This PDF file contains the front matter associated with SPIE Proceedings Volume 7771, including the Title Page, Copyright information, Table of Contents, Introduction, and the Conference Committee listing.

We report our progress in the optimization of Ag/ZnO back reflectors (BR) for a-Si:H and nc-Si:H solar cells. Theoretically, a BR with a smooth metal surface and a textured dielectric surface would be more desirable. A smooth metal/dielectric interface reduces the plasmonic resonance loss and parasitic losses due to light trapped in sharp angles; a textured dielectric/semiconductor interface provides scattering for light trapping. In order to obtain sufficient light scattering at the ZnO/silicon interface, a highly textured ZnO layer is normally used. However, a highly textured ZnO surface causes deterioration of nc-Si:H material quality. In addition, to make a highly textured ZnO surface, a thick ZnO layer is needed, which could introduce additional absorption in the bulk ZnO layer and reduce the photocurrent density. Therefore, Ag/ZnO BR structures for nc-Si:H solar cells needs to be optimized experimentally. In this study, we found that an optimized Ag/ZnO BR for nc-Si:H solar cells is constructed with textured Ag and thin ZnO layers. Although a textured Ag layer might cause certain losses resulting from plasmonic absorption, the enhanced light scattering by a moderately textured Ag layer makes it possible to use a thin ZnO layer, where the absorption in the ZnO layer is low. With such a BR, we achieved a short-circuit current density of over 29 mA/cm² from a nc-Si:H single-junction solar cell. Using the high performance nc-Si:H cell in an a-Si:H/nc- Si:H/nc-Si:H triple-junction structure, we achieved an initial active-area efficiency of 14.5% with a total current density exceeding 30 mA/cm2.

Solar modules made from thin-film crystalline-silicon layers of high quality on glass substrates could lower the price of photovoltaic electricity substantially. Almost half of the price of wafer-based silicon solar modules is currently due to the cost of the silicon wafers themselves. Using crystalline-silicon thin-film as the active material would substantially reduce the silicon consumption while still ensuring a high cell-efficiency potential and a stable cell performance. One way to create a crystalline-silicon thin film on glass is by using a seed layer approach in which a thin crystalline-silicon layer is first created on a non-silicon substrate, followed by epitaxial thickening of this layer. In this paper, we present new solar cell results obtained on 10-micron thick monocrystalline-silicon layers, made by epitaxial thickening of thin seed layers on transparent glass-ceramic substrates. We used thin (001)-oriented silicon single-crystal seed layers on glass-ceramic substrates provided by Corning Inc. that are made by a process based on anodic bonding and implant-induced separation. Epitaxial thickening of these seed layers was realized in an atmospheric-pressure chemical vapor deposition system. Simple solar cell structures in substrate configuration were made from the epitaxial mono-silicon layers. The Si surface was plasma-textured to reduce the front-side reflection. No other light trapping features were incorporated. Efficiencies of up to 11% were reached with Voc values above 600 mV indicating the good electronic quality of the material. We believe that by further optimizing the material quality and by integrating an efficient light trapping scheme, the efficiency potential of these single-crystal silicon thin films on glass-ceramics should be higher than 15%.

A new laser scribing scheme for poly-Si based thin film solar cell is proposed. This technology consists of 1) simultaneous removal of underlying TCO and poly-Si film, 2) electrical isolation by resin coating using inkjet and 3)selective top electrode removal by laser ablation of photoresist mask layer followed by chemical etching. Process defects such as crack and parasitic melting can be eliminated by proposed patterning technology. This process can be highly cost-effective because less laser patterning steps are required and less area for series interconnection is needed. Poly-Si thin film solar cell was successfully fabricated and showed 7.4% of conversion efficiency.

Stabilized performance parameters of PV-modules are necessary for energy yield prediction as well as for the investigation of module degradation effects. The electrical parameters of thin-film modules show stabilization behaviors which are typical for the applied technology. However, this behavior is not satisfyingly understood yet. Different types of thin-film modules have been exposed to artificial irradiation and controlled temperatures in a climatic cabinet with a class B solar simulator for up to 330h. The modules have been connected to electronic loads to perform IV-curve measurements every 15 minutes and MPP-tracking between the measurements. The stabilization of the different parameters (Uoc, Isc, FF, Pmpp) has been analyzed using this data. Temperature correction was done with temperature coefficients which have been measured after a certain irradiation dose had been applied. Flasher-measurements have been used for confirmation of the DC-measurements after the relaxation of the modules after the continuous irradiation exposure was finished.

In recent years it has become common practice to texture many of the layered surfaces making up photovoltaic cells in order to increase light absorption and efficiency. Profilometry has been used to characterize the texture, but this is not satisfactory for in-line production systems which move surfaces too fast for that measurement. Scatterometry has been used successfully to measure roughness for many years. Its advantages include low cost, non-contact measurement and insensitivity to vibration; however, it also has some limitations. This paper presents scatter measurements made on a number of photovoltaic samples using two different scatterometers. It becomes clear that in many cases the surface roughness exceeds the optical smoothness limit (required to calculate surface statistics from scatter), but it is also clear that scatter measurement is a fast, sensitive indicator of texture and can be used to monitor whether design specifications are being met. A third key point is that there is a lot of surface dependent information available in the angular variations of the measured scatter. When the surface is inspected by integrating the scatter signal (often called a "Haze" measurement) this information is lost.

Conventional patterning processes for series connection of silicon thin film solar cells are composed of laser scribing processes, such as pattering of front electrode (P1), patterning of silicon thin films (P2) and patterning of silicon thin films and back electrode (P3). However, we have proposed a new series connection scheme of silicon thin film solar cells using direct inkjet patterning technology. The combination of laser scribing and inkjet printing technologies can realize the series connected cell structure. After the deposition of silicon thin films without P1 process, both front electrode and silicon thin films are patterned first by ultra violet (UV) laser scribing with the wavelength of 352 nm. Then, to prevent the shunting between front and back electrodes, spacers were formed on the sidewalls of laser scribed lines by inkjet printing. The series connected cells were fabricated by the following deposition of back electrode and P3 laser scribing process. In this research, we have developed the spacer formation process using the resin based dielectric ink. Also, we have fabricated and characterized the amorphous silicon (a-Si) thin film solar modules with proposed structure.

As advancements thin-film and flexible electronics like printed organic solar cells and organic LEDs bring these devices close to market entry new processing technologies for cost-effective, high quality production have to be developed. Laser technology provides a huge potential to fulfill the demanding tasks that come with the transition from lab to factory. 3D-Micromac looked into the possibilities of ultra-short pulsed lasers for scribing of transparent conductive layers as well as active layers of organic solar cells. This paper presents the results of this research.

This study investigated the relationship of anthocyanin concentration from different organic fruit species and output voltage and current in a TiO2 dye-sensitized solar cell (DSSC) and hypothesized that fruits with greater anthocyanin concentration produce higher maximum power point (MPP) which would lead to higher current and voltage. Anthocyanin dye solution was made with crushing of a group of fresh fruits with different anthocyanin content in 2 mL of de-ionized water and filtration. Using these test fruit dyes, multiple DSSCs were assembled such that light enters through the TiO2 side of the cell. The full current-voltage (I-V) co-variations were measured using a 500 Ω potentiometer as a variable load. Point-by point current and voltage data pairs were measured at various incremental resistance values. The maximum power point (MPP) generated by the solar cell was defined as a dependent variable and the anthocyanin concentration in the fruit used in the DSSC as the independent variable. A regression model was used to investigate the linear relationship between study variables. Regression analysis showed a significant linear relationship between MPP and anthocyanin concentration with a p-value of 0.007. Fruits like blueberry and black raspberry with the highest anthocyanin content generated higher MPP. In a DSSC, a linear model may predict MPP based on the anthocyanin concentration. This model is the first step to find organic anthocyanin sources in the nature with the highest dye concentration to generate energy.

We describe the production of photovoltaic modules with high-quality large-grain copper indium gallium selenide (CIGS) thin films obtained with the unique combination of low-cost ink-based precursors and a reactive transfer printing method. The proprietary metal-organic inks contain a variety of soluble Cu-, In- and Ga- multinary selenide materials; they are called metal-organic decomposition (MOD) precursors, as they are designed to decompose into the desired precursors. Reactive transfer is a two-stage process that produces CIGS through the chemical reaction between two separate precursor films, one deposited on the substrate and the other on a printing plate in the first stage. In the second stage, these precursors are rapidly reacted together under pressure in the presence of heat. The use of two independent thin films provides the benefits of independent composition and flexible deposition technique optimization, and eliminates pre-reaction prior to the synthesis of CIGS. In a few minutes, the process produces high quality CIGS films, with large grains on the order of several microns, and preferred crystallographic orientation, as confirmed by compositional and structural analysis by XRF, SIMS, SEM and XRD. Cell efficiencies of 14% and module efficiencies of 12% were achieved using this method. The atmospheric deposition processes include slot die extrusion coating, ultrasonic atomization spraying, pneumatic atomization spraying, inkjet printing, direct writing, and screen printing, and provide low capital equipment cost, low thermal budget, and high throughput.

Based on Crosslight APSYS, single junction ZnTe/CdSe, CdZnTe/CdSe and CIGS/CdS solar cells as well as CdZnTe(CdSe)/CIGS tandem cells are modeled. Basic physical quantities like band diagrams, optical absorption and generation are obtained. Quantum efficiency and I-V curves are presented. The results are discussed with respect to the interface recombination velocity and the related material defect trap states for ZnTe/CdSe single junction solar cells and the top TCO layer affinity for tandem cells. The projected efficiency obtained is 28% for one of the modeled twoterminal tandem cells. The modeling results give possible clues for developing CdZnTe(CdSe)/CIGS tandem solar cells with increased efficiency.

In recent years, thin-film photovoltaic (PV) companies started realizing their low manufacturing cost potential, and grabbing an increasingly larger market share from multicrystalline silicon companies. Copper Indium Gallium Selenide (CIGS) is the most promising thin-film PV material, having demonstrated the highest energy conversion efficiency in both cells and modules. However, most CIGS manufacturers still face the challenge of delivering a reliable and rapid manufacturing process that can scale effectively and deliver on the promise of this material system. HelioVolt has developed a reactive transfer process for CIGS absorber formation that has the benefits of good compositional control, high-quality CIGS grains, and a fast reaction. The reactive transfer process is a two stage CIGS fabrication method. Precursor films are deposited onto substrates and reusable print plates in the first stage, while in the second stage, the CIGS layer is formed by rapid heating with Se confinement. High quality CIGS films with large grains were produced on a full-scale manufacturing line, and resulted in high-efficiency large-form-factor modules. With 14% cell efficiency and 12% module efficiency, HelioVolt started to commercialize the process on its first production line with 20 MW nameplate capacity.

NREL CIGS devices with up to 20% efficiency are prepared using a three-stage process for the CIGS layer with the last step of an intrinsic ZnO and conductive ZnO:Al bilayer. This work outlines the efficiency and performance parameters for these CIGs devices when this bilayer is replaced with indium zinc oxide (a-InZnO), an amorphous metal oxide. It is well known that metal oxides can serve a variety of important functions in thin film photovoltaics such as transparent electrical contacts (TCO's), antireflection coatings and chemical barriers. In the case of a-InZnO, we have reported on the determination of the relative roles of metals and oxygen stoichiometries on the opto-electronic properties of a-InZnO thin films as well as the stability of those films in damp heat. Since InZO has a tunable conductivity based on the amount of oxygen introduced during deposition, it can be used as both the intrinsic and TCO layers. We were able to establish preliminary metrics for an all InZnO bilayer whose performance was comparable to a common CIGs device.

Normally, CdS film is used as the buffer layer in the fabrication of copper indium gallium selenide solar cells. These solar cells can reach an efficiency of 10.3% when produced by a non-vacuum process. However, this is a very toxic process. In this study, we propose using a nontoxic zinc sulfide (ZnS) buffer layer which is deposited by chemical bath deposition. It took only 15 minutes to reach a ZnS thickness of 50nm and the transmittance of the finished device was higher than 80%. The back contact of the Mo layer sheet resistivity is 0.22 (Ω/square). The precursor solution for the cell fabrication was prepared from anhydrous hydrazine. The film was then deposited by spraying and finally heated rapidly to 520 without external selenization.

Metallic tapes are used to reliably connect CIGS thin-film solar panels to the junction box. Compared to soldering and gluing, ultrasonically bonding these tapes offers several benefits: a room-temperature process, lower consumable cost, stronger and more reliable bonds, and lower contact resistance. A MoSe₂ layer can form on the back contact Mo layer during the CIGS selenization. The thickness of the MoSe₂ layer varies with the details of the deposition and selenization process. MoSe₂ is a solid lubricant that creates a low friction interface between the tape and Mo layer, thus reducing ultrasonic coupling and making ultrasonic bonding more challenging. MoSe₂ also has a volume resistivity about 3,500 times higher than Mo. Its presence increases the tape contact resistance and thus reduces the efficiency of the solar module. It is therefore desired to remove the MoSe2 layer to make a reliable connection. Several processes were investigated on samples with varying MoSe₂ layer thickness. The effectiveness of those processes was studied and evaluated by using Scanning Electron Microscope (SEM), Energy Dispersive X-ray Analysis (EDAX), 90° bond peel test, and electrical contact resistance measurements. Complete removal of the MoSe2 layer without damaging the Mo layer underneath was successfully achieved. Strong bonds with more than 900g peel force for 2.00mm (width) × 0.10mm (thickness) Aluminum tapes and a low contact resistivity of <1.5 mΩcm2 were consistently demonstrated.