Even though absorber layers fabricated by different methods may yield comparable efficiencies and appear to be similar under conventional probes, such as low power Raman, PL, XRD, they could in fact be quite different in their microscopic structures. We have developed a novel nondestructive spectroscopy approach, high-power-high-temperature (HPHT) Raman spectroscopy, which is capable of revealing the microscopic structural variations of complex alloys like CZTSe over a large area. CZTSe films prepared by sputtering and co-evaporation methods were examined and compared in both lateral and depth directions. In general, high power (HP) illumination brought qualitatively different changes to the CZTSe samples, not only in the CZTSe Raman peaks but also in the secondary phases, which suggests that there is some subtle microscopic differences between the two types of samples. In addition, 2D Raman mapping revealed a larger spatial extension of the local heating effect caused by HP illumination in the sputtered film, which also indicates that two nominally similar films might have different thermal conductivities. High temperature (HT) measurement, which offers uniform heating as opposed to local heating with high power, further enhances the capability of the approach.

CdTe solar cells with a Te-buffer layer adjacent to the back contact were fabricated. The effects of the Te layer on cell performance were evaluated in detail. The carrier density of the Te layer (1018 cm-3) was measured. The valence band offset of the CdTe/Te interface (∼0.3-0.5 eV) was determined from current-voltage-temperature measurements and published reports. These values were incorporated into a simulation model and compared to the measured experimental performance with good agreement. Most notably, it was found that the Te layer allowed improved cell performance with less Cu required to form the back contact.

This work reports the fabrication and characterization of superstrate-type Zn1-xMgxO/CdTe heterojunction solar cells on both CdxSnyO and commercial SnO2:F transparent conducting oxides (TCOs) in which the ZMO and CTO layers are produced for the first time by hollow cathode sputtering. The sputtering is conducted in a reactive mode using metal or alloyed metal targets fitted to a custom-made linear cathode. It is notable that the CdS buffer layer conventionally employed in CdTe solar cells is entirely replaced by the ZMO window layer. The use of ZMO is found to eliminate the blue loss associated with CdS optical absorption and further results in a higher open-circuit voltage. Key parameters were found to be the conduction band offset at the ZMO/CdTe interface and the ZMO thickness. It was discovered that the ZMO exhibits intense photoluminescence even at room temperature. Most of the solar cells were fabricated in the FTO/ZMO/CdTe configuration although CTO/ZMO/CdTe solar cells were also demonstrated. The CTO was produced with an electron mobility of 46 cm2 V-1s-1 without any post-deposition annealing or treatment.

This study focuses on establishing a microstructural and morphological correlation between CIGS films and its precursor layer of Molybdenum (Mo) coated soda-lime glass (SLG). Therefore, variations in the morphology and microstructural properties of Mo thin films, using DC planar magnetron sputtering, were induced systematically by varying the sputtering pressure from 0.6 to 16 mT with a sputtering power density of 1.2 W/cm2. Subsequently, under fixed deposition conditions (deposition rate and substrate temperature), a growth of Cu(In,Ga)Se2 (CIGS) films was carried out on the Mo-coated SLG substrates, using the 3-stage growth process of the physical vapor deposition (PVD) technique.

High-Resolution Scanning Electron Microscopy (HRSEM) was used to examine the Mo and CIGS films morphology. X-Ray Diffraction (XRD) was applied to study in detail the microstructure of Mo and CIGS films. Where, the films’ crystal structure including the preferred orientation and the lattice parameters were determined by the θ/2θ XRD technique and by applying Cohen’s least-square method. Furthermore, Atomic Force Microscopy (AFM) was used to determine the root-mean-square (RMS) surface roughness of the CIGS films.

Molecular dynamics simulations of polycrystalline growth of CdTe/CdS heterostructures have been performed. First, CdS was deposited on an amorphous CdS substrate, forming a polycrystalline film. Subsequently, CdTe was deposited on top of the polycrystalline CdS film. Cross-sectional images show grain formation at early stages of the CdS growth. During CdTe deposition, the CdS structure remains almost unchanged. Concurrently, CdTe grain boundary motion was detected after the first 24.4 nanoseconds of CdTe deposition. With the elapse of time, this grain boundary pins along the CdS/CdTe interface, leaving only a small region of epitaxial growth. CdTe grains are larger than CdS grains in agreement with experimental observations in the literature. Crystal phase analysis shows that zinc blende structure dominates over the wurtzite structure inside both CdS and CdTe grains. Composition analysis shows Te and S diffusion to the CdS and CdTe films, respectively. These simulated results may stimulate new ideas for studying and improving CdTe solar cell efficiency.