Current transport studies of amorphous n/p junctions and its application in a‐Si:H/HIT‐type tandem cells. (4th July 2015)

• Record Type: Journal Article
• Authors: Lee, Youngseok; Dao, Vinh Ai; Iftiquar, S. M.; Kim, Sangho; Yi, Junsin
• Is Part Of: Progress in photovoltaics. Volume 24:Number 1(2016)
• Page Start: 52
• Page End: 58
• Publication Date: 2015-07-04
• Subjects: recombination tunneling junction -- current transport -- a‐Si:H/HIT‐type tandem solar cell; Solar cells -- Periodicals; Photovoltaic cells -- Periodicals; Solar power plants -- Periodicals; 621.31245
• DOI: 10.1002/pip.2644
• Languages: English
• ISSNs: 1062-7995

Abstract

Abstract: This paper presents an understanding of the fundamental carrier transport mechanism in hydrogenated amorphous silicon (a‐Si:H)‐based n/p junctions. These n/p junctions are, then, used as tunneling and recombination junctions (TRJ) in tandem solar cells, which were constructed by stacking the a‐Si:H‐based solar cell on the heterojunction with intrinsic thin layer (HIT) cell. First, the effect of activation energy ( E a ) and Urbach parameter ( E u ) of n‐type hydrogenated amorphous silicon (a‐Si:H(n)) on current transport in an a‐Si:H‐based n/p TRJ has been investigated. The photoluminescence spectra and temperature‐dependent current–voltage characteristics in dark condition indicates that the tunneling is the dominant carrier transport mechanism in our a‐Si:H‐based n/p‐type TRJ. The fabrication of a tandem cell structure consists of an a‐Si:H‐based top cell and an HIT‐type bottom cell with the a‐Si:H‐based n/p junction developed as a TRJ in between. The development of a‐Si:H‐based n/p junction as a TRJ leads to an improved a‐Si:H/HIT‐type tandem cell with a better open circuit voltage ( V oc ), fill factor ( FF ), and efficiency. The improvements in the cell performance was attributed to the wider band‐tail states in the a‐Si:H(n) layer that helps to an enhanced tunneling and recombination process in the TRJ. The best photovoltage parameters of the tandem cell were found to be V oc = 1430 mV, short circuit current density = 10.51 mA/cm 2, FF = 0.65, and efficiency = 9.75%. Copyright © 2015 John Wiley & Sons, Ltd. Abstract : Enhanced tunneling of charge carriers across a‐Si:H(n)/a‐Si:H(p) junction was observed when phosphorus doping of the n‐type layer was increased. Such a tunneling and recombination junction was used in a tandem cell, consisting on p‐i‐n type amorphous silicon top cell and a heterojunction with intrinsic thin layer‐type bottom cell. In the tandem cell, the tunnel junction helped in improving cell efficiency.