Recently, metal halide perovskite-based top cells have shown significant potential for use in inexpensive and high-performance tandem solar cells. In state-of-the-art p-i-n perovskite/Si tandem devices, atomic-layer-deposited SnO₂ has been widely used as a buffer layer in the top cells because it enables conformal, pinhole-free, and highly transparent buffer layer formation. In this work, the effects of various electrical properties of SnO₂ and C60 layers on the carrier transport characteristics and the performance of the final devices were investigated using a numerical simulation method, which was established based on real experimental data to increase the validity of the model. It was found that the band alignment at the SnO₂/C60 interface does, indeed, have a significant impact on the electron transport. In addition, as a general design rule, it was suggested that at first, the conduction band offset (CBO) between C60 and SnO₂ should be chosen so as not to be too negative. However, even in a case in which this CBO condition is not met, we would still have the means to improve the electron transport characteristics by increasing the doping density of at least one of the two layers of C60 and/or SnO₂, which would enhance the built-in potential across the perovskite layer and the electron extraction at the C60/SnO₂ interface.

Kesterite-structured Cu₂ZnSnSe₄ (CZTSe) is considered as one of the Earth-abundant and non-toxic photovoltaic materials. CZTSe films have been prepared using a single-step co-evaporation method at a relatively low temperature (i.e., below 500 °C). Due to the volatile nature of tin-selenide, the control over substrate temperature (i.e., growth temperature) is very important in terms of the deposition of high-quality CZTSe films. In this regard, the effects of growth temperatures on the CZTSe film morphology were investigated. The suitable temperature range to deposit CZTSe films with Cu-poor and Zn-rich compositions was 380–480 °C. As the temperature increased, the surface roughness of the CZTSe film decreased, which could improve p/n junction properties and associated device performances. Particularly, according to capacitance-voltage (C-V) and derived-level capacitance profiling (DLCP) measurements, the density of interfacial defects of CZTSe film grown at 480 °C showed the lowest value, of the order of ~3 × 10¹⁵ cm⁻³. Regardless of applied growth temperatures, the formation of a MoSe₂ layer was rarely observed, since the growth temperature was not high enough to have a reaction between Mo back contact layers and CZTSe absorber layers. As a result, the photovoltaic (PV) device with CZTSe film grown at 480 °C yielded the best power conversion efficiency of 6.47%. It is evident that the control over film growth temperature is a critical factor for obtaining high-quality CZTSe film prepared by one-step process.

The precursors of SnO₂ or In₂O₃/SnO₂ nanocrystlline powders have been prepared bythe sol-precipitation method. The precursors were calcined at different temperatures to prepareSnO₂ or In₂O₃/SnO₂ nanocrystalline powders with different particle sizes. The nanocrystalliteswere examined by differential thermal analysis (DTA), X-ray diffraction (XRD) andtransmission electron microscopy (TEM). And then thick film CO sensors were fabricated usingprepared SnO₂ or In₂O₃/SnO₂ nanocrystlline powders loaded with PdO_x. The composition thatgave the highest sensitivity for CO was in the weight% ratio of 5 wt.% In₂O₃/SnO₂:PdO_x as99:1(wt %). The composite material was found sensitive against CO at the working temperature200 °C. It was found that the sensors based on In₂O₃/SnO₂ nanocrystalline system exhibitedvery short response time to CO at ppm level. These characteristics make the sensor to be apromising candidate for detecting low concentrations of CO.