Solution processable wurtzite CuInS2 inverted type solar cell

- Solution processable wurtzite and chalcopyrite solar cells are compared.
- Wurtzite solar cell shows 6.72% efficiency compared to 5.31% for chalcopyrite cell.
- Band gap of wurtzite phase is slightly higher than that of chalcopyrite phase.
- Larger grains and lower porosity are formed in case of wurtzite phase.
- Wurtzite phase shows near stoichiometry compared to Cu-rich character of chalcopyrite.

The solar cell efficiency of solution processable CuInS2 inverted type solar cells in two different crystal structures of chalcopyrite and wurtzite are compared. The solvothermal process in assistance with pre-dissolving the precursors is used to control the crystalline phases and the electrophoretic deposition is utilized to deposit absorber layer. The XRD and Raman spectroscopies confirm the formation of chalcopyrite and wurtzite phases without any trace of impurity phases. The band gap of wurtzite phase is slightly higher than that of chalcopyrite phase. However, the wurtzite film consists of larger grains and lower porosity, which are beneficial in solar cell application. Furthermore, the chalcopyrite phase crystallizes in Cu-rich phase compared with the wurtzite phase with slightly Cu-rich compound which play a crucial role in higher carrier concentration of the absorber in the presence of high sulfur content. The inverted type solution processed chalcopyrite cell shows 5.31% efficiency (JSC of 14.90 mA/cm2, VOC of 585 mV, and FF of 0.61), which is enhanced up to 26% compared with the wurtzite cell and reaches 6.72% (JSC of 17.80 mA/cm2, VOC of 590 mV, and FF of 0.64).

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