Extracting Mobility-Lifetime Product in Solar Cell Absorbers Using Quantum Efficiency Analysis

ABSTRACTThe long-wavelength quantum efficiency (QE) response of photovoltaic absorbers is determined by the length scales for minority carrier collection. However, extracting quantitative measurements of minority carrier mobility-lifetime product (μτ) is complicated by uncertainty in other factors such as the depletion width, electric field, and the absorption coefficient. We apply previously developed methods to obtain estimates for μτ in a tin(II) sulfide (SnS) solar cell. We compare three analytic models for the minority carrier collection probability as a function of absorber depth to determine which model most accurately captures the behavior in our devices. For models in which multiple parameters are unconstrained, a random numerical search is used to optimize the fit to experimental QE for SnS. To identify sources of error, we perform a sensitivity analysis by fitting with SCAPS-1D. Our analysis shows that changes in absorption most strongly affect estimates for μτ, highlighting the need to obtain accurate, device-specific absorption data. Further modeling and experimental constraints are required to obtain self-consistent values for μτ that correspond to actual device performance.

Thermally-enhanced minority carrier collection in hematite during photoelectrochemical water and sulfite oxidation

The enhancement of minority carrier mobility in hematite at elevated temperatures contributes to a substantial increase in photocurrent under illumination for oxygen evolution and sulfite oxidation reactions.

Electrical and Optical Characterisation of Silicon Nanocrystals Embedded in SiC

Silicon nanocrystals (Si NCs) are a promising candidate for the top cell of an all-Si tandem solar cell with a band gap from 1.3-1.7 eV, tuneable by adjusting NC size. They are readily produced within a Si-based dielectric matrix by precipitation from the Si excess in multilayers of alternating stoichiometric and silicon-rich layers. Here we examined the luminescence and transport of Si NCs embedded in SiC. We observed luminescence that redshifts from 2.0 to 1.5 eV with increasing nominal NC size. Upon further investigation, we found that this redshift is to a large extent due to Fabry-Pérot interference. Correction for this effect allows an analysis of the spectrum emitted from within the sample. We also produced p-i-n solar cells and found that the observed I-V curves under illumination could be well-fitted by typical thin-film solar cell models including finite series and parallel resistances, and a voltage-dependent current collection function. A minority carrier mobility-lifetime product on the order of 10-10 cm2/V was deduced, and a maximum open-circuit voltage of 370 mV achieved.

Improved Deposited Oxide Interfaces from N2 Conditioning of Bare SiC Surfaces

The benefits of a new method used to incorporate nitrogen at the dielectric/semiconductor interface of 4H-SiC oxide-based devices are presented. High temperature exposure of the SiC surface to hydrogen and nitrogen, prior to oxide deposition, greatly reduces the amount of electrically active defects to a density at least as low as the one of thermally formed interfaces. These results demonstrate the potential of increasing minority carrier mobility with a low gate dielectric forming thermal budget, with deposited dielectrics, and with limited health hazards.