Evaluation of different metal salt solutions for the preparation of solar cells with wide-gap Cu₂ZnGeS_xSe_4−x absorbers

Abstract

In this work, thin-film solar cells with a kesterite-type Cu2ZnGeSxSe4−x (CZGSSe) absorber were prepared from four different metal salt solutions.

Band Gap Tuning of Cu2ZnGeSxSe4-x Absorbers for Thin-Film Solar Cells

“…Its similarity to the extensively studied Cu 2 ZnSnS x Se 4-x (CZTSSe) offers potential for fast progress in the improvement of material properties and solar cell efficiency, with a record value of 6.0% so far [3]. However, the band gaps in previous publications are in a range between 1.4 eV [4] and 1.5 eV [5] and are therefore still too low for application as top cells in multijunction solar cells.…”

“…Further details about the metal salt solution can be found in Ref. [5]. In a second step, the precursor layer was annealed for 15 min at 550 • C in an Se-containing nitrogen atmosphere to induce grain growth and to exchange S for Se to form the CZGSSe absorber.…”

Doping and alloying of kesterites

“…Thus, the full range of Ge substitution has been investigated to some extent, including the pure Ge compound in recent reports, demonstrating that the CZGSe exhibits also kesterite structure [123]. Among the most relevant pure Ge kesterite results, Schnabel et al reported efficiencies exceeding 5% for a sulfo-selenide CZGSSe (E g ∼1.5 eV) solar cell [124], while for the selenide CZGSe (Eg∼1.4 eV) compound, Sahayaraj et al published a 5.5% efficiency device with a remarkable V OC of 744 mV [125]. Intriguingly, the Ge based kesterite showed less electrical losses from band tailing/electrostatic potential fluctuations compared to Ge free devices [125,126].…”

Uncovering details behind the formation mechanisms of Cu2ZnGeSe4 photovoltaic absorbers

“…20 Similar absorber compound witnessed an open circuit voltage of 744 mV recognized as the highest V OC obtained with a device efficiency of 5.5%. 21,22 The investigation on Ge-substituted kesterite could be additionally interesting in order to broaden the application of kesterites, allowing to go towards wider bandgap materials for PV tandem solar cells or semi-transparent devices. Nevertheless, this material has been much less studied than its Sn-based counterpart, and although recently first important studies about the fundamental properties of CZGeSe have been published, [23][24][25][26][27][28][29][30][31] there are still several issues that need to be addressed for further progress.…”