Zn(O,S) Buffer Layers and Thickness Variations of CdS Buffer for Cu2ZnSnS4 Solar Cells

• To improve the conduction band alignment and explore the influence of the buffer-absorber interface, we here investigate an alternative buffer for Cu2ZnSnS4 (CZTS) solar cells. The Zn(O, S) system was chosen since the optimum conduction band alignment with CZTS is predicted to be achievable, by varying oxygen to sulfur ratio. Several sulfur to oxygen ratios were evaluated to find an appropriate conduction band offset. There is a clear trend in open-circuit voltage Voc, with the highest values for the most sulfur rich buffer, before going to the blocking ZnS, whereas the fill factor peaks at a lower S content. The best alternative buffer cell in this series had an efficiency of 4.6% and the best CdS reference gave 7.3%. Extrapolating Voc values to 0 K gave activation energies well below the expected bandgap of 1.5 eV for CZTS, which indicate that recombination at the interface is dominating. However, it is clear that the values are affected by the change of buffer composition and that increasing sulfur content of the Zn(O, S) increases the activation energy for recombination. A series with varying CdS buffer thickness showed the expected behavior for short wavelengths in quantum efficiency measurements but the final variation in efficiency was small.

Ämnesord

TEKNIK OCH TEKNOLOGIER  -- Elektroteknik och elektronik -- Annan elektroteknik och elektronik (hsv//swe)

ENGINEERING AND TECHNOLOGY  -- Electrical Engineering, Electronic Engineering, Information Engineering -- Other Electrical Engineering, Electronic Engineering, Information Engineering (hsv//eng)

Nyckelord

Cu2ZnSnS4

CZTS

Current-voltage characteristics

Zn(O

S) buffer

kesterite photovoltaic cells

Teknisk fysik med inriktning mot elektronik

Engineering Science with specialization in Electronics

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