Multiple polycrystalline CdS/CdTe solar cells with efficiencies greater than 15% were produced on buffered, commercially-available Pilkington TEC Glass TM at EPIR Technologies, Inc. (EPIR) and verified by the National Renewable Energy Laboratory (NREL). n-CdS and p-CdTe were grown by chemical bath deposition (CBD) and close space sublimation, respectively. Samples with sputter-deposited CdS were also investigated. Initial results indicate that this is a viable dry-process alternative to CBD for production-scale processing. Published results for polycrystalline CdS/CdTe solar cells with high efficiencies are typically based upon cells utilizing research-grade transparent conducting oxides (TCOs) requiring high-temperature processing inconducive to low-cost manufacturing. EPIR's results for cells on commercial glass were obtained by implementing a high resistivity SnO 2 buffer layer and optimizing the CdS window layer thickness. The high resistivity buffer layer prevents the formation of CdTe-TCO junctions, thereby maintaining a high open circuit voltage and fill factor; while using a thin CdS layer reduces absorption losses and improves the short circuit current density. EPIR's best device demonstrated an NREL-verified efficiency of 15.3%. The mean efficiency of hundreds of cells produced with a buffer layer between December 2010 and June 2011 is 14.4%. Quantum efficiency results are presented to demonstrate EPIR's progress toward NREL's best-published results.
A new photoconductor device structure is described utilizing a heterojunction contact which incorporates a higher band-gap HgCdTe alloy between the metal contact and the normal band-gap photoconductor. A theoretical treatment of the heterojunction contact photoconductor (HCP) device shows that carrier sweepout can be virtually eliminated; the calculations predict elimination of ‘‘saturation’’ of responsivity and a very large increase in responsivity. HCP devices were fabricated; experimental results verified the theory in several ways. A responsivity was measured at 80 K of about 450 000 V/W at 30 V/cm and over 1 500 000 V/W at 125 V/cm.
To reduce the manufacturing cost, soda-lime glass (SLG) is often used as the substrate for thin-film solar cells. It is known that SLG contains about 16 wt% Na in the form of Na2O. During the growth of thin films, Na ions may diffuse out from SLG and diffuse into the grown thin films and affect the optoelectronic properties of the thin films. The widely used commercial F-doped Sn2O (FTO) glass (Teck 15) has the structure SLG/FTO/SiO2/FTO. The first FTO layer and the SiO2 layer are very thin. The SiO2 layer is often expected to be a barrier layer for Na out-diffusion from SLG. However, our transmission electron microscopy (TEM) study indicates that there is a significant amount of Na existing in the second FTO layer, further indicating that SiO2 may not be a good barrier layer for Na out-diffusion. Therefore, we have investigated the possibility of a SiO2 layer as a barrier layer for Na out-diffusion from SLG. We have deposited two types of samples, SLG/SiO2/FTO and SLG/FTO, at 550°C. For comparison, these samples were also annealed at temperatures between 550° and 650°C. The as-deposited and annealed samples were examined by TEM, X-ray energy dispersive spectroscopy (EDS) and secondary-ion mass spectrometry (SIMS). We found that SiO2 is indeed an effective barrier layer for Na outdiffusion. Thermal annealing can enhance Na diffusion. It should be pointed out that our deposited SiO2 layer may behave differently from the SiO2 layer seen in the commercial FTO-coated glass.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.