Near surface defects: Cause of deficit between internal and external open‐circuit voltage in solar cells. (12th October 2021)

• Record Type: Journal Article
• Authors: Sood, Mohit; Urbaniak, Aleksander; Kameni Boumenou, Christian; Weiss, Thomas Paul; Elanzeery, Hossam; Babbe, Finn; Werner, Florian; Melchiorre, Michele; Siebentritt, Susanne
• Is Part Of: Progress in photovoltaics. Volume 30:Number 3(2022)
• Page Start: 263
• Page End: 275
• Publication Date: 2021-10-12
• Subjects: buffer layer -- deep acceptor -- defective layer -- quasi‐Fermi‐level splitting -- solar cell; Solar cells -- Periodicals; Photovoltaic cells -- Periodicals; Solar power plants -- Periodicals; 621.31245
• DOI: 10.1002/pip.3483
• Languages: English
• ISSNs: 1062-7995

Abstract

Abstract: Interface recombination in a complex multilayered thin‐film solar structure causes a disparity between the internal open‐circuit voltage ( V OC, in ), measured by photoluminescence, and the external open‐circuit voltage ( V OC, ex ), that is, a V OC deficit. Aspirations to reach higher V OC, ex values require a comprehensive knowledge of the connection between V OC deficit and interface recombination. Here, a near‐surface defect model is developed for copper indium di‐selenide solar cells grown under Cu‐excess conditions. These cell show the typical signatures of interface recombination: a strong disparity between V OC, in and V OC, ex, and extrapolation of the temperature dependent q · V OC, ex to a value below the bandgap energy. Yet, these cells do not suffer from reduced interface bandgap or from Fermi‐level pinning. The model presented is based on experimental analysis of admittance and deep‐level transient spectroscopy, which show the signature of an acceptor defect. Numerical simulations using the near‐surface defects model show the signatures of interface recombination without the need for a reduced interface bandgap or Fermi‐level pinning. These findings demonstrate that the V OC, in measurements alone can be inconclusive and might conceal the information on interface recombination pathways, establishing the need for complementary techniques like temperature dependent current–voltage measurements to identify the cause of interface recombination in the devices. Abstract : A numerical model based on experimental electrical characterisation results of CuInSe2 solar cell is introduced to comprehend the interface related loss in open‐circuit voltage in thin film solar cells. The model explains the source of difference between internal and external open‐circuit voltage and also reproduces activation energy less than the bandgap for the dominant recombination path, without having to make use of Fermi‐level pinning at the interface or of an unfavourable band alignment.