Potassium (K) post treatment on CIGSSe has been shown to yield the highest efficiency reported to date. However very little is known on the effect of K doping in CZTSSe and the mechanism behind the efficiency improvement. Here we reveal the mechanism by which K enhances the charge separation in CZTSSe. We show that K accumulates at the CdS/CZTSSe, passivating the recombination at front interface and improve carrier collection.
K is also found to accumulate at the CZTSSe/Mo interface and facilitates the diffusion of Cd into the absorber which affects the morphology and grain growth of CZTSSe. As revealed by the C-V, EQE and color J-V test, K doping significantly increases the carrier density, improves carrier collection, passivates the front interface and grain boundaries, leading to the enhancement of Voc and Jsc.
The average power conversion efficiency (PCE) has been promoted from 5% to above 7% and the best 7.78% efficiency has been achieved for the 1.5 mol% K-doped CZTSSe device. This work offers some new insights into the K doping effects on CZTSSe via solution based approach and demonstrates the potential of facile control of K doping for further improvement of CZTSSe thin film solar cells. Revealing the Role of Potassium Treatment in CZTSSe Thin Film Solar Cells.
Li, W., Su, Z., Tan, J.M.R., Chiam, S.Y., Seng, H.L., Magdassi, S. and Wong, L.H., 2017. Revealing the Role of Potassium Treatment in CZTSSe Thin Film Solar Cells. Chemistry of Materials, 29(10), pp.4273-4281.
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