Amirjan Nawabjan

Junction Formation With HWCVD and TCAD Model of an Epitaxial Back-Contact Solar Cell

In this paper, we present morphological and electrical characteristics of a junction formed of Si p-type films deposited on an n-type silicon wafer using a hot wire chemical vapor deposition (HWCVD) tool. We describe the fabrication process and study the influence of diborane flow and postprocess annealing in improving junction characteristics. Our morphological studies undertaken using atomic force microscopy show that the initial deposition suffered from voids rather than being a uniform film; however, this improves significantly under our annealing treatment. The improvement in morphology was observed in the electrical characteristics, with estimated Voc doubling and rectification of the junction improving by several orders of magnitude. Fitting of the current-voltage curves to a two-diode model showed that increasing the diborane flow in the process helps reduce the saturation current and ideality factors, while increasing the shunt resistance. Electrochemical capacitance-voltage (ECV) and quasi-steady-state photoconductance measurements are used to characterize the deposited films further. A solar cell device with a silicon epitaxy emitter is modeled using industry-standard 3-D modeling tools and input parameters from experimental data, and the impact of defects is studied. A potential efficiency approaching 25% is shown to be feasible for an optimized device.

Epitaxial Interdigitated Back Contact (IBC) solar cell test platform for novel light trapping schemes

An Interdigitated Back Contact (IBC) solar cell is being developed for evaluation of emerging light trapping schemes of silicon nanowire arrays on pyramidal textured surfaces. The front surface of the baseline IBC cell design was optimized with a thin film coating considering both antireflection and passivation to reduce surface recombination. Addition of a front surface field (FSF) was shown to improve the surface passivation of the cell. PC2D simulations of the baseline device predict an efficiency of 17.4%. Silicon nanowire arrays and hybrid structures of silicon nanowires on pyramids were successfully fabricated. Hemispherical reflectance measurements show that a weighted average reflectance of just 1.89% was achieved. With adequate surface passivation, these highly-effective antireflective structures could result in a power conversion efficiency increase compared to traditional light trapping methods when incorporated into the IBC cell.