Abstract
The effect of Cu on highly efficient CdTe thin solid film cells with a glass/TCO/CdS/CdTe structure subjected to CdCl2 treatment was investigated by low-temperature photoluminescence (PL). The PL of the CdS/CdTe junction in samples without Cu deposition revealed a large shift in the bound exciton position due to the formation of CdSxTe1−x alloys with Eg (alloy) ≅ 1.557 eV at the interface region. After Cu deposition on the CdTe layer and subsequent heat treatment, a neutral acceptor-bound exciton (A0Cu,X) line at 1.59 eV and two additional band-edge peaks at 1.54 and 1.56 eV were observed, indicating an increase in the energy gap value in the vicinity of the CdTe/CdS interface to that characteristic of bulk CdTe. These results may suggest the disappearance of the intermixing phase at the CdTe/CdS interface due to the presence of Cu atoms in the junction area and the interaction of the Cu with sulfur atoms. Furthermore, an increase in the intensity of CdS-related peaks in Cu-doped samples was observed, implying that Cu atoms were incorporated into CdS after heat treatment.
Highlights
The low-temperature photoluminescence (PL) of CdTe single crystals has been intensively studied in the past [1,2]
It is very well known that the typical low-temperature spectrum of undoped single-crystal CdTe consists of bands assigned to the recombination of free excitons (FX), bound excitons (AX or DX), free-to-bound transitions (FB), and donor–acceptor pair (DAP) transitions
A typical CdTe solar cell consisting of a CdS/CdTe layer grown on a SnO2 /glass substrate is based on recombination within an n-CdS/p-CdTe heterojunction
Summary
The low-temperature photoluminescence (PL) of CdTe single crystals has been intensively studied in the past [1,2]. It is very well known that the typical low-temperature spectrum of undoped single-crystal CdTe consists of bands assigned to the recombination of free excitons (FX), bound excitons (AX or DX), free-to-bound transitions (FB), and donor–acceptor pair (DAP) transitions. Cu enters the CdTe interstitially forming a shallow donor, Cui centers and gives rise to deep doping [11,12,13,14,15,16]. Cu enters the CdTe interstitially forming a shallow donor, Cui centers and gives rise to acceptor CuCd centers via substitution [12,13,14,15]. Results of studies on the effect of Cu doping on the low-temperature front side PL of of CdS/CdTe solar cells will be presented.
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