The effects of pressure on the fabrication of CdS/CdTe thin film solar cells made via pulsed laser deposition

Abstract

CdS/CdTe thin film solar cells with 100 nm CdS and 1.0-1.5 µm CdTe have been made in situ using pulsed laser deposition (PLD). This work intends to investigate the effect of PLD chamber pressure on the CdTe absorber layer. In particular, a comparison between two specific cases of Ar at 8% of O 2 and pure O 2 was made to elucidate the role of O 2 and Ar in formation and physical properties of the CdTe absorber. At the same O 2 partial pressure of 1.2 torr, an efficiency of 6.4% was obtained in the latter case, which represents a considerable improvement over the former case with the best efficiency of 6.7% previously reported which utilized a 1.5 µm CdTe layer. This result suggests that the availability of oxygen near the growing CdTe film is important during PLD of CdTe layers and the better performance in PLD of CdTe in pure O 2 may be attributed to the more preserved kinetic energy of the reaction species due to the reduced total gas pressure.

Development of Combinatorial Pulsed Laser Deposition for Expedited Device Optimization in CdTe/CdS Thin-Film Solar Cells

“…The PLD system consists of a 248 nm KrF excimer laser from Lambda Physik with a 20 ns laser pulse duration. The absorber and window layer targets are mounted inside a vacuum chamber on rotating stands that allow for both targets to be moved into the path of the laser and rotation about the axis of the targets facilitates uniform ablation of the target surface [7,8,[10][11][12]. The CdS and CdTe targets were obtained from ACI Alloys and had a 99.99% purity.…”

“…PLD is a relatively new fabrication technique applied for CdTe solar cells. While its application to solar cells has proven effective in past research, a systematic study of the effect of the PLD processing conditions is lacking [7,8]. PLD is advantageous for thin-film depositions due to its highly controllable deposition rate and also its many easily adjustable ablation parameters including laser repetition rate, pulse length, energy density, target-substrate distance, and chamber atmosphere and temperature [9].…”

Microstructure Analysis of Cdte/CDS Thin-Film Solar Cells for Optimization of Devices Fabricated at Low Temperature With Pulsed Laser Deposition

“…The energy densities of roughly 0.7 J/cm 2 and 0.6 J/cm 2 at the target surface were used for depositing CdTe and CdS, respectively. [13,20,21] A scanning stage controlled by computer was used to move the substrate in the plane perpendicular to the plume direction for large area uniformity. The sample to target distance was 5.5 cm.The base pressure was 5.0x10 -6 Torr.…”

“…In particular, it is compatible to the CdCl 2 annealing (360ºC for 15 minutes in mixed (4:1) Ar/O 2 gases of atmospheric pressure) applied after the PLD fabrication for improvement of the CdTe grain connectivity and charge carrier doping. [10,13,14,[20][21][22] Br:CH 4 O etching (0.2mL:40mL) for four seconds was employed to create a Te rich surface for better Ohmic back contact of(HgTe:Cu):graphite paste (253:1):2.5. To further reduce the contact resistance, the cells were annealed in a furnace at280ºC for 30 minutes in Ar gas.…”

“…In a recent work, we have demonstrated the feasibility ofPLD deposition of CdS/CdTe thin films solar cells ata temperature of 500ºC for CdTe PLD fabrication. [13,14]Power conversion efficiency up to 5% has been demonstrated. However, the uniformity of such devices was poor, most probably due to the high substrate temperature (T s ),exceeding500 C, compared to other typical methods for depositing CdTe, such as close-space sublimation.…”