Over 11 % efficient eco-friendly kesterite solar cell: Effects of S-enriched surface of Cu2ZnSn(S,Se)4 absorber and band gap controlled (Zn,Sn)O buffer

Interface engineering of p-n heterojunction for kesterite photovoltaics: A progress review

“…ZnO 1-x S x (Zn(O,S)) and Zn 1-x Sn x O y (ZnSnO) are suitable Cd-free alternative buffer layers when considering environmental impact, materials scarcity and bandgap tunability. Recently, replacing the CdS layer with Zn(O,S) or ZnSnO has been intensively studied in kesterite solar cells [44,45,47,49,[68][69][70][71][72]. Though Zn(O,S) shows a large tunable bandgap, kesterite solar cells with this buffer layer still possess low efficiencies (<8%) [68,71].…”

“…Since 2017, the record efficiency of the Cd-free kesterite device has been achieved back to back by replacing CdS with a ZnSnO buffer layer, making a major breakthrough in the search for an alternative buffer layer [41,44,45,47,49]. Atomic layer deposition (ALD) is a widely accepted method to deposit the ZnSnO buffer.…”

“…Further enhancement in performance has been enabled by optimization of the absorber to accurately match the band alignment, resulting in 9.7% efficiency [45]. To date, the efficiencies of Cd-free kesterite solar cells lie beyond 10% and 11% for CZTS and CZTSSe, respectively [41,44]. Reduced interface recombination resulting from better band alignment and/or formation of a Zn(O,S) passivating layer could be the main contribution of the ZnSnO buffer layer [45].…”

“…Fig. 1 shows the recent PCE evolution of kesterite PV enabled by different heterojunction engineering, including an alternative buffer layer, heterojunction treatment (HT) and passivation layer [1,[40][41][42][43][44][45][46][47][48][49][50]. Impressively, a major breakthrough in CZTS was achieved by heterojunction treatment, resulting in a record PCE of 11% [1].…”

“…Similarly, HT for CZTSSe reveals significant enhancement in V oc and FF, indicating effectiveness of HT in altering the heterojunction quality of kesterite solar cell [50]. Furthermore, beyond 10% CZTS and CZTSSe have been developed with a Cd-free buffer layer, making this low-cost and green absorber attractive to potential commercial interests [41,44]. The significant research progress on the p-n heterojunction interface thus needs to be reviewed to inspire researchers to pursue more efficient kesterite PV.…”