In this paper, a n-i-p planar heterojunction simulation of Sn-based iodide perovskite solar cell (PSC) is proposed. The solar cell structure consists of a Fluorine-doped tin oxide (FTO) substrate on which titanium oxide (TiO2) is placed; this material will act as an electron transporting layer (ETL); then, we have the tin perovskite CH3NH3SnI3 (MASnI3) which is the absorber layer and next a copper zinc and tin sulfide (CZTS) that will have the function of a hole transporting layer (HTL). This material is used due to its simple synthesis process and band tuning, in addition to presenting good electrical properties and stability; it is also a low-cost and non-toxic inorganic material. Finally, gold (Au) is placed as a back contact. The lead-free perovskite solar cell was simulated using a Solar Cell Capacitance Simulator (SCAPS-1D). The simulations were performed under AM 1.5G light illumination and focused on getting the best efficiency of the solar cell proposed. The thickness of MASnI3 and CZTS, band gap of CZTS, operating temperature in the range between 250 K and 350 K, acceptor concentration and defect density of absorber layer were the parameters optimized in the solar cell device. The simulation results indicate that absorber thicknesses of 500 nm and 300 nm for CZTS are appropriate for the solar cell. Further, when optimum values of the acceptor density (NA) and defect density (Nt), 1016 cm−3 and 1014 cm−3, respectively, were used, the best electrical values were obtained: Jsc of 31.66 mA/cm2, Voc of 0.96 V, FF of 67% and PCE of 20.28%. Due to the enhanced performance parameters, the structure of the device could be used in applications for a solar energy harvesting system.
Photodiode's reflectance plays an important role regarding the relation between responsivity and the incident flux. In this work we analyze how the spectral reflectance changes among photodiodes from the same manufacturer and batch and how the reflectance of three standard photodiodes has drifted during six years. The results show that the reflectance changes from diode to diode within the same batch and also show that the reflectance of photodiodes changes on time. This ageing is spectrally dependent.Silicon photodiodes are more sensitive and quicker than thermal detectors. For these reasons silicon photodiodes are used to maintain scales of spectral responsivity in the spectral range (300 nm -1000 nm) in many National Laboratories [1][2][3][4][5] .The spectral responsivity of a photodiode depends on the reflectance and the internal quantum efficiency, so a good approach to determine responsivity is to know both reflectance and internal quantum efficiency. Because of that, in this work we present a study about the reflectance of silicon photodiodes, with two goals: to study the variability of reflectance among photodiodes from a single batch, and to study the reflectance aging of some silicon photodiodes used as standards during six years. In some radiometric applications, the reflectance of individual photodiodes plays an important role because they have to match to a pair or be minimized or maximized, as it is the case for silicon trap radiometers [6,7] . The ageing of silicon photodiodes has been studied by several authors and all of them looked at the stability of the internal quantum efficiency [8,9] rather than at the reflectance.
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