Numerical Modeling and Analysis of HTM-Free Heterojunction Solar Cell Using SCAPS-1D

In this research paper, a HTM-free perovskite solar cell (PSC) structure with Titanium (TiO2), methyl ammonium lead triiodide (CH3NH3PbI3) and platinum (pt) as electron transport material (ETM), photon harvester and metal back contact is proposed. Solar Cell Capacitance Simulator (SCAPS-1D) program was used to implement the model and simulation. Effect of parameters such as thickness of ETM, thickness of absorber, doping concentration of ETM & absorber and electron affinity (EA) of ETM were investigated systematically. From the obtained results, it was found that the parameters affect the performance of the solar cell. When the thickness of ETM was varied from 0.02 to 0.10 μm. The results show that photovoltaic parameters decrease with the thickness increase. When the thickness of the absorber was varied from 0.1 to 1.0 μm, the optimized value was found at thickness of 0.4 . When the doping concentration of absorber and EMT were varied from 1010–1017 cm-3 and from 1015–1020 cm-3, the highest values of PCEs were obtained at 1016 cm-3 and 1020 cm-3 for Absorber and ETM. Also when the EA was varied in the range of 3.7 eV to 4.5 eV, the optimized value was at 3.7 eV. Upon optimization of the above mentioned parameters, power conversion efficiency (PCE) was found to be 25.75 %, short circuit current density (Jsc) 23.25 mAcm-2, open circuit voltage (Voc) 1.24 V and fill factor (FF) 89.50 %. The optimized result shows an improvement of ~1.95 times in PCE, ~1.06 times in Jsc, ~1.44 times in Voc and ~1.28 times in FF as compared to the initial device with the following parameters, PCE=13.22 %, Jsc=21.96 mAcm−2, Voc=0.86 V and FF=69.94 %.

Properties of Arsenic–Doped ZnTe Thin Films as a Back Contact for CdTe Solar Cells

As-doped polycrystalline ZnTe layers grown by metalorganic chemical vapor deposition (MOCVD) have been investigated as a back contact for CdTe solar cells. While undoped ZnTe films were essentially insulating, the doped layers showed significant rise in conductivity with increasing As concentration. High p-type carrier densities up 4.5 × 1018 cm−3 was measured by the Hall-effect in heavily doped ZnTe:As films, displaying electrical properties comparable to epitaxial ZnTe single crystalline thin films in the literature. Device incorporation with as-deposited ZnTe:As yielded lower photovoltaic (PV) performance compared to reference devices, due to losses in the open-circuit potential (VOC) and fill factor (FF) related to reducing p-type doping density (NA) in the absorber layer. Some minor recovery observed in absorber doping following a Cl-free post–ZnTe:As deposition anneal in hydrogen at 420 °C contributed to a slight improvement in VOC and NA, highlighting the significance of back contact activation. A mild CdCl2 activation process on the ZnTe:As back contact layer via a sacrificial CdS cap layer has been assessed to suppress Zn losses, which occur in the case of standard CdCl2 anneal treatments (CHT) via formation of volatile ZnCl2. The CdS sacrificial cap was effective in minimising the Zn loss. Compared to untreated and non-capped, mild CHT processed ZnTe:As back contacted devices, mild CHT with a CdS barrier showed the highest recovery in absorber doping and an ~10 mV gain in VOC, with the best cell efficiency approaching the baseline devices.