Abstract:In a monolithic perovskite/c-Si tandem device, the perovskite top cell has to be deposited onto a flat c-Si bottom cell without anti-reflective front side texture, to avoid fabrication issues. We use optical simulations to analyze the reflection losses that this induces. We then systematically minimize these losses by introducing surface textures in combination with a so-called burial layer to keep the perovskite top cell flat. Optical simulations show that, even with a flat top cell, the monolithic perovskite/c-Si tandem device can reach a matched photocurrent density as high as 19.57 mA/cm Korte, R. Schlatmann, M. K. Nazeeruddin, A. Hagfeldt, M. Gratzel, and B. Rech, "Monolithic perovskite/silicon-heterojunction tandem solar cells processed at low temperature," Energy Environ. Sci. 9(1), 81-88 (2015). 16.

No abstract

No abstract

No abstract

We have applied an optical splitting system in order to achieve very high conversion efficiency for a full spectrum multi-junction solar cell. This system consists of multiple solar cells with different band gap optically coupled via an “optical splitter.” An optical splitter is a multi-layered beam splitter with very high reflection in the shorter-wave-length range and very high transmission in the longer-wave-length range. By splitting the incident solar spectrum and distributing it to each solar cell, the solar energy can be managed more efficiently. We have fabricated optical splitters and used them with a wide-gap amorphous silicon (a-Si) solar cell or a CH3NH3PbI3 perovskite solar cell as top cells, combined with mono-crystalline silicon heterojunction (HJ) solar cells as bottom cells. We have achieved with a 550 nm cutoff splitter an active area conversion efficiency of over 25% using a-Si and HJ solar cells and 28% using perovskite and HJ solar cells.

We report the intrinsic critical current density (J c0 ) in current-induced magnetization switching and the thermal stability factor (E=k B T, where E, k B , and T are the energy potential, the Boltzmann constant, and temperature, respectively) in MgO based magnetic tunnel junctions with a Co 40 Fe 40 B 20 (2 nm)/Ru(0.7 -2.4 nm)/Co 40 Fe 40 B 20 (2 nm) synthetic ferrimagnetic (SyF) free layer. We show that J c0 and E=k B T can be determined by analyzing the average critical current density as a function of coercivity using the Slonczewski's model taking into account thermal fluctuation. We find that high antiferromagnetic coupling between the two CoFeB layers in a SyF free layer results in reduced J c0 without reducing high E=k B T.

ReceivedWe investigated dependence of tunnel magnetoresistance effect in CoFeB/MgO/CoFeB magnetic tunnel junctions on Ar pressure during MgO-barrier sputtering. Sputter deposition of MgO-barrier at high Ar pressure of 10 mTorr resulted in smooth surface and highly (001) oriented MgO. Using this MgO as a tunnel barrier, tunnel magnetoresistance (TMR) ratio as high as 355% at room temperature (578% at 5K) was realized after annealing at 325 o C or higher, which appears to be related to a highly (001) oriented CoFeB texture promoted by the smooth and highly oriented MgO. Electron-beam lithography defined deep-submicron MTJs having a low-resistivity Auunderlayer with the high-pressure deposited MgO showed high TMR ratio at low resistance-area product (RA) below 10 Ωμm 2 as 27% at RA = 0.8 Ωμm 2 , 77% at RA = 1.1 Ωμm 2 , 130% at RA = 1.7 Ωμm 2 , and 165% at RA = 2.9 Ωμm 2 .

We present a new version of our optical model for solar cell simulation: GENPRO4. Its working principles are briefly explained. The model is suitable for quickly and accurately simulating a wide range of wafer based and thin-film solar cells. Especially adjusting layer thicknesses to match the currents in multi-junction devices can be done with a minimum of computational cost. To illustrate this, a triple junction thin-film silicon solar cell is simulated. The simulation results show very good agreement with EQE measurements. The application of an MgF 2 anti-reflective coating or an anti-reflective foil with pyramid texture is considered. Their effects on the implied photocurrents of top, middle and bottom cell are investigated in detail.