Effect of gallium grading in Cu(In,Ga)Se2 solar-cell absorbers produced by multi-stage coevaporation

• We investigate Cu(In,Ga)Se2 thin films grown in multi-stage coevaporation processes and solar cells fabricated from such absorbers. Despite some interdiffusion during film growth, Ga/(Ga+In) gradients defined via evaporation-profile variations in the process are to a good part retained in the finished film. This indicates that the bandgap can be engineered in this type of process by varying the evaporation profiles, and consequently also that unintended profile variations should be noted and avoided. With front-side gradients the topmost part of many grains seems to be affected by a higher density of lattice defects due to the strong change of gallium content under copper-poor growth conditions. Electrically, both back-side gradients and moderate front-side gradients are shown to yield an improvement of device efficiency. If a front-side gradient is too wide, though, it causes strong voltage-dependent collection and the fill factor is severely reduced.

Ämnesord

NATURVETENSKAP  -- Fysik (hsv//swe)

NATURAL SCIENCES  -- Physical Sciences (hsv//eng)

Nyckelord

CIGS

Coevaporation

Multi-stage process

Three-stage process

Gradients

Physics

Fysik

TECHNOLOGY

TEKNIKVETENSKAP

Teknisk fysik med inriktning mot elektronik

Engineering Science with specialization in Electronics

Teknisk fysik med inriktning mot materialvetenskap

Engineering Science with specialization in Materials Science

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