Radio-frequency Plasma-enhanced Chemical Vapor Deposition Research Articles

Effects of fluorine incorporation on the structural and electrical properties of Diamond-like carbon

ABSTRACTDiamond-like carbon (DLC) has widespread attention as a new material for its application to thin film solar cells and other semiconducting devices. DLC can be produced at a lower cost than amorphous silicon, which is utilized for solar cells today. However, the electrical properties of DLC are insufficient for this purpose because of many dangling bonds in DLC. To solve this problem, we investigated the effects of the fluorine incorporation on the structural and electrical properties of DLC.We prepared five kinds of fluorinated DLC (F-DLC) thin film with different amounts of fluorine. Films were deposited by the radio-frequency plasma enhanced chemical vapor deposition (RF-PECVD) method. C6H6 and C6HF5 were used as source gases. The total gas flow rate was constant and the gas flow rate ratio R (=C6H6 / (C6H6 + C6HF5)) was changed from 0 to 1 in 0.25 ratio steps. We also prepared nitrogen doped DLC (F-DLC) on p-Si using N2 gas as a doping gas to form nitrogen doped DLC (F-DLC) / p-Si heterojunction diodes.X-ray photoelectron spectroscopy (XPS) showed that fluorine concentration in the DLC films was controlled. Moreover, the XPS analysis of the C1s spectrum at R=2/4 showed the presence of CF bonding. At R=1, CF2 bonding was observed in addition to CF bonding. The sheet resistivity of the films changed from 3.07×1012 to 4.86×109 Ω. The minimum value was obtained at R=2/4. The current-voltage characteristics indicated that nitrogen doped F-DLC of 2/4 and p-Si heterojunction diode exhibited the best rectification characteristics and its energy conversion efficiency had been maximized. This is because of a decrease of dangling bonds density by ESR analysis and an increase of sp2 structures by Raman analysis. When the fluorine is over certain content, the sheet resistivity increases because chain structures become larger, which is due to the CF2 bonding in F-DLC prevents ring structures. Many C2F4 species were observed and it may become precursors of the chain structure domains, such as (CF2)n.In this study, we revealed effects of fluorine incorporation on DLC and succeeded in increasing its conductivity and improving rectification characteristics of DLC/ p-Si hetero-junction diodes. Our results indicate that DLC fluorination is effective for the semiconducting material, such as solar cell applications.

Intermediate Layer Development for Laser-Crystallized Thin-Film Silicon Solar Cells on Glass

The intermediate layer (IL) between the glass and silicon plays an important role in laser-crystallized thin-film silicon solar cells. SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">X</sub> , SiN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">X</sub> , and SiC <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">X</sub> deposited by RF sputtering or plasma-enhanced chemical vapor deposition, either as single layers or in stacks, have been tested as ILs with regard to silicon wettability and silicon crystal quality and the effect of hydrogen passivation. SiC <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">X</sub> is the best wetting layer, allowing a larger laser crystallization process window than SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">X</sub> or SiN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">X</sub> . SiN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">X</sub> layers are limited by pinholing, which increases in severity with laser fluence. SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">X</sub> ILs result in lower silicon grain-boundary density compared with SiC <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> -based layers and to SiN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">X</sub> -based layers. Hydrogen passivation of laser-crystallized silicon on single layer SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">X</sub> has no impact on V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">OC</sub> , while an improvement of around 60 mV is found for samples on SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> /SiN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> /SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> stacks. Diffusion of dopants from the IL are found to create a uniformly doped absorber with no evidence of a front-surface field.

Synthesis of Carbon Nanowalls and Few-Layer Graphene Sheets on Transparent Conductive Substrates

Abstract We report on the growth of carbon nanowalls and few-layer graphene sheets on glass substrates coated with different transparent conductive oxides or gold. The growth is accomplished by a capacitively-coupled radio-frequency plasma-enhanced chemical vapor deposition setup with a gas mixture of C2H2, H2, and Ar or He. This system allows the synthesis of thin vertical carbon nanosheets without catalyst at mild reaction conditions due to the low plasma density, which is preferable for sensitive substrate materials. In fact, the electrical properties of the transparent conductive indium tin oxide and fluorine-doped tin oxide stay intact upon carbon growth. Carbon nanowalls and few-layer graphene sheets on transparent conductive oxides are promising candidates for solar-cell applications while these nanostructures on gold coated glass can act as catalyst support material.

Effects of frequency of pulsed substrate bias on structure and properties of silicon-doped diamond-like carbon films by plasma deposition

We have investigated the effects of the frequency of pulsed substrate bias on the structure and properties of Si-doped diamond-like carbon (Si-DLC) films deposited by radio-frequency plasma-enhanced chemical vapor deposition using CH4, Ar, and monomethylsilane (CH3SiH3) as the Si source. The Si/(Si+C) ratios in the Si-DLC films deposited using pulsed bias were higher than that of the dc-biased Si-DLC film, and the Si fraction increased with decreasing frequency. Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy analyses revealed that Si–C, Si–Hn, and C–Hn bonds in the Si-DLC films increased with decreasing frequency. The internal stress decreased as the frequency decreased, which is probably due to the increase in Si–C, Si–Hn, and C–Hn bonds in the films. It was found that the wear rate of the pulse-biased Si-DLC film deposited at the highest frequency in this study is comparable to that of the dc-biased, undoped DLC film. Furthermore, the friction coefficient of the former is about one third of that of the latter.

Microstructure and properties of silicon-incorporated DLC film fabricated using HMDS gas and RF-PECVD process.

The microstructure and characteristics of silicon-incorporated diamond-like carbon film, fabricated using a radio-frequency plasma-enhanced chemical vapor deposition process with hexamethyldisilane [(CH3)3,Si x Si(CH3)3:HMDS] gas as a silicon source, were investigated. Diamond-like carbon films with silicon compositions from 0 to 5 atomic percent were deposited onto ultra-fine grained AZ31 magnesium alloy substrate as buffer layers or multilayers. Si doping led not only to an increase in the bonding ratio (sp3/sp2), but improvements in hardness, critical adhesion, and corrosion resistance. Out of the investigated samples, the multi-deposited silicon diamond-like carbon thin film on magnesium substrate showed the best combination of adhesive, wear resistance, and corrosion resistance properties.

A novel method to make boron-doped microcrystalline silicon thin films with optimal crystalline volume fraction for thin films solar cell applications.

Highly conducting boron-doped microcrystalline silicon (p-type μc-Si:H) thin films have been prepared by radio frequency plasma-enhanced chemical-vapor deposition (RF-PECVD). In this work, the effects of hydrogen dilution, doping ratio, plasma power, deposition pressure and substrate temperature on the growth and the properties of boron-doped microcrystalline silicon (p-type μc-Si:H) thin films are investigated. The electrical, chemical and structural properties are improved with increasing crystallite, which depends on the plasma conditions. For various plasma parameters, the crystalline volume fraction (X(c)), dark conductivity (σ(d)), activation energy (E(a)), hydrogen content (C(H)), surface roughness (S(r)), and micro void fraction (R*) were measured, and they were 0-72%, 4.17-10(-4) S/cm-1.1 S/cm, 0.041-0.113 eV, 3.8-11.5 at.%, 3.2 nm-12.2 nm, and 0.47-0.80, respectively. The film with R* of 0.47 and C(H) of about 5 at.% belonged to a region of low disorder, and acted as a good passivation layer.

Investigation on Microstructure and Optical Property of Nanocrystalline Silicon Thin Film

Nanocrystalline silicon (nc-Si:H) thin films were deposited by capacitive coupled radio-frequency plasma enhanced chemical vapor deposition (RF-PECVD) system with direct current (DC) bias applied. Raman, XRD and ultraviolet-visible transmission spectra were employed to investigate their microstructure and optical properties, respectively. Both the crystalline volume fraction and the average crystalline size increase with the substrate temperature. With the increase of silane concentration, the crystalline volume fraction increases, while the average crystalline size decreases. With the increase of the radio frequency (RF) power or the DC negative bias voltage, the crystalline volume fraction and the average crystalline size increase firstly, then decreases. Finally, the optical band gaps were discussed in detail.

Control of crystalline volume and nano crystal grain size in nanocrystalline silicon thin film deposited by PECVD

Application of the radio frequency plasma enhanced chemical vapor deposition (RF-PECVD) technique was studied to fabricate amorphous and nanocrystalline silicon (a-Si and nc-Si) thin films for photovoltaic devices at substrate temperature of 200 °C. Amorphous-crystalline transition of silicon thin films in working conditions of PECVD system was shown as a function of deposition parameters, i.e., dilution ratio of silane (SiH 4 ) in hydrogen, total gas pressure during deposition and RF excitation power density. The crystalline volume as well as grain size of nanocrystalline silicon films could be successfully controlled by tuning those deposition parameters. Micro Raman scattering spectroscopy and spectroscopic ellipsometry (SE) methods were used to characterize the structure and crystallization of the deposited silicon thin films. We could make nc-Si thin films with various crystalline volumes. Nc-Si grain size was also controlled and was in the range of 3–5 nm.

Fabrication of single junction amorphous silicon solar cell/mini module using novel n-type nanocrystalline SiOx:F:H back reflector

A novel n-type nanocrystalline hydrogenated and fluorinated silicon oxide (nc-SiOx:F:H) based back reflector layer (BRL) has been successfully developed for the fabrication of amorphous silicon based single junction solar cells by radio frequency plasma enhanced chemical vapor deposition (RF-PECVD) technique. Optoelectronic properties, particularly the refractive index (n) suitable for BRL were controlled by varying the oxygen content within the film without compromising the essential nanocrystalline growth. Surface morphology, structural and optical analysis of nc-SiOx:F:H were investigated by using AFM, HRTEM, Raman, FTIR and Ellipsometer. Advantage of this nanocrystalline material as BRL has been demonstrated by incorporating it into a single junction amorphous silicon solar cell and compared its performance with conventional aluminium doped zinc oxide (ZnO:Al) and n doped hydrogenated microcrystalline silicon oxide (n-µc-SiOx:H) based BRL. Single junction thin film a-Si solar cells with initial efficiency ~9.66 % have been successfully fabricated. It is found that the solar cell fabricated using newly developed BRL shows ~6 % more efficiency compared to n-µc-SiOx:H based BRL. Spectral response studies revealed that the improvement was mainly due to enhanced response at visible as well as higher wavelength region.

Direct versatile PECVD growth of graphene nanowalls on multiple substrates

In this paper, we demonstrated a simple and versatile technique to directly produce high-quality graphene nanowalls (GNWs) on multiple substrates by radio frequency plasma enhanced chemical vapor deposition (RF-PECVD) at 750°C without any catalyst and post-transfer. Similar morphologies and structures obtained under the same preparation process on different substrates revealed that the growth of GNWs was not sensitive to substrate. It was proposed that the GNWs grew via Volmer-Weber mechanism. The stresses from colliding islands would change the growth direction vertically upward. Then the erect growth along the edges would rely less on substrates. Owing to super-large surfaces and outstanding photoelectric properties, GNWs could bring broad applications of nanodevices.

Experimental investigations into the formation of nanocrystal silicon thin film synthesized at low substrate temperature

In this study, nanocrystal silicon (nc-Si) films were synthesized via radio-frequency plasma-enhanced chemical-vapor deposition with argon and hydrogen diluted silane. In such a high-density reactive plasma medium, nc-Sis are formed in the plasma first and are then deposited into the film by the fast gas flow. The plasma electronic diagnostics indicate nanoparticle formation in the plasma, as opposed to solid-state nucleation of the nanoparticles in the film. The construction and photoluminescence (PL) were investigated. As power provided to the plasma source increases, the particles transition from amorphous to crystalline, and a corresponding increase in the fraction of hydrogen bonded on a crystalline silicon surface is observed. The oxidized nc-Si films show obvious phase separation without high-temperature annealing. Further, PL measurements show that the increase in photoluminescence intensity of nc-Si films after oxidation is due to an efficient surface passivation with oxygen.

High open-circuit voltage (1.04 V) n–i–p type thin film silicon solar cell by two-phase silicon carbide intrinsic material

We prepared two-phase hydrogenated silicon carbide (SiC:H) intrinsic materials from silane–methane gas mixtures at a low temperature of 150°C using radio-frequency plasma enhanced chemical vapor deposition (RF-PECVD). We then employed Raman, HRTEM and FT-IR measurements to investigate the structural evolution of the resulting two-phase heterostructure films, and confirmed the medium range order of SiC:H materials based on the intensity of the transverse acoustic mode and microstructure factor. High concentration of medium order materials associated with nanocrystalline Si was obtained in the amorphous silicon carbide/nanocrystalline silicon hybrid layers. Under optimized deposition conditions, the intrinsic film has an optical band gap of up to ~2.0eV and photosensitivity of up to ~4×106; these qualities make it an excellent intrinsic material to use when fabricating wide band gap top cells for multi-junction thin film silicon solar cells. Using both wide band gap window layers and intrinsic layers, a high open-circuit voltage of 1.04V and short-circuit current density of 9.66mA/cm2 were achieved for a single junction n–i–p solar cell on stainless steel.

RF-PECVD growth and nitrogen plasma functionalization of CNTs on copper foil for electrochemical applications

This work describes an efficient way to improve the adhesion, growth rate and density of CNTs on copper substrate using radio-frequency plasma enhanced chemical vapor deposition (RF-PECVD). The adhesion of an alumina buffer layer to the copper substrate is critical for the successful growth of CNTs. Hydrogen plasma was performed on the copper substrate to reduce copper oxide from the surface. The effect of two intermediate layers (Ti, Ni), as individual or in combination, between alumina and copper substrate on the CNT growth has been investigated. Furthermore, a nitrogen plasma treatment was carried out to functionalize the obtained CNTs. Electrochemical measurements were performed using CNTs grown on a copper substrate as electrodes and LiClO4 as electrolyte. The specific capacitance of the obtained electrodes increases from 49 up to 227Fg−1 for untreated and nitrogen-plasma treated CNTs at a scan rate of 10mVs−1, respectively.

Improved amorphous/crystalline silicon interface passivation for heterojunction solar cells by low-temperature chemical vapor deposition and post-annealing treatment

In this study, hydrogenated amorphous silicon (a-Si:H) thin films are deposited using a radio-frequency plasma-enhanced chemical vapor deposition (RF-PECVD) system. The Si-H configuration of the a-Si:H/c-Si interface is regulated by optimizing the deposition temperature and post-annealing duration to improve the minority carrier lifetime (τeff) of a commercial Czochralski (Cz) silicon wafer. The mechanism of this improvement involves saturation of the microstructural defects with hydrogen evolved within the a-Si:H films due to the transformation from SiH2 into SiH during the annealing process. The post-annealing temperature is controlled to ∼180 °C so that silicon heterojunction solar cells (SHJ) could be prepared without an additional annealing step. To achieve better performance of the SHJ solar cells, we also optimize the thickness of the a-Si:H passivation layer. Finally, complete SHJ solar cells are fabricated using different temperatures for the a-Si:H film deposition to study the influence of the deposition temperature on the solar cell parameters. For the optimized a-Si:H deposition conditions, an efficiency of 18.41% is achieved on a textured Cz silicon wafer.

Boron doped nanocrystalline silicon/amorphous silicon hybrid emitter layers used to improve the performance of silicon heterojunction solar cells

Boron doped nanocrystalline silicon/amorphous silicon hybrid thin films were deposited by radio frequency plasma enhanced chemical vapor deposition (RF-PECVD) to improve the performance of silicon heterojunction (SHJ) solar cells. Electrical and optical properties as well as structural and passivation characteristics of these thin films were systematically researched as a function of TMB gas mixture ratio. A high dark conductivity of 6.5×10−4S/cm and minority carrier lifetime (τs) of 1740μs on Czochralski (Cz) Si wafers were obtained with the hybrid p-type Si films. We applied this optimized film as an emitter layer on SHJ solar cells based on Cz silicon wafers; a significant improvement in the solar cell wavelength response at 400nm and output performance have been achieved.

High temperature nano-coated electric-arc-induced long-period gratings working at the dispersion turning point for refractive index sensing

In this paper we present for the first time electric-arc-induced long-period gratings (LPGs) working at the dispersion turning point (DTP) in the wavelength range of about 1550 nm. The DTP is achieved by reducing the grating period down to about 190 µm. In contrast to LPGs fabricated with the typical UV laser-based method, arc-induced gratings show high thermal stability and excellent long-term performance. These advantages make it possible to coat the LPGs using thin-film deposition methods, which require high temperatures. We present the effect of thin silicon nitride (SiNx) overlay deposited by the radio-frequency plasma-enhanced chemical vapor deposition (RF PECVD) method. This technique increased the refractive index sensitivity of the LPGs from 400–700 nm/refractive index unit (RIU) to 887–2146 nm/RIU.

Optical absorption enhancement of μc-SiGe:H films deposited via high pressure and high power

Hydrogenated microcrystalline silicon-germanium (μc-SiGe:H) films are fabricated by radio-frequency plasma-enhanced chemical vapor deposition (RF-PECVD). The optical absorption coefficient and the photosensitivity of the μc-SiGe:H films increase dramatically by increasing the plasma power and deposition pressure simultaneously. Additionally, the microstructural properties of the μc-SiGe:H films are also studied. By combining Raman, Fourier transform infrared (FTIR) and X-ray fluoroscopy (XRF) measurements, it is shown that the Ge-bonding configuration and compactability of the μc-SiGe:H thin films play a crucial role in enhancing the optical absorption and optimizing the quality of the films via a significant reduction in the defect density.

Design and Deposition of Infrared Antireflection Protection Film on Magnesium Fluoride Substrate for 3~5 μm

The infrared antireflection protection film is designed and deposited on magnesium fluoride substrate for 3~5 μm. The multilayer antireflection film is designed and prepared by ion beam assisted electron-beam deposition. After repeated experiments, the absorption peak of SiO2 is found at 3000nm,using MgF2 and SiO2 as the low-index materials to reduce the absorption. The coating structure is Sub|1.46H1.37L2.19H1.45L2.49M|Air. DLC (diamond-like carbon) protection coating is deposited by radio frequency plasma enhanced chemical vapor deposition (RF-PECVD). Through contrast tests, the best deposition process is obtained (the butane flow rate is 5sccm/s, deposition temperature is 80°C) by setting deposition time as invariant, the reaction gas flow rate and deposition temperature as variables. Meanwhile the problem of associativity between antireflection film and DLC protection coating is solved by adding a Si transition layer. The result shows that the average transmittance of this film in 3~5μm is 95.5%, and this film can withstands harsh environment tests. Key words: Magnesium fluoride substrate; Antireflection protection film; 3~5 μm infrared band Document Code: A Article ID: DIO

RF-PECVD deposition and optical properties of hydrogenated amorphous silicon carbide thin films

Hydrogenated amorphous silicon carbide (a-SiCx:H) thin films were deposited using a radio frequency plasma enhanced chemical vapor deposition (RF-PECVD) system with methane (CH4) and silane (SiH4) as reactive precursor gases and H2 as a carrier and dilution gas. The effects of RF-PECVD deposition conditions on the optical properties and microstructural characteristics of a-SiCx:H thin films were systematically investigated. When the RF power density, deposition pressure (P) and temperature (Ts) were fixed, the refractive index (n) and the growth rate of a-SiCx:H thin films decreased with the CH4/SiH4 flow rate ratio (R), while their optical band gap (Eg) increased with R. The a-SiCx:H thin film grown at higher R was found to be smoother than that grown at lower R. When the RF power density, P and R were fixed, the growth rate of a-SiCx:H thin films decreased with Ts, while their n increased with Ts. It was found that Eg slightly increased with Ts, and the film became rough at higher Ts. When Ts, P and R were fixed, the growth rate of a-SiCx:H thin films increased with the RF power density, while their n only slightly increased and Eg slightly decreased with the RF power density. It was found that the RF power density had a large impact on the roughness of a-SiCx:H thin films.

Applications of real-time and mapping spectroscopic ellipsometry for process development and optimization in hydrogenated silicon thin-film photovoltaics technology

Four applications of real-time spectroscopic ellipsometry (RTSE) and ex-situ mapping spectroscopic ellipsometry (SE) in thin-film hydrogenated silicon (Si:H) photovoltaics (PV) technology are reviewed with the common theme being the development and application of SE-derived growth evolution diagrams. The goals of these applications are to understand and consequently further advance this technology. In the first application, fabrication of engineered thin films consisting of periodic arrays of silicon (Si) nanocrystallites in an amorphous Si:H (a-Si:H) host matrix has been guided by a growth evolution diagram developed by RTSE for radio-frequency plasma-enhanced chemical vapor deposition (PECVD) using SiH4+H2 mixtures. Such precisely controlled microstructures are of interest as possible intrinsic-layer components of p–i–n and n–i–p thin-film PV devices, and RTSE is shown to be a key technique for guidance in fabrication and for structure verification. In the second application of growth evolution diagrams, very-high-frequency PECVD intrinsic a-Si:H, hydrogenated amorphous silicon–germanium alloys (a-Si1−xGex:H), and hydrogenated nanocrystalline silicon (nc-Si:H) have been investigated for use as the top, middle, and bottom-cell i-layer components, respectively, of triple-junction n–i–p solar cells. The growth evolution diagram for the bottom-cell i-layer, starting from an underlying mixed-phase amorphous+nanocrystalline silicon [(a+nc)-Si:H] n-layer, reveals a bifurcation at a critical H2-dilution flow ratio R (R=[H2]/[Si2H6], in this application) between mixed-to-amorphous phase evolution [(a+nc)→a] at low R and mixed-to-nanocrystalline phase evolution [(a+nc)→nc] at high R. The highest performance single-step nc-Si:H solar cell is found at minimal R while remaining on the nanocrystalline side of the identified bifurcation where suitable grain boundary passivation can be assured. Because of the importance of the roll-to-roll flexible substrate configuration in such multijunction Si:H-based PV technology, RTSE has been demonstrated in a third application for monitoring PECVD of a-Si:H n–i–p solar cell structures on back-reflector-coated flexible roll-to-roll polymer substrates. RTSE has been used for probing along the center line of the moving substrate during deposition, and ex-situ mapping SE has been used over the full substrate area after deposition. Detailed studies of the top-most p-layer of the n–i–p solar cell have been performed, with the goal being to develop spatially-dependent (in contrast to R-dependent) growth evolution diagrams in order to evaluate uniformity across the width of the substrate and thus to enable optimization of the resulting a-Si:H PV modules. In this study, efficiency optimization occurs at the p-layer transition region in which a-Si:H nucleates from the i-layer surface, but evolves to predominantly nc-Si:H for improved contact to the top-most In2O3:Sn layer. In the fourth and final application reviewed here, the mapping-SE-deduced properties of the Si:H i and p-layers have been spatially correlated with device performance parameters from an array of n–i–p a-Si:H-based dot cells over a 13×13cm2 substrate area. Analysis of the SE data acquired over the full area provides property maps of i-layer thickness and band gap, p-layer thickness and band gap, and p-layer surface roughness thickness for the n–i–p structure. The mapped values adjacent to the PV devices have been correlated with the device performance parameters. When sufficient non-uniformity exists, these correlations enable optimization based on specific ranges of values that characterize the fundamental properties of the material and the film structure.