This PDF file contains the front matter associated with SPIE Proceedings Volume 9936, including the Title Page, Copyright information, Table of Contents, Introduction (if any), and Conference Committee listing.

We developed finite element models of organic solar cells in order to investigate current pathways and dissipative losses under different geometries. The models are of purely resistive nature, as this is sufficient to describe the effects under consideration. The overall behaviour of the current mostly steers the resistive behaviour of the device and is a delicate consequence of the interplay between the individual layer properties, namely the resistivities and layer thicknesses in combination. The model calculations solely based on external material parameters, i.e. without fitting, yield the spatial distribution of the current densities, potentials and the according resistive losses. In particular, the current pathways are spread out from the entire length of the top contact towards the entire width of the ground contact, running along the electric potential gradient. On the other hand, current crowding appears at the foremost part of the top electrode, resulting in a respective concentration of the resistive loss in this vicinity. The resistive loss in turn is the origin of the heat pattern, which is visible in DLIT/ILIT experiments. The comparison between experiment and simulation shows remarkable agreement. Having established the description of defect free solar cells, defects were simulated. We utilized the micro-diode-model as another established simulation method to model shunt or blocking contact defects in combination with electro luminescence imaging methods. The respective heat patterns were calculated in FEM. Nice agreement is found between the various experimental and simulation methods. The respective heat patterns then allow identifying several classes of defects such as shunt defects or blocking contact defects in accordance with their patterns from various imaging measurements, bridging the gap between theory and experiment to further the detailed analysis of organic solar cells.

We report the synthesis of ultra-high aspect ratio copper nanowires (CuNW) and fabrication of CuNW-based transparent conductive electrodes (TCE) with high optical transmittance (>80%) and excellent sheet resistance (R_s <30 Ω/sq). These CuNW TCEs are subsequently hybridized with aluminum-doped zinc oxide (AZO) thin-film coatings, or platinum thin film coatings, or nickel thin-film coatings. Our hybrid transparent electrodes can replace indium tin oxide (ITO) films in dye-sensitized solar cells (DSSCs) as either anodes or cathodes. We highlight the challenges of integrating bare CuNWs into DSSCs, and demonstrate that hybridization renders the solar cell integrations feasible. The CuNW/AZO-based DSSCs have reasonably good open-circuit voltage (V_oc = 720 mV) and short-circuit current-density (J_sc = 0.96 mA/cm²), which are comparable to what is obtained with an ITO-based DSSC fabricated with a similar process. Our CuNW-Ni based DSSCs exhibit a good open-circuit voltage (V_oc = 782 mV) and a decent short-circuit current (J_sc = 3.96 mA/cm²), with roughly 1.5% optical-to-electrical conversion efficiency.

In this work are presented the results obtained with solar cells sensitized with quantum dots of cadmium sulphide (CdS) incorporating luminescent materials (NaYF4:Yb/Er). The study revealed that through using a bifunctional layer of NaYF4:Yb/Er submicron rods, the infrared radiation is absorbed in 980nm to generate luminescence in the visible region to 530nm, under the UP-conversion process, in the same way simultaneously, NaYF4:Yb/Er layer causes scattering toward the quantum dots, the emission and scattering generated by this material is reabsorbed by the QD-CdS, and these in turn are absorbing in its range of solar radiation absorption, Thus generates an increase in the electron injection into the semiconductor of TiO2. The results of a cell incorporating NaYF4: Yb/Er at 0.07M shown photoconversion efficiencies of 3.39% improving efficiency with respect to the reference solar cell without using NaYF4: Yb/Er of 1.99%. The obtained values of current and voltage showed a strong dependence of the percentage of NaYF4 Yb/Er, and the mechanism of incorporation of this material.

Thin films of Cu₂GeS₃ are grown by annealing copper layers in GeS and S gaseous atmosphere above 460°C. Below 500°C the cubic polymorph is formed, having inferior optoelectronic properties compared to the monoclinic phase, formed at higher temperature. The bandgap of the cubic phase lies below that of the monoclinic phase: they are determined from absorption measurements to be 1.23 and 1.55 eV respectively. Photoluminescence measurements are performed and only the monoclinic Cu₂GeS₃ shows a photoluminescence signal with a peak maximum at 1.57 eV. We attribute this difference between cubic and monoclinic to the higher quasi fermi level splitting of the monoclinic phase. Wavelength dependent photoelectrochemical measurements demonstrate the Cu₂GeS₃ to be p-type with an apparent quantum efficiency of less than 3 % above the band gap.

Optimizing the buffer layer in manufactured thin-film PV is essential to maximize device efficiency. Here, we describe a combined synthesis, characterization, and theory effort to design optimal buffers based on the (Cd,Zn)(O,S) alloy system for CIGS devices. Optimization of buffer composition and absorber/buffer interface properties in light of several competing requirements for maximum device efficiency were performed, along with process variations to control the film and interface quality. The most relevant buffer properties controlling performance include band gap, conduction band offset with absorber, dopability, interface quality, and film crystallinity. Control of an all-PVD deposition process enabled variation of buffer composition, crystallinity, doping, and quality of the absorber/buffer interface. Analytical electron microscopy was used to characterize the film composition and morphology, while hybrid density functional theory was used to predict optimal compositions and growth parameters based on computed material properties. Process variations were developed to produce layers with controlled crystallinity, varying from amorphous to fully epitaxial, depending primarily on oxygen content. Elemental intermixing between buffer and absorber, particularly involving Cd and Cu, also is controlled and significantly affects device performance. Secondary phase formation at the interface is observed for some conditions and may be detrimental depending on the morphology. Theoretical calculations suggest optimal composition ranges for the buffer based on a suite of computed properties and drive process optimizations connected with observed film properties. Prepared by LLNL under Contract DE-AC52-07NA27344.

CH₃NH₃PbI₃ perovskite solar cells are one of the most exciting technologies in the renewable energy field, resulting in over 20% power conversion efficiency. Deep understanding of the working principle is now required to turn the high efficiency solar cells into a reliable technology. In this work we have explored the role of deposition method on the crystallinity of perovskite films and its influence on the hysteresis behavior of the current-voltage characteristics. In addition Nb₂O₅ was used as hole blocking layer and its influence is also discussed. We have found that hysteresis is strongly dependent on both; perovskite deposition method and Nb₂O₅ thickness. The ideal condition where the hysteresis is suppressed or minimized was achieved by using the sequential deposition method for the perovskite semiconductor and a hole blocking layer of 50 nm.

Solution based perovskite solar cell fabrication typically involves rather complex processing sequences to yield highest performance. While most studies concentrate on the exploration of processing conditions, we have investigated the purity levels of common perovskite precursor solutions and found a number of impurities which are most critically controlling the crystallization of perovskites. Moreover, we identified these impurities at different level of concentrations is all commercially available precursors. In detail, we present a detailed chemical study on the nature of the various impurities in CH3NH3I and explored their impact on the crystal formation. The detrimental role of the impurities is best demonstrated by comparing perovskite solar cell devices fabricated from impurity free precursors vs precursors containing different concentrations of impurities. Most interestingly, we revealed that a certain concentration of impurities is detrimental to facilitate the growth of large grained crystals. This study gives valuable insight into the rate determining steps of perovskite crystal growth and provides the basis for developing reliable and reproducible high performance recipes for Perovskite solar cell processing.

Smooth, compact and defect free morphology of perovskite is highly desired for enhanced device performance. Several routes such as thermal annealing, use of solvent mixtures, growth under controlled humidity has been adopted to obtain crystalline, smooth and defect free perovskite film. Herein we showed direct use of water (H2O) as co-solvent in precursor solution and have optimized the water content required to obtain smooth and dense film. Varying concentration of water was used in precursor solution of CH3NH3I and PbI2 mixed in γ-butyrolactone (GBL) and dimethylsulfoxide (DMSO). Perovskite films were crystallized using toluene assisted solvent engineering method using GBL:DMSO:H2O as solvent mixture. The amount of water was varied from 1% to 25%, which resulted in change in film morphology and perovskite crystallinity. It was concluded that an appropriate amount of water is required to assist the crystallization process to obtain smooth pin-hole free morphology. The change in morphology led to improved fill factor in the device, with highest efficiency ~14%, which was significantly higher than devices made from perovskite film without adding water. We also showed that addition of up to 25% by volume of water does not significantly change the device performance.

While the development of perovskite-based semitransparent solar cells with competitive levels of transparency and efficiency offer a promising perspective towards building integrated photovoltaics, the color perception of perovskite films is of limited visual aesthetics, compromising their applicability to facades and windows. In the present work, we develop a technique to grow crystalline, ultrathin perovskite films through a solvent-solvent extraction process featuring full crystallization within few seconds at RT and under 45%RH environmental conditions. As a result we obtained the highest combination of efficiency and transparency to date for perovskite solar cells. We further improved the visual aesthetics of our devices by implementing dielectric mirrors. EQE and UV-Vis spectroscopic measurements are performed to fully characterize the device stacks featuring four different dielectric mirror configurations. By customizing the mirror to the near-IR absorption region of the perovskite, we could increase the Jsc by 18.7%, yielding a light blue appearance and showing 31.4% transparency at 3.5% electrical power efficiency. Both, the solar cells and the dielectric mirrors are fully-solution processed under ambient conditions and are easily transferable to roll-to-roll upscaling. Optical simulations support our experimental findings and provide a global perspective emulating full device stack appearance covering all the colors in the visible spectra. Transparency, photocurrent density contribution and chromaticity are finally simulated and analyzed. Based on the detailed analysis, we give an outlook on the performance – color – transparency roadmap for perovskite solar cells.

We report effects of controlled humidity in ambient condition on grain boundary potential and charge transport within the grains of Pervoskite films prepared by sequential deposited technique. Grain boundary exhibited variation of their electronic properties with change in humidity level from sample kept inside glove box to 75% RH. X-ray diffraction (XRD) indicates the formation of PbI2 phase with increasing humidity level. The degradation of Pervoskite solar cell is mainly associated with the increase of PbI2 phase with increase in humidity level and hydration of the grain boundaries with the formation of hydrated phases. Spatial mapping of surface potential in the Perovskite film exhibits higher positive potential at grain boundaries compared to the surface of the grains. Grain boundary potential barrier were found to increase from ~35 meV to 80 meV for perovskite film exposed to 75% RH level compared to perovskite film kept inside glove box. Nanoscale current sensing measurement (Cs-AFM) shows that charge transport in perovskit solar cell strongly depends in humidity level. Performances of the solar cell was maximum for 25% humidity with 14.01 %. Transient measurement shows decrease in charge carrier life time and charge transport time with increase in humidity level. Our results show strong correlation between humidity level, electronic grain boundary properties and device performance.

Design and simulation of a novel pressure microgripper based on Microelectromechanical, MEM technology, and composed by several electrothermal microactuators were carried out in order to increment the displacement and the cutoff force. The implementation of an element of press or gripping in the arrow of chevron actuator was implemented to supply stability in the manipulation of micro-objects. Each device of the microgripper and its fundamental equations will be described. The fundamental parameters to understand the operation and behaviour of the device are analyzed through sweeps of temperature (from 30 °C up to 100 °C) and voltage (from 0.25 V up to 5 V), showing the feasibility to operate the microgripper with electrical or thermal feeding. The design and simulation were development with Finite Element Method (FEM) in Ansys-Workbench 16.0. In this work, the fundamental parameters were calculated in Ansys-Workbench. It is shown, that structural modifications have great impact in the displacement and the cut-off force of the microgripper.

Recent reports indicate that thin films of oxides of zinc: ZnO, Zn(O,S), or Zn-Mg-O, could be a better buffer component than CdS to provide an adequate band alignment with orthorhombic tin sulphide in thin lm solar cells. Thin films of ZnO were grown by rf-magnetron sputtering on different substrates at room temperature. Thin films of ZnO obtained by different deposition methods show hexagonal crystal structure, usually with a preferential orientation of (002) crystallographic planes parallel to the substrate surface. However, in the present study XRD patterns indicate that thicker ZnO films on glass substrates have preferential growth of (103) planes, while that on chemically deposited CdS or ZnS films preferential orientation of (002) planes persists. Bandgap of ZnO films increases from 3.2 eV to 3.4 eV when the chamber pressure used for deposition varies from 2.3 mTorr to 6 mTorr. ZnO films were incorporated in a solar cell structure stainless steel/SnS(cubic)/SnS(orthorhombic)/SnS(cubic)/CdS/ZnO/ZnO:Al. It showed open-circuit voltage of 0.318 V, short-circuit current density of 3.6 mA/cm² and conversion efficiency of 0.82%.