Comparing strategies for improving efficiencies in vacuum processed Cu2ZnSnSe4 solar cells

Abstract

In this study, we detail a Cu 2 ZnSnSe 4 based solar cell fabrication process based on the selenization of metallic precursor stacks with elemental Se. 9.4% efficient devices without antireflection coating have been obtained. First, reproducibility issues of the process are carefully shown and discussed. It is demonstrated that device performances are strongly impacted by the precise control of the precursor composition. Then, starting from this robust process, a review of existing strategies to improve kesterite efficiencies is conducted. A significant increase in efficiency (þ1.4% absolute efficiency and þ50 mV V OC) is obtained with absorber surface treatment and post-annealing, while no effect of Ge incorporation in the precursor stack is observed. This contradictory result to most of the recent publications raises the question of the universality of this strategy to improve kesterite solar cell performance. Finding a universal activation step to boost kesterite efficiencies and bring it to the market remains a crucial need for the community.

Homogeneous and Graded Ag Alloying in (Cu1‐xAgx)2ZnSnSe4 Solar Cells

“…The samples were positioned in a graphite susceptor with Se pellets and annealed at 520 C for 5 min at 8.5 Â 10 4 Pa Ar pressure in a lamp furnace. Additional details of the CZTSe absorber fabrication were shown in the study by Grenet et al [16] . Ag was deposited in an Alliance Concept DP1100 equipment with high-power impulse magnetron sputtering.…”

“…It is attributed to a decrease in the c/a ratio in the lattice when Ag replaces Cu. [7] Finally, for the ACA 50% sample, the signature of a surface SnSe 2 secondary phase is visible at 14.4 (only the low-angle peak is clearly visible [16] ) and is systematically present even when lowering the Sn content in the absorber. Thus, the synthesis of a CAZTSe pure phase with ACA %50% is not successfully achieved (at lower Ag content, no evidence of secondary phases has been obtained but the presence of a unique CZTSe phase cannot be claimed only based on XRD analysis).…”

“…In a first step, Cu/Sn/Cu/Zn/Se precursor stacks are annealed at 520 C in additional Se atmosphere to produce the desired material. The process is exhaustively described in the study by Grenet et al [16] No modification of the standard process is brought in this approach, particularly concerning the cationic composition: the thicknesses of the precursor stacks are not modified and are similar to those used in the highly efficient CZTSe technology. [16] The composition of the CZTSe absorbers is shown in Table 2.…”

“…The process is exhaustively described in the study by Grenet et al [16] No modification of the standard process is brought in this approach, particularly concerning the cationic composition: the thicknesses of the precursor stacks are not modified and are similar to those used in the highly efficient CZTSe technology. [16] The composition of the CZTSe absorbers is shown in Table 2. After CZTSe synthesis, a Ag thin layer (from 5 to 15 nm) is sputtered on top of the absorber without intentional heating.…”

Effect of Sb and Na Incorporation in Cu2ZnSnS4 Solar Cells

“…CZTS based solar cells are fabricated from metallic stacks of precursors identical to those used for the CZTSe technology . A Soda Lime Glass (SLG) substrate is first automatically cleaned and dried in a Pluritank USC120 MK4 from Novatec with successive ultrasonic and soap baths.…”