Dresden 2017 – scientific programme

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HL: Fachverband Halbleiterphysik

HL 8: Photovoltaics

HL 8.4: Talk

Monday, March 20, 2017, 10:15–10:30, POT 251

First-principles modeling the alkali-metal post-deposition treatment of CIGS solar cells — •Maria Fedina, Hannu-Pekka Komsa, Ville Havu, and Martti Puska — Department of Applied Physics, Aalto University, P.O. Box 11000, Espoo, Finland

The efficiency of the Cu(In,Ga)Se₂ (CIGS) solar cell has increased significantly during the last few years thanks to the post-deposition treatment (PDT) by alkali metals. The PDT process results in formation of alkali metal impurities inside the CIGS grain interiors (GIs) and near grain boundaries (GB) We have calculated formation energies and migration barriers for Li, Na, K, Rb, and Cs impurities in bulk CuInSe₂ (CIS) within the framework of the density-functional theory. We will discuss the interplay between the alkali metal impurities and the native point defects in CIS. Moreover, the most important parameters of the secondary phases, such as lattice constants, band gaps, and heats of formation have been calculated. Mechanisms for secondary phase formation in CIGS will be discussed. Due to low free energies at surfaces and GBs, alkali metal atoms accumulate preferably at GBs and near the CIGS surface resulting in possible formation of secondary phases. We have calculated formation energies of alkali metal impurities also near different types of GBs and close to the surface, and we will discuss the prominent trends between different alkali metal atoms.