Giant Voc Boost of Low‐Temperature Annealed Cu(In, Ga)Se2 with Sputtered Zn(O, S) Buffers. Issue 9 (30th May 2019)

• Record Type: Journal Article
• Authors: Zutter, Marco; Virtuoso, Jose; Anacleto, Pedro; Yasin, Liam; Alves, Marina; Madeira, Miguel; Bondarchuk, Oleksandr; Mitra, Saibal; Fuster Signes, David; Garcia, Jorge M.; Briones, Fernando; Waechter, Rolf; Kiowski, Oliver; Hariskos, Dimitrios; Colombara, Diego; Sadewasser, Sascha
• Is Part Of: Physica status solidi. Volume 13:Issue 9(2019)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2019-05-30
• Subjects: buffer layer -- CIGS solar cells -- Cu(In, Ga)Se2 -- interface recombination -- sputter deposition -- Zn(O, S); Solid state physics -- Periodicals; 530.4105
• DOI: 10.1002/pssr.201900145
• Languages: English
• ISSNs: 1862-6254

Abstract

Abstract : Large‐scale industrial fabrication of Cu(In, Ga)Se2 (CIGS) photovoltaic panels would benefit significantly if the buffer layer chemical bath deposition could be replaced by a cadmium‐free dry vacuum process suitable for in‐line production. This Letter reports on the development of a Zn(O, S) buffer layer deposited by vacuum‐based magnetron sputtering from a single target onto commercial CIGS absorbers cut from a module‐size glass/Mo/CIGS stack. The buffer‐window stack consisting of Zn(O0.75 S0.25 )/i‐ZnO/ZnO:Al is optimized for layer thickness and optical and electronic properties, leading to an average device efficiency of 4.7%, which can be improved by annealing at 200 °C to a maximum of 10.5%, mainly due to a considerable increase in the open‐circuit voltage ( V oc ). Temperature‐dependent current density versus voltage ( J – V ) characteristics show a reduced interface recombination upon annealing, explaining the observed V oc boost. Quantum efficiency shows improvements in the long and short wavelength region, setting in at different annealing temperatures, and photoemission depth profiling indicates interdiffusion of all atomic species at the CIGS/Zn(O, S) interface. Electrical device simulations explain the observed effects by a modification of the band offset at the interface and defects passivation. Both effects are attributed to the observed interdiffusion during annealing. Abstract : Cu(In, Ga)Se2 solar cells comprising sputtered Zn(O, S) buffers incur substantial open‐circuit voltage improvements upon 200 °C annealing. Temperature‐dependent electrical analysis reveals that recombination shifts from interface to bulk. Concurrently, ultraviolet‐photoelectron spectroscopy reveals a 0.3 eV increase in the work function of Zn(O, S). Solar‐cell‐capacitance simulations are consistent with the change of conduction band offset and with the observed wavelength‐dependent improvement of charge‐carrier collection.