Stability of Sn-Pb mixed organic–inorganic halide perovskite solar cells:Progress,challenges,and perspectives

The exploration of low bandgap perovskite material to approach Shockley-Queisser limit of photovoltaic device is of great significance,but it is still challenging.During the past few years,tin–lead(Sn-Pb)mixed perovskites with low bandgaps have been rapidly developed,and their single junction solar cells have reached power conversion efficiency(PCE)over 21%,which also makes them ideal candidate as low bandgap sub-cell for tandem device.Nevertheless,due to the incorporation of unstable Sn^(2+),the stability issue becomes the vital problem for the further development of Sn-Pb mixed perovskite solar cells(PSCs).In this review,we are dedicated to give a full view in current understanding on the stability issue of SnPb mixed perovskites and their PSCs.We begin with the demonstration on the origin of instability of Sn-Pb mixed perovskites,including oxidation of Sn^(2+),defects,and interfacial layer induced instability.Sequentially,the up-to-date developments on the stability improvement of Sn-Pb mixed perovskites and their PSCs is systematically reviewed,including composition engineering,additive engineering,and interfacial engineering.At last,the current challenges and future perspectives on the stability study of Sn-Pb mixed PSCs are discussed,which we hope could promote the further application of Sn-Pb mixed perovskites towards commercialization.

Electron back-scattering diffraction preliminary analysis of heterogeneous nuclei in magnesium alloy during solidification process under GPa high pressure

The effective heterogeneous nuclei in Mg-7.92 Zn-1.70 Y alloy during solidification process under high pressure was investigated by EBSD. It is found that the orientation relationship between Mg matrix and MgY phase, [111]_（MgY）//[1210]_（α-Mg） and（101）_（MgY）//（0001）_（α-Mg）, exists between Mg matrix and MgY phase.The MgY phase is the potential heterogeneous nuclei substrate for a-Mg solidified under high pressure. It is calculated by Bramfitt mode that the mismatch between Mg matrix and MgY phase is greater than 12% under atmospheric pressure. When solidified under high pressure of 4 GPa, the solidification pressure can increase the number of the α-Mg nucleus by reducing the size of the nucleus, decreasing interfacial energy of MgY/a-Mg, and changing the wettability between MgY phase and α-Mg from non-wetting under atmospheric pressure to wetting under high pressure. The MgY phase becomes a powerful heterogeneous nuclei for α-Mg crystal. Increasing the number of valid heterogeneous nuclei substrate increases nucleus number and refines the grain of the alloy.