Enhancing solar cell efficiency through tandem structures utilizing lead-free mixed cation perovskites and CZTSe absorber layers

A tandem structure efficiently boosts solar cell efficiency because it uses a larger spectrum of solar radiation and minimizes photon energy thermalization. High-performance tandem solar cells have historically been difficult to produce due to a shortage of high-performance, low-bandgap cells. The proposed design is based on the CH3NH3GeI3 (1.9 eV) as a wide band gap absorber layer and FAMASnGeI3 (1.4 eV) as a narrow band gap perovskite layer with CZTSe as HTL. This research investigates the effect of different ETLs, perovskite layer thicknesses and their doping concentration on the device's photovoltaic parameters. Furthermore, the effect of tunnel junction thickness and front contact work function on the solar cell performance has also been simulated. It has been noted that the PCBM presents a better efficiency device than the other ETLs. The Voc of different ETLs has been related to Vbi. Moreover, the optimized thicknesses of both perovskite absorber layers are 450 nm and 400 nm for MAGeI3 and FAMASnGeI3, respectively. The optimal doping density is found to be E14 cm−3. It has been observed that the tunnel junction's thickness and the front contact's work function also play an important role in optimized device efficiency. The tunnel junction thickness is 4 nm for lead-free mixed cation perovskite/CZTSe tandem solar cells. However, the work function of the front electrode of 4.4 eV is optimum for this structure. The proposed lead-free mixed cation perovskite/CZTSe tandem device shows significant performance parameters, i.e., Voc= 0.970 V, Jsc = 28.46 mAcm−2, FF = 84.43 % and PCE= 23.32 %