Rational Defect Passivation of Cu₂ZnSn(S,Se)₄ Photovoltaics with Solution-Processed Cu₂ZnSnS₄:Na Nanocrystals

Abstract

An effective defect passivation route has been demonstrated in the rapidly growing Cu2ZnSn(S,Se)4 (CZTSSe) solar cell device system by using Cu2ZnSnS4:Na (CZTS:Na) nanocrystals precursors. CZTS:Na nanocrystals are obtained by sequentially preparing CZTS nanocrystals and surface decorating of Na species, while retaining the kesterite CZTS phase. The exclusive surface presence of amorphous Na species is proved by X-ray photoluminescence spectrum and transmission electron microscopy. With Na-free glasses as the substrate, CZTS:Na nanocrystal-based solar cell device shows 50% enhancement of device performance (∼6%) than that of unpassivated CZTS nanocrystal-based device (∼4%). The enhanced electrical performance is closely related to the increased carrier concentration and elongated minority carrier lifetime, induced by defect passivation. Solution incorporation of extrinsic additives into the nanocrystals and the corresponding film enables a facile, quantitative, and versatile approach to tune the defect property of materials for future optoelectronic applications.

Significantly Enhancing Grain Growth in Cu2ZnSn(S,Se)4 Absorber Layers by Insetting Sb2S3, CuSbS2, and NaSb5S8 Thin Films

“…24 Moreover, Yang's group has synthesized CZTS:Na + nanocrystals for enhancing the CZTSSe device performance. 25 Additionally, Su et al 19 and our group 26 have reported that the crystallinity of CZTS thin films can be improved by incorporating Na + into CZTS precursor solution, and SutterFella's group has also observed a massive improvement in grain growth by depositing NaF and selenium and then forming liquid Na 2 Se x phases in the annealing process. 20 Furthermore, Aydil and co-workers particularly studied the distinguishing ability of Na, K, and Ca for enhancing CZTS grain growth, 27 and then they conducted a systematic study of controlling crystal growth and microstructure development by controlling the annealing temperature, annealing time, sulfur pressure, and substrate.…”

Rational synthesis of (Cu1−xAgx)2ZnSnS4 nanocrystals with low defect and tuning band gap

“…Until now, several chemical strategies had been developed to reduce defects or increase carrier concentration in CZTS materials. For example, sodium doping or treatment is found to increase carrier concentration and/or mobility and passivate deep defects in CZTS [11][12]. For most compound semiconductors, it is commonly accepted substitution of atom from same group in periodic table results in band-gap engineering.…”

Bifacial sodium-incorporated treatments: Tailoring deep traps and enhancing carrier transport properties in Cu2ZnSnS4 solar cells

“…Among these approaches, sodium incorporation has been demonstrated to be effective and beneficial in passivating defects in the CZTS absorbers, resulting in an improved device performance [23][24][25]. Various methodologies have been employed for effective incorporation of sodium, including out-diffused from the soda lime glass (SLG) substrate during thermal annealing processes and supplied as ex-situ dopants during or after the growth processes [22,24]. However, to achieve efficient and homogeneous passivation of grain boundary defects in the CZTS photo-absorber remains a challenge, particularly for those fabricated by solution-based processes, because of their inferior crystallinity and large defect density.…”