different performance depends on the variation of the normal component of the wave vector -which is the relevant component for the intermediate reflector functioning mechanisms -with changes in the scattering properties of the TCOs [19]. It is also interesting to notice that with s-SE and m-SE ZnO there is practically no dependence of EQE top on n-SiO x thickness in the present range, while with LPCVD ZnO there is a gradual increase of J sc-top with thicker layers.…”

“…To mitigate this issue, inter-reflection layers have been proposed to partially reflect the incident light back into the top cell, hence allowing for a reduction of the top cell thickness [16]. Materials with refractive index lower than silicon, like doped ZnO and n-type mixed-phase silicon-rich silicon oxide (n-SiO x ) have been investigated as appropriate reflectors [9,[16][17][18][19][20]. The latter, with almost independently tunable optical and electrical properties, can be even optimized for use as an n-type layer in the p-i-n subcells.…”

“…Here we have extended the concept to more efficient substrates characterized by different scattering properties in order to fully explore the potential of this simple and cost-competitive approach in light-management perspectives. It is in fact known that the roughness of the TCO has an influence on the performance of intermediate reflectors [19,20]. Likewise, the optical effects of the dual-function n-layer are expected to depend on the front electrode morphology.…”

Balance of optical, structural, and electrical properties of textured liquid phase crystallized Si solar cells

“…Here, the respective PDMS mold was fabricated using a commercially available textured ZnO:Al layer on glass (master structure), which had been deposited by magnetron sputtering and textured by hydrochloric acid. 10 The master structure exhibited a R rms of 125 nm. The large differences of the FIG.…”