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

Abstract

The Cd‐free Cu2ZnSnS4 (CZTS) solar cell is an ideal candidate for producing low‐cost clean energy through green materials owing to its inherent environmental friendliness and earth abundance. Nevertheless, sulfide CZTS has long suffered from severe open‐circuit voltage (VOC) deficits, limiting the full exploitation of performance potential and further progress. Here, we propose an effective strategy to alleviate the non‐radiative VOC loss by manipulating the phase evolution during the critical kesterite phase formation stage. With a Ge cap layer on the precursor, premature CZTS grain formation is suppressed at low temperatures, leading to fewer nucleation centers at the initial crystallization stage. Consequently, the CZTS grain formation and crystallization are deferred to high temperatures, resulting in enhanced grain interior quality and less unfavorable grain boundaries in the final film. As a result, a champion efficiency of 10.7% for Cd‐free CZTS solar cells with remarkably high VOC beyond 800 mV (63.2% Schockley‐Queisser limit) is realized, indicating that non‐radiative recombination is effectively inhibited. This strategy may advance other compound semiconductors seeking high‐quality crystallization.This article is protected by copyright. All rights reserved

Facile Approach for Metallic Precursor Engineering for Efficient Kesterite Thin-Film Solar Cells

“…From the analysis, it has been observed that in CZTSSe, ACZTSSe TFSCs using “S- and E-Ag” was 0.310, 0.470, and 0.832 ns, respectively. Consequently, the enhancement of W d and the increase in τ contribute to efficient photogenerated carrier collection by reducing carrier recombination and ultimately resulting in an improved value of J sc …”

“…The large grains of kesterite at the top layer can effectively suppress the recombination rate at the buffer/absorber interface as well as minimize the formation of near-horizontal grain boundaries, leading to the improvement of device performance. 21,27,49 In this regard, the "alloying-Ag on Cu" TFSCs with the best device performance appears to be the optimum condition for Ag-induced precursor engineering for ACZTSSe TFSCs.…”

“…Consequently, the enhancement of W d and the increase in τ contribute to efficient photogenerated carrier collection by reducing carrier recombination and ultimately resulting in an improved value of J sc . 27 The dark I−V curve was performed to assess the quality of the bulk and absorber/buffer interfaces. 36 We have listed the dark I−V parameters such as diode ideal factor (n), series resistance (R s ), shunt conductance (G sh ), and reverse saturation current (J 0 ) as shown in Figures 6c,d and S10 and Table S3.…”

“…In the metal precursor-based synthesis process for high-performance CZTSSe TFSCs, achieving a single dense microstructure with minimal defects is significantly challenging. , One effective strategy that has been recently reported is the large grain growth (∼500 nm) using the Sn y (S x ,Se 1– x ) 2– y liquid phase-assisted approach . However, it often leads to issues like substantial Sn-loss or defective Sn-rich kesterite surface owing to uncontrollable Sn­(S,Se) x vapor pressure .…”

Tailoring Addition Sequence of Metal Ions in Precursor Solution Drives Highly Efficient Kesterite Solar Cells

“…[1] Then they proposed phase transition intervention by introducing a Ge cap layer on the precursor, delaying the formation and crystallization of Cu 2 ZnSnS 4 (CZTS) grains to high temperatures, thus improving the internal quality of the grains. [14] Kang's group in South Korea changed the crystal growth characteristics and reduced the defect energy level by designing different stacking sequences of precursors. [15] In addition, Xin's Group in NJUPT induced two different grain growth mechanisms and reaction pathways by changing the Sn oxidation state (Sn 2+ /Sn 4+ ) in the precursor solution, improving multi-layer structure of kesterite and increasing PCE.…”