Abstract
We have fabricated Cu2ZnSnSe4 (CZTSe) solar cells with different absorber layer thickness. Absorber layers with different thicknesses were fabricated by changing the thickness of e-beam evaporated Sn/Zn/Cu precursor stacks and then selenization in a rapid thermal processing system. Scanning electron microscopy revealed that by increasing the thickness the morphology of CZTSe films improves substantially and energy dispersive spectrometry measurements showed that the Cu to Sn ratio increased with increasing the film thickness, despite a similar Cu to Sn ratio in the starting layers. A longer minority carrier lifetime and higher open circuit voltage were achieved for solar cells with thicker absorber layers. A maximum conversion efficiency of 7.8% (without anti reflection coating) was achieved for a solar cell with 1.7μm thickness in which a low doping density of the order of 1015cm−3 was measured, leading to a wide space charge region of about 300nm.
Highlights
Kesterite compound Cu2ZnSn(S,Se)4, CZTSSe is being investigated as a promising candidate for cost effective thin film solar cells
3.1 Morphological analysis Top-view Scanning electron microscopy (SEM) images of CZTSe absorber layers with different thickness are shown in Fig.1.a to Fig.1.d and cross-sectional SEM images of devices with 700 nm and 1700 nm thickness are shown in Fig.1.e and Fig.1.f, respectively
Further improvement of Jsc of samples thicker than 1000 nm can be attributed to a wider Space Charge Region (SCR) that facilitate the collection of carriers
Summary
Kesterite compound Cu2ZnSn(S,Se)4, CZTSSe is being investigated as a promising candidate for cost effective thin film solar cells. CZTSe absorber layers with different thickness were fabricated by selenization of e-beam evaporated Sn, Zn and Cu layers.
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