No abstract

This paper studies the effect of emitter width on the dc current gain, β F , and ac figures of merit, cut-off frequency, f T , and maximum oscillation frequency, f max , of realistic structures for 200 GHz SiGe heterojunction bipolar transistors (HBTs) using two-dimensional drift-diffusion (DD), hydrodynamic (HD) and energy balance (EB) simulations. The carrier transport models used are briefly presented. The SiGe-HBTs studied have a base thickness of 15 nm. Results of the three transport models are shown and analyzed, for the different emitter geometries.

No abstract

A 2D model for Cu(In,Ga)Se 2 (CIGS) solar cells under low solar concentration is described and contrasted with experimental data. Using simulation, the effect of front electric contact design parameters: finger width, finger separation, and number of buses are analyzed for solar concentrations from 1 up to 10 suns. Efficiency maps allowing front contact grid optimization are shown and analyzed for each concentration value, assessing the viability of CIGS solar cells for low concentration applications.

No abstract

Rear surface of high‐efficiency crystalline silicon solar cells is based on a combination of dielectric passivation and point‐like contacts. In this work, we develop a 3D model for these devices based on 2.2 Ωcm p‐type crystalline silicon substrates. We validate the model by comparison with experimental results allowing us to determine an optimum design for the rear pattern. Additionally, the 3D model results are compared with the ones deduced from a simpler and widely used 1D model. Although the maximum efficiency predicted by both models is approximately the same, large deviations are observed in open‐circuit voltage and fill factor. 1D simulations overestimate open‐circuit voltage because Dember and electrochemical potential drops are not taken into account. On the contrary, fill factor is underestimated because of higher ohmic losses along the base when 1D analytical model is used. These deviations are larger for relatively low‐doped substrates, as the ones used in the experimental samples reported hereby, and poor passivated contacts. As a result, 1D models could mislead to too short optimum rear contact spacing. Copyright © 2013 John Wiley & Sons, Ltd.

No abstract

Abstract:One of the most common strategies in high-efficiency crystalline silicon (c-Si) solar cells for the rear surface is the combination of a dielectric passivation with a point-like contact to the base. In such devices, the trade-off between surface passivation and ohmic losses determines the optimum distance between contacts or pitch. Given a certain pitch, the series resistance related to majority carrier flow through the base and the rear point-like contact (R base ) is commonly calculated a-priori and not crosschecked in finished devices, since typical techniques to measure series resistance lead to an unique value that includes all ohmic losses. In this work, we present a novel method to measure R base using impedance spectroscopy (IS) analysis. The IS data at high frequencies allow to determine R base due to the presence of the capacitor formed by the metal/dielectric/semiconductor structure that covers most of the rear surface. The method is validated by device simulations where the dependence of R base on carrier injection, base resistivity and pitch are reproduced. Finally, R base is measured on finished devices. As a result, a more accurate value of the contacted area is deduced which is a valuable information for further device optimization.