Akis, Richard | Search NASA

DOE OSTI2015

Diffusion-Reaction Modeling of Cu Migration in CdTe Solar Devices

In this work, we report on development of one-dimensional (1D) finite-difference and two-dimensional (2D) finite-element diffusion-reaction simulators to investigate mechanisms behind Cu-related metastabilities observed in CdTe solar cells [1]. The evolution of CdTe solar cells performance has been studied as a function of stress time in response to the evolution of associated acceptor and donor states. To achieve such capability, the simu-lators solve reaction-diffusion equations for the defect states in time-space domain self-consistently with the free carrier transport. Re-sults of 1-D and 2-D simulations have been compared to verify the accuracy of solutions.

Guo, Da↗

DOE OSTI2015

Self-consistent simulation of CdTe solar cells with active defects

We demonstrate a self-consistent numerical scheme for simulating an electronic device which contains active defects. As a specific case, we consider copper defects in cadmium telluride solar cells. The presence of copper has been shown experimentally to play a crucial role in predicting device performance. The primary source of this copper is migration away from the back contact during annealing, which likely occurs predominantly along grain boundaries. We introduce a mathematical scheme for simulating this effect in 2D and explain the numerical implementation of the system. Finally, we will give numerical results comparing our results to known 1D simulations to demonstrate the accuracy of the solver and then show results unique to the 2D case.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2014

One-Dimensional Reaction-Diffusion Simulation of Cu Migration in Polycrystalline CdTe Solar Cells

In this work, we report on developing 1D reaction-diffusion solver to understand the kinetics of p-type doping formation in CdTe absorbers and to shine some light on underlying causes of metastabilities observed in CdTe PV devices. Evolution of intrinsic and Cu-related defects in CdTe solar cell has been studied in time-space domain self-consistently with free carrier transport and Poisson equation. Resulting device performance was simulated as a function of Cu diffusion anneal time showing pronounced effect the evolution of associated acceptor and donor states can cause on device characteristics. Although 1D simulation has intrinsic limitations when applied to poly-crystalline films, the results suggest strong potential of the approach in better understanding of the performance and metastabilities of CdTe photovoltaic device.

14 SOLAR ENERGY↗

DOE OSTI2014

Extracting Cu Diffusion Parameters in Polycrystalline CdTe

It is well known that Cu plays an important role in CdTe solar cell performance as a dopant. In this work, a finite-difference method is developed and used to simulate Cu diffusion in CdTe solar cells. In the simulations, which are done on a two-dimensional (2D) domain, the CdTe is assumed to be polycrystal-line, with the individual grains separated by grain boundaries. When used to fit experimental Cu concentration data, bulk and grain boundary diffusion coefficients and activation energies for CdTe can be extracted. In the past, diffusion coefficients have been typically obtained by fitting data to simple functional forms of limited validity. By doing full simulations, the simplifying assumptions used in those analytical models are avoided and diffusion parameters can thus be determined more accurately.

14 SOLAR ENERGY↗

DOE OSTI2014

Book of Extended Abstracts IWCE 2014

It is well known that Cu plays an important role in CdTe solar cell performance as a dopant. In this work, a finitedifference method is developed and used to simulate Cu diffusion in CdTe solar cells. In the simulations, which are done on a twodimensional (2D) domain, the CdTe is assumed to be polycrystalline, with the individual grains separated by grain boundaries. When used to fit experimental Cu concentration data, bulk and grain boundary diffusion coefficients and activation energies for CdTe can be extracted. In the past, diffusion coefficients have been typically obtained by fitting data to simple functional forms of limited validity. By doing full simulations, the simplifying assumptions used in those analytical models are avoided and diffusion parameters can thus be determined more accurately.

14 SOLAR ENERGY↗

DOE OSTI2014

Book of Extended Abstracts IWCE 2014

In this work, we report on developing 1D reaction-diffusion solver to understand the kinetics of p-type doping formation in CdTe absorbers and to shine some light on underlying causes of metastabilities observed in CdTe PV devices. Evolution of intrinsic and Cu-related defects in CdTe solar cell has been studied in time-space domain self-consistently with free carrier transport and Poisson equation. Resulting device performance was simulated as a function of Cu diffusion anneal time showing pronounced effect the evolution of associated acceptor and donor states can cause on device characteristics. Although 1D simulation has intrinsic limitations when applied to poly-crystalline films, the results suggest strong potential of the approach in better understanding of the performance and metastabilities of CdTe photovoltaic device.

14 SOLAR ENERGY↗

DOE OSTI2014

Modeling Copper Diffusion in Polycrystalline CdTe Solar Cells

It is well known that Cu plays an important role in CdTe solar cell performance as a dopant. In this work, a finite-difference method is developed and used to simulate Cu diffusion in CdTe solar cells. In the simulations, which are done on a two-dimensional (2D) domain, the CdTe is assumed to be polycrystalline, with the individual grains separated by grain boundaries. When used to fit experimental Cu concentration data, bulk and grain boundary diffusion coefficients and activation energies for CdTe can be extracted. In the past, diffusion coefficients have been typically obtained by fitting data to simple functional forms of limited validity. By doing full simulations, the simplifying assumptions used in those analytical models are avoided and diffusion parameters can thus be determined more accurately

14 SOLAR ENERGY↗

DOE OSTI2014

CdTe Solar Cells: The Role of Copper

In this work, we report on developing 1D reaction-diffusion solver to understand the kinetics of p-type doping formation in CdTe absorbers and to shine some light on underlying causes of metastabilities observed in CdTe PV devices. Evolution of intrinsic and Cu-related defects in CdTe solar cell has been studied in time-space domain self-consistently with free carrier transport and Poisson equation. Resulting device performance was simulated as a function of Cu diffusion anneal time showing pronounced effect the evolution of associated acceptor and donor states can cause on device characteristics. Although 1D simulation has intrinsic limitations when applied to poly-crystalline films, the results suggest strong potential of the approach in better understanding of the performance and metastabilities of CdTe photovoltaic device.

14 SOLAR ENERGY↗

DOE OSTI2014

Cu Migration in Polycrystalline CdTe Solar Cells

An impurity reaction-diffusion model is applied to Cu defects and related intrinsic defects in polycrystalline CdTe for a better understanding of Cu’s role in the cell level reliability of CdTe PV devices. The simulation yields transient Cu distributions in polycrystalline CdTe during solar cell processing and stressing. Preliminary results for Cu migration using available diffusivity and solubility data show that Cu accumulates near the back contact, a phenomena that is commonly observed in devices after back-contact processing or stress conditions.

14 SOLAR ENERGY↗