Electrostatic potentials at Cu In,Ga Se2 grain boundaries Experiment and simulations

In the present Letter, we report on a combined ab initio density functional theory calculation, multislice simulation, and electron holography study, performed on a amp; 931;9 grain boundary GB in a CuGaSe2 bicrystal, which exhibits a lower symmetry compared with highly symmetric amp; 931; 3 GBs. We find an electrostatic potential well at the amp; 931;9 GB of 0.8 V in depth and 1.3 nm in width, which in comparison with results from amp; 931;3 and random GBs exhibits the trend of increasing potential well depths with lower symmetry. The presence of this potential well at the amp; 931; 9 GB can be explained conclusively by a reduced density of atoms at the GB. Considering experimental limitations in resolution, we demonstrate quantitative agreement of experiment and theor

Light Induced Increase of Electron Diffusion Length in a p n Junction Type CH3NH3PbBr3 Perovskite Solar Cell

High band gap, high open circuit voltage solar cells with methylammonium lead tribromide MAPbBr3 perovskite absorbers are of interest for spectral splitting and photoelectrochemical applications, because of their good performance and ease of processing. The physical origin of high performance in these and similar perovskite based devices remains only partially understood. Using cross sectional electron beaminduced current EBIC measurements, we find an increase in carrier diffusion length in MAPbBr3 Cl based solar cells upon low intensity a few percent of 1 sun intensity blue laser illumination. Comparing dark and illuminated conditions, the minority carrier electron diffusion length increases about 3.5 times from Ln 100 50 nm to 360 22 nm. The EBIC cross section profile indicates a p amp; 8722;n structure between the n FTO TiO2 and p perovskite, rather than the p amp; 8722;i amp; 8722;n structure, reported for the iodide derivative. On the basis of the variation in space charge region width with varying bias, measured by EBIC and capacitance amp; 8722;voltage measurements, we estimate the net doping concentration in MAPbBr3 Cl to be 3 amp; 8722;6 1017 cm amp; 8722;

Correlative microscopy analyses of thin film solar cells at multiple scales

In the present work, a brief overview is given on how to apply transmission TEM as well as scanning electron microscopy SEM and their related techniques electron diffraction, energy dispersive X ray spectrometry, electron energy loss spectroscopy, electron holography; electron backscatter diffraction, electron beam induced current, cathodoluminescence for the analysis of interfaces between individual layers or extended structural defects in a thin amp; 64257;lm stack. All examples given in the present work were recorded on Cu In, Ga Se2 thin amp; 64257;lm solar cells, however, the shown experimental approaches may be used on any similar thin amp; 64257;lm semiconductor device. A particular aspect is the application of various techniques on the same identical specimen area, in order to enhance the insight into structural, com positional, and electrical properties. For aberration corrected TEM, the spatial resolutions of such measurements can be as low as on the subnanometer scale. However, when dealing with semiconductor devices, it is often necessary to characterize electrical and optoelectronic properties at larger scales, of few 10 nm up to even mm, for which SEM is more appropriate. At the same time, these larger scales provide also enhanced statistics of the analysis. In the present review, it is also outlined how to apply SEM techniques in combination with scanning probe and optical microscopy, on the same identical positions. Altogether, a multiscale toolbox is provided for the thorough analysis of structure property relationships in thin amp; 64257;lm solar cells using correlative microscopy approache

CdS/Cu(In,Ga)S2 based solar cells with efficiencies reaching 12.9% prepared by a rapid thermal process

In this letter, we report externally confirmed total area efficiencies reaching up to 12.9% for CdS/Cu(In,Ga)S2 based solar cells. These are the highest externally confirmed efficiencies for such cells. The absorbers were prepared from sputtered metals subsequently sulfurized using rapid thermal processing in sulfur vapor. Structural, compositional, and electrical properties of one of these champion cells are presented. The correlation between the Ga distribution profile and solar cell properties is discussed

Electron-beam-induced current at absorber back surfaces of Cu (In,Ga) Se2 thin-film solar cells

The following article appeared in Journal of Applied Physics 115.1 (2014): 014504 and may be found at http://scitation.aip.org/content/aip/journal/jap/115/1/10.1063/1.4858393The present work reports on investigations of the influence of the microstructure on electronic properties of Cu(In,Ga)Se2 (CIGSe) thin-film solar cells. For this purpose, ZnO/CdS/CIGSe stacks of these solar cells were lifted off the Mo-coated glass substrates. The exposed CIGSe backsides of these stacks were investigated by means of electron-beam-induced current (EBIC) and cathodoluminescence (CL) measurements as well as by electron backscattered diffraction (EBSD). EBIC and CL profiles across grain boundaries (GBs), which were identified by EBSD, do not show any significant changes at Σ3 GBs. Across non-Σ3 GBs, on the other hand, the CL signals exhibit local minima with varying peak values, while by means of EBIC, decreased and also increased short-circuit current values are measured. Overall, EBIC and CL signals change across non-Σ3 GBs always differently. This complex situation was found in various CIGSe thin films with different [Ga]/([In]+[Ga]) and [Cu]/([In]+[Ga]) ratios. A part of the EBIC profiles exhibiting reduced signals across non-Σ3 GBs can be approximated by a simple model based on diffusion of generated charge carriers to the GBs.This work was supported in part by the BMU projects comCIGS and comCIGSII. R.C. acknowledges financial support from Spanish MINECO within the program Ramon y Cajal (RYC-2011-08521)

Impact of dislocations and dangling bond defects on the electrical performance of crystalline silicon thin films

A wide variety of liquid and solid phase crystallized silicon films are investigated in order to determine the performance limiting defect types in crystalline silicon thin-film solar cells. Complementary characterization methods, such as electron spin resonance, photoluminescence, and electron microscopy, yield the densities of dangling bond defects and dislocations which are correlated with the electronic material quality in terms of solar cell open circuit voltage. The results indicate that the strongly differing performance of small-grained solid and large-grain liquid phase crystallized silicon can be explained by intra-grain defects like dislocations rather than grain boundary dangling bonds. A numerical model is developed containing both defect types, dislocations and dangling bonds, describing the experimental results

Grain boundaries in polycrystalline materials for energy applications: First principles modeling and electron microscopy

\ua9 2024 Author(s). Polycrystalline materials are ubiquitous in technology, and grain boundaries have long been known to affect materials properties and performance. First principles materials modeling and electron microscopy methods are powerful and highly complementary for investigating the atomic scale structure and properties of grain boundaries. In this review, we provide an introduction to key concepts and approaches for investigating grain boundaries using these methods. We also provide a number of case studies providing examples of their application to understand the impact of grain boundaries for a range of energy materials. Most of the materials presented are of interest for photovoltaic and photoelectrochemical applications and so we include a more in depth discussion of how modeling and electron microscopy can be employed to understand the impact of grain boundaries on the behavior of photoexcited electrons and holes (including carrier transport and recombination). However, we also include discussion of materials relevant to rechargeable batteries as another important class of materials for energy applications. We conclude the review with a discussion of outstanding challenges in the field and the exciting prospects for progress in the coming years

Point defect segregation and its role in the detrimental nature of Frank partials in Cu(In,Ga)Se2 thin-film absorbers

The interaction of point defects with extrinsic Frank loops in the photovoltaic absorber material Cu(In,Ga)Se₂ was studied by aberration-corrected scanning transmission electron microscopy in combination with electron energy-loss spectroscopy and calculations based on density-functional theory. We find that Cu accumulation occurs outside of the dislocation cores bounding the stacking fault due to strain-induced preferential formation of Cu‾²In, which can be considered a harmful hole trap in Cu(In,Ga)Se₂. In the core region of the cation-containing α-core, Cu is found in excess. The calculations reveal that this is because Cu on In-sites is lowering the energy of this dislocation core. Within the Se-containing β-core, in contrast, only a small excess of Cu is observed, which is explained by the fact that Cu¡ⁿ and Cu¡ are the preferred defects inside this core, but their formation energies are positive. The decoration of both cores induces deep defect states, which enhance nonradiative recombination. Thus, the annihilation of Frank loops during the Cu(In,Ga)Se₂ growth is essential in order to obtain absorbers with high conversion efficiencies