A Study on Axially Graded Si_(1-x)Ge_(x) Nanowire Solar Cell with Monte Carlo Simulation

This paper presents a study on the performance of an axially graded Ge-Si<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">(1-x)</inf>Ge<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</inf>-Si p-n nanowire solar cell using Monte Carlo simulation. The nanowire structure consists of a germanium (Ge) cathode, silicon (Si) anode, and a variable Si<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">(1-x)</inf>Ge<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</inf> middle region. The Silvaco code incorporates quantum mechanical effects such as Fermi statistics for carrier distribution, SRH recombination for trap-assisted processes and non-equilibrium transport using the Bi-Conjugate Gradient method. The study focuses on key photovoltaic parameters, including short-circuit current density (Jsc), open-circuit voltage (Voc), maximum power (Pm), and fill factor (FF), to assess the solar cell's efficiency. Through extensive simulations with different x compositions in the middle region, it is found that the Ge-Ge-Si<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.5</inf>Ge<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.5</inf>-Si structure delivers the best results, offering enhanced photovoltaic performance. We also conducted a comparison of the three different solar cell structures: (a) Ge-Si(0.5)Ge<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.5</inf>-Si, (b) axially graded Ge-Si<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.1</inf>Ge<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.9</inf>-Si<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.5</inf>Ge<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.5</inf>-Si<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.9</inf>Ge<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.l</inf>-Si, and (c) core-to-shell graded Ge-Si<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">(1-x)</inf>Ge<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</inf>-Si. These findings provide insights into the optimal design of graded nanowire solar cells for improved efficiency.