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ABSTRACT Thin CdTe photovoltaic device efficiencies show significant improvement with the incorporation of a CdSeTe alloy layer deposited between a MgZnO emitter and CdTe absorber. CdTe and CdSeTe/CdTe devices fabricated by close-space sublimation with a total absorber thickness of 1.5 µm are studied using microscopy measurements and show minimal diffusion of Se into the CdTe. Current loss analysis shows that the CdSeTe layer is the primary absorber in the CdSeTe/CdTe structure, and fill factor loss analysis shows that ideality-factor reduction is the dominant mechanism of fill factor loss. Improvement in the CdSeTe/CdTe absorber quality compared to CdTe is also reflected in spectral and time-resolved photoluminescence measurements. Current density vs. voltage measurements show an increase in current density of up to 2 mA/cm 2 with the addition of CdSeTe due to a band gap shift from 1.5 to 1.42 eV for CdTe and CdSeTe/CdTe absorbers respectively. Voltage deficit is lower with the incorporation of the CdSeTe layer, corroborated by improved electroluminescence intensity. The addition of CdSeTe into CdTe device structures has increased device efficiencies from 14.7% to 15.6% for absorbers with a total thickness less than two microns.
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Understanding the Role of CdTe in Polycrystalline CdSe x Te 1–x /CdTe‐Graded Bilayer Photovoltaic Devices
Grading of bandgap by alloying CdTe with selenium to form a CdSexTe1–x/CdTe‐graded bilayer device has led to a device efficiency over 19%. A CdSexTe1–xabsorber would increase the short‐circuit current due to its lower bandgap but at the expense of open‐circuit voltage. It has been demonstrated that adding a CdTe layer at the back of such a CdSexTe1–xfilm reduces the voltage deficit caused by the lower bandgap of absorber from selenium alloying while maintaining the higher short‐circuit current. This leads to a photovoltaic device that draws advantage from both materials with an efficiency greater than either of them. Herein, a detailed account using device data, ultraviolet photoelectron spectroscopy, electron microscopy, and first‐principles density functional theory modeling is provided, which shows that CdTe acts as an electron reflector for CdSexTe1–x.
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- Award ID(s):
- 1821526
- PAR ID:
- 10302573
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Solar RRL
- Volume:
- 5
- Issue:
- 11
- ISSN:
- 2367-198X
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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