Device Simulation of 25.9% Efficient ZnOxNy${\rm ZnO}_x{\rm N}_y$/Si Tandem Solar Cell.

The novel, high electron mobility material ZnOxNy${\rm ZnO}_x{\rm N}_y$ has been investigated theoretically as an absorber in a two‐terminal tandem solar cell. In addition to its high mobility, ZnOxNy${\rm ZnO}_x{\rm N}_y$ can attain sufficiently low carrier concentration to enable pn$pn$‐junctions, and has a tunable bandgap around the 1.7 eV range. It is therefore suitable for pairing with a Si‐based bottom cell. In addition to the ZnOxNy${\rm ZnO}_x{\rm N}_y$ layer, the tandem cell consists of a Cu2O${\rm Cu}_2{\rm O}$ emitter and a Si heterojunction bottom cell. A buffer layer is introduced between the emitter and absorber in the top cell to mediate a large valence band offset that resulted in a poor fill factor, FF$FF$. A ZnOxNy${\rm ZnO}_x{\rm N}_y$ buffer layer bandgap of 1.5 eV gave the highest power conversion efficiency (PCE). The objective is to estimate the optimal performance of ZnOxNy${\rm ZnO}_x{\rm N}_y$ in a tandem solar cell. The dependence of current–voltage (J$J$–V$V$) characteristics on thickness, mobility and carrier concentration in the ZnOxNy${\rm ZnO}_x{\rm N}_y$ layer is evaluated, and found to yield maximum performance with 0.35 μm$\umu {\rm m}$, 250 cm2${\rm cm}^2$ Vs–1 and 1016$10^{16}$cm−3${\rm cm}^{-3}$, respectively. Using these conditions, the J$J$–V$V$ parameters of the device under AM1.5 illumination are short circuit current density, JSC=17.76$J_{SC}=17.76$ mA cm−2${\mathrm{cm}}^{-2}$, open circuit voltage, VOC=1.74$V_{OC}=1.74$ V, FF=83.8%$FF=83.8\%$ and PCE=25.9%${\rm PCE}\,=25.9\%$. With this, it is reported on, to the best of the knowledge, the first device simulation based on ZnOxNy${\rm ZnO}_x{\rm N}_y$. [ABSTRACT FROM AUTHOR]