This PDF file contains the front matter associated with SPIE Proceedings Volume 8110, including the Title Page, Copyright information, Table of Contents, Introduction, and the Conference Committee listing.

HelioVolt Corporation is currently developing Copper Indium Gallium Selenide (CIGS) products using a solution-based deposition of precursor films followed by rapid optical processing (ROP) to make CIGS. The ROP process takes less than 1 minute of heating to convert the precursor stack to CIGS. Device made with ROP rival performance of device processed using field assisted simultaneous synthesis and transfer (FASST®) processing.

CuIn_1-xGa_xSe₂ (CIGS) films were prepared by a RF sputtering system using a CIGS single target having a composition of CuIn_0.75Ga_0.25Se₂. X-ray diffraction measurements confirmed that CIGS films grown on Mo-coated soda-lime glass at 350 °C exhibited only (112) diffraction, while CIGS films annealed at 550 °C and for 30 min in rapid thermal annealing (RTA) chamber showed (112), (220), (312), and other diffraction peaks of the chalcopyrite structure. The CIGS films annealed showed much higher intensity of (112) diffraction than that of the films grown at 350 °C, demonstrating improvement of crystal-quality of the films. However, no peaks originated from other phase were observed. The average composition of the CIGS films determined by energy dispersive x-ray spectrometer (EDX) was in good agreement with that of the target. Furthermore, secondary ion mass spectrometry (SIMS) analysis revealed that RTA treatment for Mo layer prior to CIGS film deposition suppresses the inter-diffusion of In, Ga, and Mo at the interface. These results demonstrate that RF sputtering of CIGS single target can be a promising method to fabricate high-quality CIGS films and heat treatment of Mo layer is indispensible to control the interface of CIGS/Mo.

A method of non-vacuum synthesis of CuInSe₂ (CIS) thin films is presented. The method is based on electrophoretic deposition (EPD) of Cu-In composite nanoparticles in liquid solvents. Colloidal suspensions of Cu-In composite nanoparticles are prepared with pulsed laser ablation without additional stabilizing agents. The charge acquisition of the nanoparticles in solvents, deposition of particles on electrode surfaces will be explained. After selenization in selenium vapor in atmospheric pressure, polycrystalline CIS films and solar cell devices are produced. We will demonstrate EPD as a new choice of low-cost synthesis of thin film solar absorbers.

Metallic inclusions in layered structures can have noticeable effects onto scattering and absorption due to the coupling of the external electromagnetic field and local charge oscillations. These effects are strongly related to both the geometry of the individual particle as well as to the array structure. Having in mind the efficiency improvement of silicon solar cells due to plasmonic effects, we report on the modeling and the fabrication of periodic arrays of metallic nanoparticles on planar substrates. Different characterization techniques as atomic force microscopy (AFM), scanning electron microscope (SEM) and optical measurements are applied which provide particular information with respect to the fabricated structures, each. Special emphasis is placed on the clarification of the dominant features of the optical characterization by detailed numerical analysis. This allows identifying significant modes of the planar geometry which is complemented by the nanostructures, whose interplay with the radiation field does establish changes of the absorption in the silicon layer, finally. These findings may be helpful for optimization and clarification of specific details of technology, later on.

We present an approach to estimating the light-trapping of thin film silicon solar cells by comparing the measured quantum efficiency spectrum and the theoretical absorptance spectrum based on ideal diffractive light scattering. The ideal diffractive absorptance enhancement is about 50 in silicon-based cells. We have surveyed published results for many nanocrystalline silicon cells; the largest empirical enhancement is about 25. We discuss the physical mechanisms leading to the reduced quantum efficiencies.

Rigorous coupled-wave analysis was used to compute the absorptance of a metallic surface-relief grating coated with a semiconductor layer. The grating is formed by periodic bumps on an otherwise planar layer of a suitable metal. When the period of the surface-relief grating is appropriate, at a certain incidence angle the incident light excites a p-polarized surface-plasmon-polariton (SPP) wave if the semiconductor layer is homogeneous. However, if the semiconductor layer is periodically non-homogeneous normal to the mean metal/semiconductor interface, more than one SPP waves with different polarization states, phase speeds, and attenuation rates can be excited. The use of a periodically nonhomogeneous semiconductor layer for excitation of multiple SPP waves with different polarization states, phase speeds, and attenuation rates can help enhance light absorption in thin-film solar cells.

CdTe and other thin-film polycrystalline solar cells have potential spatial non-uniformities in their photovoltaic response that can both lower their performance and complicate the analysis of their current-voltage curves. Polycrystalline cells have inherent non-uniformities associated with their grain structure, but there are a variety of other possibilities including thickness variations, local shunts, and weak-diode areas. Additionally, there are possible issues associated with the fabrication process due to cleaning residues, scratches, thermal variations, and particulate inclusions. The primary measurements described here to map the non-uniformities of CdTe cells are light-beam-induced current (LBIC), which gives a direct measure of the local PV response, and electroluminescence (EL), which is the inverse of the PV effect. The former is attractive, because it can be used to deduce the local current-voltage curve, but data collection is time consuming. The latter though the use of modern CCD cameras takes only a few seconds and is compatible with production-line screening.

The Hall effect is a primary method to measure carrier density, mobility and carrier type in semiconducting materials. Many contemporary semiconductor and electronic materials being developed for green energy, efficient lighting, flexible inexpensive electronics and high power devices are characterized by very low mobilities^1,2,3. For a traditional DC field Hall system, mobilities of less than 10 cm²/(Vs) become very difficult to measure with magnetic fields on the order of 1 T. This paper examines an AC field Hall measurement methodology that allows one to measure Hall mobilities down to 0.001 cm²/(Vs)-lower than possible using traditional DC field Hall measurement techniques. The first section of this paper is a review of the DC method, followed by the introduction of the AC method. AC field measurements of microcrystalline Si and ZnO are presented.

Various types of modules were installed on a outdoor test facility. IV-curves of all these modules are measured every ten minutes. Measured irradiation, module temperature and air mass are used for analysis and comparison of the IV-curves. The influence of the respective air mass was higher than expected. Different correction procedures have been compared. Best results are achieved when the data are selected in a small range of air mass and module temperature and corrected to the same irradiation. Modules of the same types like the outdoor exposed modules were stored without irradiation for some years. Afterwards, they were exposed at the outdoor test site together with the other modules. Comparison of the module data of the same type allows the investigation of the stabilisation behaviour of the modules directly.

In the paper the process of controlled formation of nanostructured silicon is demonstrated and the optical performance compared to standard and textured interfaces. The influence of the formation technique type on its structure, photoluminescent and anti-reflecting properties is studied. The layers of nanostructured silicon have been formed on the textured surface of solar cells. It has been demonstrated that the use of nanostructured silicon reduces the anti-reflection coefficient significantly. It is also shown, that the formation of nanostructured silicon on a textured substrate of singlecrystal silicon after formation on them of contact systems results in decrease of consecutive resistance, increase of short circuit current, decrease of shunting resistance and increase of efficiency.

Next-generation photovoltaic structures require well-established deposition routes to conformal and conducting materials with defined chemical, physical and electronic composition. This work reports on the preliminary findings associated with conformal metal oxides on structured substrates including: 1) Discovery of sputtering process conditions that can be made semi-conformal when combined with in-situ techniques such as ion-beam milling for honing surface structures; 2) Development of relevant ALD chemistries that are materials-properties competitive with sputtered materials; 3) Evaluation of chemically-functionalized surface structures that maximize surface area but are structurally tailored for efficient gas flow and to minimize line-of-sight shadowing. The initial experiments have centered on combinations of amorphous and crystalline indium oxide, zinc oxide, aluminum zinc oxide, indium tin oxide, fluorinated tin oxide and indium zinc oxide. This presentation will describe these initial experiments and elucidate key physiochemical nature of the deposited thin films.

Colloidal quantum dot solar cells offer the possibility of combining low-cost, low-temperature solution-processing with efficient photon harvesting over the entire solar spectrum. Their quantum size effect tunability offers a path to tandem and triple-junction cells. The first solution-processed infrared solar cells were reported in 2005; the latest devices offer greater than 5% AM1.5 PCE and many paths remain for further improvement to 10% and beyond. We will review the field and its prospects.

The fabrication of low-cost n-Si/p-AgGaSe₂ heterojunction solar cells by controlled thermal evaporation method is reported. It is observed that in the case of p-AgGaSe₂ films deposited on H-terminated n-Si (H-Si) substrates at higher temperature of 650K, the photovoltaic properties of the n-Si/p-AgGaSe₂ junctions are considerably improved. The improved junction, under solar simulator AM1 illumination, demonstrated an efficiency of ~5.2% on an active area of 0.18 cm² without any antireflection coating whereas the AgGaSe₂ films thermally evaporated at room temperature of 300K on H-Si substrates showed the efficiency ~2.1%.

The minority carrier transport length (L) is a critical parameter limiting the performance of inexpensive Cu2O-ZnO photovoltaic devices. In this work, this length is determined for electrochemically deposited Cu2O by linking the optical carrier generation profile from front and back incident-photon-to-electron conversion efficiency (IPCE) measurements to a one dimensional carrier transport model. A transport length of ~ 400 nm is estimated. This critical length explains the losses typically presented by these devices. The consequences of this L on device design with the aim of improving solar cell performance are described.

During the last eight years the manufacturing volume of thin film modules has grown at a compounded annualized rate of over 90%. Today the share of thin film products in the global photovoltaics (PV) market is in the range of 10-15%. Considering the fact that wafer Si technologies have achieved impressive cost reductions during the last few years, any increase in thin film market share during the next decade will require these technologies to aggressively drive for cost reductions through device efficiency improvements and utilization of lower cost manufacturing techniques. Electrochemical deposition or electrodeposition is an attractive low cost approach for the formation of thin film coatings. Such coatings have already found large scale applications in circuit board fabrication and integrated circuit manufacturing. In these applications, the electroplated layers are mainly used as passive components that carry electrical current. Application of electrodeposition techniques to thin film solar cell fabrication involves formation of semiconductor absorber layers that actively participate in power generation. This requirement brings along certain challenges that need to be overcome. In this paper we will present a review of work carried out for the application of electrodeposition techniques to the fabrication of CdTe and CIGS based solar cells and modules.

We describe thin film photovoltaic (PV) technologies that have been scaled in manufacturing, and contrast their attributes and how they impact the levelized cost of electricity (LCOE). The thin film PV technologies reviewed include cadmium telluride (CdTe), copper indium gallium selenide (CIGS), amorphous silicon (a-Si), and microcrystalline/amorphous silicon (μ/a-Si) produced by a variety of methods. The factors studied include conversion efficiency, energy yield under different lighting and environmental conditions, location dependence, tracked/fixed tilt differential performance, uptime, output degradation rate, failure rate, lifetime, module cost, balance of system (BOS) and inverter cost, installation cost, land cost, operation cost, maintenance cost and finance cost. These thin film PV technologies are compared with crystalline silicon, the most widely deployed PV technology.

This work presents the activities carried out at ITMA Materials Technology related to the building integration of thin film (TF) photovoltaics (PV). Three different approaches have been developed in order to achieve high efficient solar cells at low manufacturing costs: (i) a new route for manufacturing monolithical silicon based thin film solar cells on building materials, (ii) the use of metallic nanoparticles for light trapping (plasmonic effects and light scattering) and (iii) the luminescent sol-gel coating on glass for solar concentration. In the first case, amorphous silicon modules (single junction) have been successfully manufactured at lab scale on steel and commercial ceramic substrates with efficiencies of 5.4% and 4.0%, respectively. Promising initial attempts have been also made in ethylene tetrafluoroethylene (ETFE), a polymer with high potential in textile architecture. In a similar way, the development of nanotechnology based coatings (metallic nanoparticles and luminescent materials) represent the most innovative part of the work and some preliminary results are showed.

The selective removal of thin films along linear pattern for the serial connections of the cell is the issue addressed in this work. The two opposing cases of ultrafast absorption and of controlled thermal stress are investigated for their potentials in reaching a clean layer separation with sharp edges, to point out the optimal laser process for the different cell layers, that we think to be potentially superior with mechanical approaches.

Messy liquid adhesives, short work times, long cure times, difficult clean-up of stray adhesive - all of these are associated with liquid adhesives for bonding solar cells. Current adhesion methods have been in place since the '70s: mix a two-part liquid silicone adhesive, coat a portion of adhesive onto a section of substrate, place the cells in a vacuum bag and wait for the adhesive to cure. Alternatively, one can use a fairly complicated robotic procedure to apply adhesive then fix a cell down and, again, wait for the adhesive to cure. Some difficulties that need to be overcome include balancing the amount adhesive to spread out with the available worktime in order to get all the cells onto the substrate with good adhesion; controlling the bondline; ensuring that the adhesive cures correctly after application; and, finally, if there is any re-work, removing the part from the adhesive without damaging everything around it.

The acceptance of solar cells in the built environment is partly dependent on the appearance of the solar modules. One aspect in the appearance is color. In most cases a solar cell itself reflects either blue or no color and will appear blackish. For the blue solar cells it is possible to tune the antireflection layer in such a way that a different color is reflected. We propose a front-sheet covered with a stack of thin layers consisting of high and low refractive index materials deposited from sol-gel onto PET foil such that only a particular wavelength range is reflected. We show through modeling that by alternating layers consisting of low refractive index layer (silica (SiO₂) and high reflection layer (silica-titania 25 mol% SiO₂: 75 mol%TiO₂) on PET foil such color reflection can be achieved. In modeling exercises the influence of the number of layers, thickness variations and angle of incidence on the reflected color are predicted as well as an estimated influence on the module efficiency. We show that with a four layer stack we can reach chroma values of 60 for green and 40 for red color in the CIELCH system. In experimental results we achieve a peak reflection of 41.7% with a band width of 90 nm while transmission is more than 90% for the other parts of the spectrum.

Mechanically grooved silicon solar cells with buried contact copper electrode were attempted. In order to groove a simple mechanical grooving system was home-made, in which synchronous motors in hard disc driver (HDD), audio amplifier, signal generator were used. For the anti-reflection films sputtering condition for SiN_x films was optimized. With increasing input power, pressure, index of refraction of the films increased so that a very low etching rate of 0.8 nm/min could be achieved with a condition of Ar and N₂ flow rate of 5 SCCM, input power of 300 W and sputtering pressure of 1 × 10^-2 torr. Annealing condition for the formation of nickel silicie from electroless plated Ni-P layer was optimized as well as plating condition of copper electrode. However, the conversion efficiency of the BCSC in this study is 3.6% which is unexpectedly small. It seems that the reason for the low efficiency is due to short circuit forming in the lancet of the pyramid.

This study investigates the physical properties of Al-doped Mg_xZn_1-xO (AMZO) films. Al-doped Mg_xZn_1-xO films were deposited by radio-frequency (RF) magnetron sputtering system using a 4 inch ZnO/MgO/Al₂O₃ (76/19/5 wt%) target. This study determined the resulting x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS), Hall measurement, and transparent performance of the films. XRD results indicate that the diffraction angles of the annealed AMZO film shifted toward the high-angle side, indicating that thermal annealing could relax the compressive strain components in the as-deposited samples. XPS results reveal a high carbon content on the surface of Mg_xZn_1-xO. This may be due to contamination. The average Mg content of the as-grown AMZO is about 19.23 at. % at a depth of 40 nm. The Al-doped Mg_xZn_1-xO film in this study shows high transparency with transmittances over 95 % in the visible region (400 ~ 800nm), and a sharp absorption edge is visible in the UV region due to the Mg content. The Hall measurement of Al-doped Mg_xZn_1-xO films deposited at lower RF power show higher doping concentrations, lower resistivity and higher mobility as a function of the annealing temperature. Experimental results indicate that Al-doped Mg_xZn_1-xO film with 1000 °C annealing contains more oxygen vacancies, which play the role of donor. Oxygen vacancies generate states in the band gap and increase conductivity.

In this study, the influence of an active cell design on the power conversion efficiency (PCE) of a monolithic organic photovoltaic (OPV) module was investigated using experimental methods and circuit simulation. For circuit simulation using computer simulation-based study, the organic PV cell was described by a circuit-based two-diode model and the modules were simulated under several conditions including shading effect, diode model parameters, series resistance and shunt resistance, etc. A unit organic PV cell as a reference device and four types of monolithic organic PV modules with different active cell length were fabricated together on the same glass substrate. The characteristics of the fabricated unit OPV cell were measured and the electrical parameters were extracted to use them for the simulation of four types of monolithic organic PV modules. To analyze the influence of OPV cell design on the PCE of monolithic organic PV modules, the current-voltage (I-V) characteristic curves and the PCEs of the four type monolithic OPV modules with different active cell length were obtained and compared with the simulated results. The simulated I-V curves were matched well with the measured I-V curves for the four types of monolithic organic PV modules with different active cell length. The highest PCE of the monolithic OPV module was 2.86 % with the active cell length of 11.6 mm. We expect that this work is meaningful to enhance the performance of a monolithic OPV module to a certain extent and it offers a method to design a high-efficiency large-area monolithic OPV module.

Since CdS material has a direct and wide band-gap, it is very potential for fabricating photovoltaic devices. Due to its wide band-gap, CdS film can be acted as a window material to combine with Cu(In, Ga)Se₂ film. To obtain a quite uniform, easily scaling-up, and inexpensive sample, the CdS thin film with a thickness of 50 nm was deposited by using chemical bath deposition (CBD) technique. Through varying annealing temperatures and holding times, the electrical and optical properties of CdS film could be obviously improved. By Hall measurements, the carrier concentration of CdS sample S8 annealed at 100°C with 20 min is the maximum and its surface resistivity is the minimum. Summarizing these measuring data, we find that the concentration and the mobility of sample S8 are 2.4×10²¹ cm^-3 and 20.5 cm²/v-s, respectively, and it is very suitable for applying to Cu(In, Ga)Se₂-based solar cell.

In thin-film silicon photovoltaic modules the laser scribing processes are optimised to achieve low-loss performance of the segment interconnections. The characterisation of the component scribes and the contribution of the interconnect structure to the initial, degraded and low illumination performance of the module are described. Scribing processes based on nanosecond (ns) pulse duration lasers that are irradiated from the substrate side have been studied. These through-theglass (TTG) processes use selective laser wavelengths for targeted removal of the different layers in the photovoltaic cell structure. It is shown that wide process windows exist for the three laser scribing processes in the interconnect structure, with well defined behaviour at the limits of each process. In a second part of this paper, initial studies have been made on scribing processes using lasers with picosecond (ps) pulse durations with irradiation from the deposition layer side of the module. This 'top-scribe' approach allows a single wavelength for all three scribing processes and the high power ps laser sources now available can support scribe processing speeds of up to 120 m/min. The interaction between the ps laser and processed layers is characterised to derive the process ablation fluences and initial scribe process window parameters.