Interface properties and band alignment of Cu2S/CdS thin film solar cells

Development, fabrication and applications of CdS solar cells are reviewed in detail. The suitability of CdS cells for large solar panels and microcircuitry, and their low cost, are emphasized. Developments are reviewed by manufacturer-developer. Vapor phase deposition of thin-film solar cells, doping and co-evaporation, sputtering, chemical spray, and sintered layers are reviewed, in addition to spray deposition, monograin layer structures, and silk screening. Formation of junctions by electroplating, evaporation, brushing, CuCl dip, and chemiplating are discussed, along with counterelectrode fabrication, VPD film structures, the Cu2S barrier layer, and various photovoltaic effects (contact photovoltage, light intensity variation, optical enhancement), and various other CdS topics.

Cadmium sulfide solar cells

The optical and electronic properties of single crystal Cu2S-CdS photovoltaic cells were investigated. In these cells trapped charge near the interface which is manifested by a persistent increase in junction capacitance (the photocapacitance) plays a significant role in determining the carrier transport properties. It was found that the severe degradation in short-circuit current observed in heat-treated cells can be separated into two components: (1) a relatively small thermal component occurring on heat-treatment in the dark, and (2) a much larger degradation caused by exposure to light at room temperature. By a short additional heat-treatment above approximately 100 C the cell can be completely restored to its condition before the optically caused degradation with no effect on the depletion layer width.

/pdf/heat-treatment-effects-in-cu2s-cds-heterojunction-1rdbs0l2f3.pdf

Heat treatment effects in Cu2S-CdS heterojunction photovoltaic cells

The CdS/Cu2S solar cell: Basic operation and anomalous effects

The electronic structures and interface properties of the TiO₂/Cu₂S interface have been in situ studied after each growth step by x-ray and ultraviolet photoelectron spectroscopy The p-doped Cu₂S films (BEVBM=01 eV) were grown on the highly n-doped chemical vapor deposition prepared TiO₂ (BEVBM=34 eV) films by thermal evaporation in a multistep growth procedure The conduction band offset (07 eV), valence band offset (29 eV) and interface dipole (05 eV) were determined based on the quantitative examination of band bending occurring in the Cu2S films at higher coverage, leading to a staggered energy level configuration

In situ preparation and interface characterization of TiO2/Cu2S heterointerface

The influence of trapped charge on the photovoltaic properties of an efficient Cu2S-CdS single-crystal heterojunction has been studied by a photocapacitance technique. For the nonheat-treated cell, a persistent increment in capacitance as high as 70% of the dark capacitance remained after illumination of the junction by band-gap light at 100 K. The additional capacitance is due to holes trapped in deep levels in the CdS depletion region near the interface. The trapped holes enhanced the 100 K photocurrent spectrum uniformly by a factor of 3 before heat treatment. After a 200 C heat treatment in air, the maximum trapped charge at 100 K enhanced the photocurrent by two orders of magnitude. The results are interpreted in terms of the tunneling through a conduction band spike of electrons photoexcited in the Cu2S.

P. F. Lindquist

Papers

Photocapacitance Effects at a Cu2S–CdS Heterojunction