Simulation of a-Si:H dual junction solar cells

Abstract

In this paper the behaviour of the current density-voltage (J-V) characteristic curves of hydrogenated amorphous silicon (a-Si:H) tandem solar cells (a-Si:H/a-Si:H) with heavy doped tunnelling junction of hydrogenated microcrystalline silicon (JLc-Si:H) n±/p± is analysed. The multi-junction solar cells are being used as an alternative to single junction (SJ) solar cells trying to reduce the Staebler-Wronski Effect (SWE) and to increase the solar cell stability and efficiency. The dual-junction (DJ) solar cell is formed by a stack of two p-i-n a-Si:H solar cells (top and bottom solar cells) whose J-V characteristic curves are also studied. Important in this kind of device is an exact adjustment of the current generation in top and bottom cells since both cells are connected in series and therefore must generate the same short circuit current density (J <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">sc</inf> ). The J <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">sc</inf> could present a miss-matching due to the different absorption of light in deeper parts of the device if the thickness of top and bottom cell are not well adjusted. Changing the relation between the thickness of the active layers of the tandem solar cell, the miss-matching in the J <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">sc</inf> value between top and bottom solar cells can be minimized. The here developed computer simulations of the electrical and optical properties of the tandem device will help us to get a better understanding of tandem solar cells in order to design in a future work multi-junction solar cells made of different materials.