Porous multi junction thin-film silicon solar cells for scalable solar water splitting

© 2018 Elsevier B.V. Monolithic solar water splitting devices implemented in an integrated design approach, i.e. submerged in the electrolyte, pose a significant limitation when it comes to up-scaling. The ion transport distances around the monolith are long and consequently, the ionic Ohmic losses become high. This fact turns out to be a bottleneck for reaching high device efficiency and maintaining optimum performance upon up-scaling. In this paper, we propose a new device design for integrated monolithic solar water splitting based on porous multi-junction silicon solar cells. Simulation results highlight that porous monoliths can benefit from lower ionic Ohmic losses compared to dense monoliths for various pore geometries and monolith thicknesses. In particular, we show how micrometer scale pore dimensions could greatly reduce Ohmic losses, thereby minimizing overpotentials. A square array of holes with a diameter of 20 µm and a period of 100 µm was fabricated on single-junction and multi-junction amorphous and microcrystalline silicon solar cells. A small impact on the open circuit voltage (Voc) and short circuit current density (Jsc) was obtained, with porous triple junction solar cells reaching Voc values up to 1.98 V. A novel device design is proposed based on porous triple-junction silicon-based solar cells.status: publishe

Quantification of Valleys of Randomly Textured Substrates as a Function of Opening Angle: Correlation to the Defect Density in Intrinsic nc-Si:H

Optical and electrical properties of hydrogenated nanocrystalline silicon (nc-Si:H) solar cells are strongly influenced by the morphology of underlying substrates. By texturing the substrates, the photogenerated current of nc-Si:H solar cells can increase due to enhanced light scattering. These textured substrates are, however, often incompatible with defect-less nc-Si:H growth resulting in lower Vo. and FF. In this study we investigate the correlation between the substrate morphology, the nc-Si:H solar-cell performance, and the defect density in the intrinsic layer of the solar cells (i-nc-Si:H). Statistical surface parameters representing the substrate morphology do not show a strong correlation with the solar-cell parameters. Thus, we first quantify the line density of potentially defective valleys of randomly textured ZnO substrates where the opening angle is smaller than 130 degrees (rho(<130)). This rho(<130) is subsequently compared with the solar-cell performance and the defect density of i-nc-Si:H (rho(defect)), which is obtained by fitting external photovoltaic parameters from experimental results and simulations. We confirm that when rho(<130) increases the V-oc and FF significantly drops. It is also observed that rho(defect) increases following a power law dependence of rho(<130). This result is attributed to more frequently formed defective regions for substrates having higher rho(<130)

2-D Periodic and Random-on-Periodic Front Textures for Tandem Thin-Film Silicon Solar Cells

We evaluate the performance of thin-film silicon micromorph tandem solar cells deposited on transparent superstrates with embossed micrometer-scale 2-D gratings. Once coated with a thin conductive layer of hydrogenated indium oxide, the textured superstrates can be used as 2-D periodic single-texture front electrodes. Combining these almost loss-free front electrodes with a highly transparent, random self-textured zinc oxide layer (with a thickness 1 um) deposited by low-pressure chemical vapor deposition (LPCVD), we obtain double-texture transparent front electrodes. The potential of both single- and double-texture front electrodes is estimated by varying the illumination spectrum of the solar simulator, thereby assessing the maximum efficiency of the tandem cells under optimal current-matching conditions. Our results demonstrate the complementary roles of the 2-D gratings and the LPCVD-ZnO layers in double textures: Cell efficiencies as high as with our state-of-the-art 2.3-um-thick LPCVD-ZnO front electrode are obtained with significantly reduced ZnO layer thicknesses. Additionally, we show that equivalent efficiencies are also within reach with 2-D periodic single textures if the proper cell configuration is applied

Light harvesting schemes for high efficiency thin film silicon solar cells

Objectives Patient recall of medical information is usually poor. Healthcare providers can employ affect-oriented (i.e., showing care) or cognition-oriented communication styles (i.e., structuring information) to enhance recall, but research evidence is limited especially among clinical and/or older patient populations. This video-vignette study manipulated provider caring and information structuring to examine effects on recall and trust among cancer patients/survivors. Methods In an online survey, 148 participants (Mage = 62) were randomized to one of four video conditions in a two (standard communication vs. enhanced caring) by two (standard vs. enhanced structuring) design, and completed measures of active recall, recognition, and trust. Results Increased caring or structuring did not enhance active recall or recognition, instead both were higher among younger, female, or highly educated participants. The caring condition induced higher perceived trust in the provider within the whole sample, but trust was significantly correlated with decreased recall (r = −.268) among younger participants. Conclusions Provider caring can strengthen the patient-provider relationship by enhancing trust. Yet, increased trust may impair recall among younger patients. Structuring treatment information did not enhance recall and recognition, but additional research is needed. Practice implications Providers may use additional ways of structuring/organizing information to help enhance recall (e.g., written information)