Surface Band Bending Engineered via Lithium‐Induced Reconstruction for Minimized Voltage Deficit in Kesterite Solar Cells

Why It Matters

By mitigating the dominant voltage deficit, the lithium‑induced surface engineering pushes kesterite solar cells closer to commercial viability and narrows the performance gap with established thin‑film technologies.

Key Takeaways

• Lithium spin-coating creates n-type ZnLi surface defects.
• Strong band bending improves p‑n conversion at CZTSSe/CdS interface.
• Voltage deficit reduced to 0.266 V, VOC ~570 mV.
• Champion efficiency reaches 14.92% (certified 14.52%).
• LiZn shallow defects suppress CuZn antisites, lowering recombination.

Pulse Analysis

Kesterite compounds such as Cu₂ZnSn(S,Se)₄ have attracted attention as earth‑abundant alternatives to cadmium‑based thin‑film photovoltaics, yet their commercial adoption has been hampered by a persistent open‑circuit voltage deficit. The deficit originates from deep‑level Cu/Zn antisite defects that create electrostatic potential fluctuations and misalign the conduction and valence bands at the CZTSSe/CdS interface. Consequently, non‑radiative recombination dominates, capping efficiencies well below the Shockley‑Queisser limit. Researchers have therefore focused on interface engineering strategies that can realign energy levels without compromising the absorber’s bulk quality.

The new lithium‑induced reconstruction tackles this problem by spin‑coating a concentrated Li‑containing solution onto the CZTSSe precursor, followed by a mild anneal. Lithium preferentially incorporates as ZnLi donor complexes, establishing a weak n‑type surface layer that produces pronounced upward band bending. This built‑in electric field drives efficient p‑n junction formation with the CdS buffer, while simultaneously generating LiZn shallow‑level states that passivate CuZn antisites. The combined effect suppresses interface traps, reduces non‑radiative pathways, and lifts the open‑circuit voltage to nearly 570 mV.

The reported champion cell delivers 14.92 % power conversion efficiency, with a certified 14.52 % and a voltage deficit of only 0.266 V, representing a record for lithium‑treated kesterite devices. Beyond the headline numbers, the technique is compatible with existing roll‑to‑roll manufacturing and uses inexpensive lithium salts, making scale‑up feasible. If adopted broadly, this surface‑band‑bending approach could narrow the performance gap between kesterite and mature technologies such as CIGS, accelerating the transition to low‑cost, toxic‑free photovoltaics in utility‑scale markets.