Low-Cost CZTSSe Solar Cells Fabricated with Low Band Gap CZTSe Nanocrystals, Environmentally Friendly Binder, and Nonvacuum Processes

High quality Cu2ZnSn(SSe)(4) (CZTSSe) for solar cells can be fabricated with Cu2ZnSnS4 (CZTS) nanocrystals, followed by a selenization process. However, the use of toxic and environmentally unfriendly solvents such as toluene or hexanethiol to disperse the nanocrystals and the use of the harsh selenization process to promote the grain growth are not environmentally benign. We present here an environmentally friendly, sustainable, and scalable route to fabricate CZTSSe with Cu2ZnSnSe4 (CTZSe) nanocrystals by a sulfurization process. The CZTSSe film has been doped with S to optimize the device performance, exhibiting an enhancement in the open-circuit voltage (V-oc) and short circuit current density (J(sc)). In addition, by developing a robust precursor film with the addition of ethyl cellulose, the loss of Sn associated with the conversion of CZTSe to CZTSSe during the grain growth process has been mitigated, leading to an increase in the conversion efficiency compared to that of the precursor film without using ethyl cellulose. Such an improvement can provide insight into the grain growth of CZTSSe during the sulfurization process and thereby enhance the feasibility of sustainable high efficiency CZTSSe solar devices. KEYWORDS: Solar cells, Superstrate-type substrate, CZTSSe, Sulfurization, Sn loss, Ethyl.cellulose