Newford Research Institute of Advanced Technology

Abstract Silicon‐based tandem solar cells are regarded as one of the most feasible ways to break the single‐junction Shockley–Queisser limit efficiency and further reduce the cost of solar electricity. Recently, wide‐bandgap (≈1.7 eV) perovskite solar cells have drawn intense research interest as the top cell for Si‐based tandem devices. Despite significant progress in device efficiency, the unsatisfactory stability of perovskites is still a huge concern. Besides halide perovskites, there are many inorganic semiconductors worthy of investigation. It is believed that cadmium selenide, a binary compound enjoying outstanding optoelectronic properties, high stability, and low cost, is very promising as the top cell for Si‐based tandem devices. Herein, the CdSe thin‐film solar cells that have been neglected for 3 decades are revisited. Using rapid thermal evaporation, high‐quality CdSe thin films with large grain size, high‐photoluminescence, small Stokes shift, and intrinsic n‐type conductivity are obtained. Furthermore, CdSe solar cells are redesigned and a champion efficiency of 6.00% is achieved. Through in‐depth analysis, it is identified that bulk and interface defects limit the open‐circuit voltage and hence device performance. This work highlights the great potential of CdSe solar cells as top cells for Si‐based tandem devices.

Abstract In the present study, (1 − x)BaAl2Si2O8−xCaSnSiO5−y wt.% LiF microwave dielectric ceramics were prepared through the traditional solid‐state sintering at 950−1395°C for 5 h. The BaAl2Si2O8 phase could coexist with the CaSnSiO5 phase at (1 − x)BaAl2Si2O8−xCaSnSiO5 (.2 ≤ x ≤ .6) ceramics, and no other secondary phase was observed. The CaSnSiO5, as a τf regulator, adjusted the negative τf value of BaAl2Si2O8 to near zero. Excellent microwave dielectric properties (εr = 8.1, Q × f = 37 560 GHz, and τf = −1.5 ppm/°C) were obtained from the 0.6BaAl2Si2O8−0.4CaSnSiO5 ceramic. The sintering temperature of 0.6BaAl2Si2O8−0.4CaSnSiO5 ceramic decreased from 1375°C to 950°C by introducing 2 wt.% LiF. The 0.6BaAl2Si2O8−0.4CaSnSiO5−2 wt% LiF ceramic exhibited remarkable microwave dielectric properties (εr = 7.6, Q × f = 17 420 GHz, and τf = −12.2 ppm/°C) and could be applied to the low‐temperature co‐fired ceramic (LTCC) field.