Relevance of Ge incorporation to control the physical behaviour of point defects in kesterite

Abstract

To reduce the prominent VOC-deficit that limits kesterite-based solar cells efficiencies, Ge has been proposed over the recent years with encouraging results, as the reduction of the non-radiative recombination rate...

Small Atom Doping: A Synergistic Strategy to Reduce SnZn Recombination Center Concentration in Cu2ZnSnSe4

“…Consequently, Zn vacancies are less stable in CZTSe as compared with cation antisites (i.e., Zn vacancies always show a higher formation energy than Cu Zn and Sn Zn ), explaining the proliferation of Cu Zn and Sn Zn defects, as described in Figure 7 (top). [ 73 ] By the end of the high‐temperature step, all Zn has been incorporated. However, Cu and Sn atoms remain at Zn positions, while Zn atoms occupy Cu and Sn sites.…”

“…[72] It is worth mentioning that Cu-rich conditions increase the single-phase CZTSe window, justifying why the compositional change from Cu-rich to Cupoor conditions has been successful. [73,74] However, Zn-rich compositions during growth are not easy to achieve due to the high stability of ZnSe. [23] In addition, reducing the Sn concentration in order to prevent Sn antisites is not a viable approach due to secondary phase formation (CuSe and Cu 2 Se) which would have a strong detrimental effect in the device properties.…”

Ge-alloyed kesterite thin-film solar cells: previous investigations and current status – a comprehensive review

“…Theoretically, Ge inclusion is expected to mainly counteract two loss mechanisms greatly affecting kesterite absorbers, namely defect-assisted recombination and band tailing, partly through the replacement of detrimental Sn 2+ species. 20,[24][25][26] Simultaneously, this strategy should improve PV-related characteristics and allow bandgap tuning, 27,28 which is particularly interesting for band alignment optimization. On top of this, experimental studies discussed herein demonstrate that integrating Ge into kesterites also enhances crystalline morphology by mitigating secondary phase formation.…”

Cd‐Free Pure Sulfide Kesterite Cu2ZnSnS4 Solar Cell with Over 800 mV Open‐Circuit Voltage Enabled by Phase Evolution Intervention

“…[14,15] For the performance-killing defect Sn Zn , first-principal calculations suggest that doping Ge in CZTS forms a more benign Ge Zn defect. [12,16] Despite also having deep energy levels, Ge Zn is less prevalent or detrimental due to its elevated formation energy and reduced carrier capture crosssection compared with Sn Zn . Therefore, Ge doping should be a feasible approach to alleviate nonradiative recombination and the V OC deficit.…”