Optoelectrical analysis of TCO Silicon oxide double layers at the front and rear side of silicon heterojunction solar cells

Silicon Heterojunction has become a promising technology to substitute passivated emitter and rear contact PERC solar cells in pursuance of lower levelized cost of electricity through high efficiency devices. While high open circuit voltages and fill factors are reached, current loss related to the front and rear contacts, such as the transparent conductive oxide TCO layers is still a limiting factor to come closer to the efficiency limit of silicon based solar cells. Furthermore, reducing indium consumption for the TCO has become mandatory to push silicon heterojunction technology towards a terawatt scale production due to material scarcity and costs. To address these issues dielectric layers, such as silicon dioxide or nitride cappings are implemented to reduce TCO thicknesses both diminishing parasitic absorption and material consumption. However, reducing the TCO thickness comes in cost of resistive losses. Furthermore, the TCO properties do vary with thickness and neighboring layer configuration altering the optimization frame of the device. In this paper we present a detailed analysis to quantify the optoelectrical losses trade off associated to the TCO thickness reduction in such layer stacks. Through the analysis we show and explain why experimental bifacial cells with 20 nm front and rear TCO perform at a similar level to reference cells with 75 nm under front and rear illumination reaching efficiency close to 24 at 92 bifaciality. We present as well a simple interconnection method via screen printing metallization to implement a thin TCO silicon dioxide silver reflector enhancing current density from 39.6 to 40.4 mA cm2 without compromising resistive losses resulting in a 0.2 absolute solar cell efficiency increase from a bifacial design 23.5 23.7 . Finally, following this approach we present a certified champion cell with an efficiency of 24.

Electrochemical integration of graphene with light absorbing copper-based thin films

We present an electrochemical route for the integration of graphene with light sensitive copper-based alloys used in optoelectronic applications. Graphene grown using chemical vapor deposition (CVD) transferred to glass is found to be a robust substrate on which photoconductive Cu_{x}S films of 1-2 um thickness can be deposited. The effect of growth parameters on the morphology and photoconductivity of Cu_{x}S films is presented. Current-voltage characterization and photoconductivity decay experiments are performed with graphene as one contact and silver epoxy as the other

Evidence of PbI2 Containing Debris Upon P2 Nanosecond Laser Patterning of Perovskite Solar Cells

Laser based patterning for monolithic serial interconnection of metal halide perovskite MHP solar cells is a key process for industrial manufacturing of large scale MHP solar panels. It requires reliable patterning process parameters to achieve low interconnection losses and, thus, high efficiencies. Here, P2 laser patterning of the perovskite layer was obtained by laser ablation using conventional nanosecond laser pulses at systematically varied laser fluences. The correlation of the laser impact to the morphology, composition, and electrical functionality was analyzed in detail by several surface analytical techniques. The occurrence of laser induced periodic surface structures and microdroplets at the bottom of the trenches indicates that material removal via stress assisted ablation is strongly influenced by thermal processes. The formation of PbI 2 containing residuals was evidenced, possibly causing contact resistance losses through the P2 interconnect. These results contribute to the identification of loss factors in laser based serial interconnection of perovskite solar cells and to further process optimization for upscaling to industrial module size

In situ cell for grazing incidence x ray diffraction on thin films in thermal catalysis

A cell for synchrotron based grazing incidence x ray diffraction at ambient pressures and moderate temperatures in a controlled gas atmosphere is presented. The cell is suited for the in situ study of thin film samples under catalytically relevant conditions. To some extent, in addition to diffraction, the cell can be simultaneously applied for x ray reflectometry and fluorescence studies. Different domes enclosing the sample have been studied and selected to ensure minimum contribution to the diffraction patterns. The applicability of the cell is demonstrated using synchrotron radiation by monitoring structural changes of a 3 nm Pd thin film upon interaction with gas phase hydrogen and during acetylene semihydrogenation at 150 amp; 8201; C. The cell allows investigation of very thin films under catalytically relevant condition

Decay mechanisms in CdS buffered Cu In,Ga Se2 thin film solar cells after exposure to thermal stress Understanding the role of Na

Due to their tunable bandgap energy, Cu In,Ga Se2 CIGSe thin film solar cells are an attractive option for use as bottom devices in tandem configurations. In monolithic tandem devices, the thermal stability of the bottom device is paramount for reliable application. Ideally, it will permit the processing of a top device at the required optimum process temperature. Here, we investigate the degradation behavior of chemical bath deposited CBD CdS buffered CIGSe thin film solar cells with and without Na incorporation under thermal stress in ambient air and vacuum with the aim to gain a more detailed understanding of their degradation mechanisms. For the devices studied, we observe severe degradation after annealing at 300 C independent of the atmosphere. The electrical and compositional properties of the samples before and after a defined application of thermal stress are studied. In good agreement with literature reports, we find pronounced Cd diffusion into the CIGS absorber layer. In addition, for Na containing samples, the observed degradation can be mainly explained by the formation of Na induced acceptor states in the TCO front contact and a back contact barrier formation due to the out diffusion of Na. Supported by numerical device simulation using SCAPS 1D, various possible degradation models are discussed and correlated with our finding

Indium contamination from the indium-tin-oxide electrode in polymer light-emitting diodes

We have found that polymer light-emitting diodes (LEDs) contain high concentrations of metal impurities prior to operation. Narrow peaks in the electroluminescence spectrum unambiguously demonstrate the presence of atomic indium and aluminum. Rutherford backscattering spectroscopy (RBS) and x-ray photoelectron spectroscopy (XPS) depth profiling data corroborate this result. An average indium concentration of 5 x 10(19)atoms/cm(3) originating from the indium-tin-oxide (ITO) electrode has been found in the polymer layer. (C) 1996 American Institute of Physics

Laser based series interconnection of chalcopyrite und perovskite solar cells Analysis of material modifications and implications for achieving small dead area widths

Both nanosecond pulses and picosecond laser pulses are used for P2 patterning of chalcopyrite Cu In,Ga Se2, CIGSe and metal halide perovskite solar cell absorber layers. For CIGSe, the range of the modified material visualized by photoluminescence imaging is significantly wider than the actual physical linewidth, since energy input by the laser pulses leads to material modification in the vicinity of the scribed lines. This effect does not occur with the perovskite absorber layers, where there is no apparent influence on the edge regions. From numerical calculations of the temperature depth profiles and the surface temperature distributions it is concluded that this effect is due to the significantly lower perovskite absorber layer thickness compared to CIGSe and the nevertheless significantly higher laser fluence required for perovskite ablation. The unaffected edge regions around the P2 line in the perovskite enabled a reduction of the dead area width in the fabrication of 3 segmented mini modules, which could be significantly reduced from 430 to 230 m, while increasing the aperture area power conversion efficiency and also the geometric fill factor, which could be increased up to 94.

The challenge of studying perovskite solar cells stability with machine learning

Perovskite solar cells are the most dynamic emerging photovoltaic technology and attracts the attention of thousands of researchers worldwide. Recently, many of them are targeting device stability issues the key challenge for this technology which has resulted in the accumulation of a significant amount of data. The best example is the Perovskite Database Project, which also includes stability related metrics. From this database, we use data on 1,800 perovskite solar cells where device stability is reported and use Random Forest to identify and study the most important factors for cell stability. By applying the concept of learning curves, we find that the potential for improving the models performance by adding more data of the same quality is limited. However, a significant improvement can be made by increasing data quality by reporting more complete information on the performed experiments. Furthermore, we study an in house database with data on more than 1,000 solar cells, where the entire aging curve for each cell is available as opposed to stability metrics based on a single number. We show that the interpretation of aging experiments can strongly depend on the chosen stability metric, unnaturally favoring some cells over others. Therefore, choosing universal stability metrics is a critical question for future databases targeting this promising technolog

Reactor design for thin film catalyst activity characterization

Thin film based systems hold enormous potential for atomic scale control of catalysts and their supports. So far, there is only limited reactor design with dedicated characterization methods for such catalyst systems. Thus, this work focuses on designing and prototyping a tailored reactor to characterize thin films catalysts. Herein, an electrically driven reactor and its virtual replica are designed together in a way to measure and describe the reaction processes over thin film catalysts. The developed numerical model comprised of coupled fluid , thermal , and chemical reaction models in combination with the well defined geometry of the prototype allows a fast and comprehensive testing of novel catalysts systems, which is illustrated by acetylene hydrogenation with a palladium based thin film catalyst on silicon substrates as first model reaction. A power law model was found to be most appropriate to describe the kinetics of the corresponding reaction. It is shown that the codesigned virtual replica offers a strong platform for comprehensive testing and fairly accurate description of thin film catalysi