A Facile Process for Partial Ag Substitution in Kesterite Cu₂ZnSn(S,Se)₄ Solar Cells Enabling a Device Efficiency of over 12%

Abstract

A cation substitution in Cu2ZnSn­(S,Se)4 (CZTSSe) offers a viable strategy to reduce the open-circuit voltage (V oc)-deficit by altering the characteristics of band-tail states, antisite defects, and related defect clusters. Herein, we report a facile single process, i.e., simply introducing a thin Ag layer on a metallic precursor, to effectively improve the device characteristics and performances in kesterite (Ag x ,Cu1–x )2ZnSn­(S y ,Se1–y )4 (ACZTSSe) solar cells. Probing into the relationship between the external quantum efficiency derivative (dEQE/dλ) and device performances revealed the V oc-deficit characteristics in the ACZTSSe solar cells as a function of Cu and Ag contents. The fabricated champion ACZTSSe solar cell device showed an efficiency of 12.07% and a record low V oc-deficit of 561 mV. Thorough investigations into the mechanism underpinning the improved performance in the ACZTSSe device further revealed the improved band-tailing characteristic, effective minority carrier lifetime, and diode factors as well as reduced antisite defects and related defect clusters as compared to the CZTSSe device. This study demonstrates the feasibility of effectively suppressing antisite defects, related defect clusters, and band-tailing characteristics by simply introducing a thin Ag layer on a metallic precursor in the kesterite solar cells, which in turn effectively reduces the V oc-deficit.

Band-gap-graded Cu2ZnSn(S,Se)4 drives highly efficient solar cells

“…8,9 However, the similar ion diffusion rates in the hightemperature sulfuration/selenization process and the complexity of defect physics associated with CZTSSe appear to be among the main challenges limiting the further improvement of kesterite device performance, demanding new and efficient step-change improvement strategies. 10,11 Numerous works have reported the passivation of the grain interior and grain boundary defects of CZTSSe, such as (i) the use of isoelectronic cation substitution (Ag, Li for Cu, Cd for Zn, and Ge for Sn) to reduce Cu Zn antisite defects or Sn-related deep energy level defects, [12][13][14][15][16][17][18] (ii) the artificial introduction of passivation layers at the front or back interface, [19][20][21] and (iii) alkali metal doping strategies to passivate grain boundary defects. [22][23][24] However, in the CZTSSe absorber layers, the flat bandgap structure cannot effectively improve the collection of photogenerated electrons and reduce the recombination even when efficient passivation methods are employed, requiring the development of further strategies, such as a graded bandgap.…”

Understanding defects and band tailing characteristics and their impact on the device performance of Cu2ZnSn(S,Se)4 solar cells

“…There have been three effective approaches proposed to solve band tailing issues in the kesterite system such as (i) revealing the origin of band tailing characteristics, 7 (ii) engineering anti-site defects by adjusting experimental parameters, 8 and (iii) suppressing cation disordering by distant isoelectronic cation substitutions 10 ( i.e. Cu site by Ag, 25 Zn site by Cd 26 and Sn site by Ge 27 ) or by doping alkali elements (Na, 28 K, 29 and Li 30 ). Given the fact that the defects, defect clusters, and band tailing characteristics from cation disordering have been theoretically and experimentally established in kesterite-based thin films, there have been a few investigations into correlations between defects, defect clusters, band tailing characteristics and device performances.…”

Improvement of Photovoltaic Performance of Cu2ZnSn(S,Se)4 Solar Cells by Modification of Back Electrode Interface with Amorphous Boron Nitride

“…Recently, kesterite‐based Cu 2 ZnSn(S,Se) 4 (CZTSSe) thin film solar cell is considered to be one of the most promising inorganic thin film photovoltaic devices owing to its similar crystal structure to the commercialized Cu(In,Ga)Se 2 (CIGS) solar cell, earth‐abundant and nontoxic compositions, as well as high absorption coefficient (α>10 4 cm –1 ) and adjustable direct band gap ( E g = 1.0–1.5 eV). [ 1–4 ] Currently, the highest certified power conversion efficiency (PCE) of 13% was obtained for CZTSSe‐based thin film solar cell by Xin et al., [ 5 ] demonstrating its substantial commercial prospect. While it is still much lower than PCE of the counterpart CIGS devices (23.5%) [ 6 ] and its Shockley‐Queisser limit (32.8%).…”

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band gap (E g = 1.0-1.5 eV). [1][2][3][4] Currently, the highest certified power conversion efficiency (PCE) of 13% was obtained for CZTSSe-based thin film solar cell by Xin et al, [5] demonstrating its substantial commercial prospect. While it is still much lower than PCE of the counterpart CIGS devices (23.5%) [6] and its Shockley-Queisser limit (32.8%).

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