High-performance parallel tandem MoTe₂/perovskite solar cell based on reduced graphene oxide as hole transport layer

Recently, the impressive achievements accomplished in multijunction (tandem) perovskite solar cells have triggered a huge research effort to boost their performance. Here, using a three-dimensional (3D) finite element method (FEM) technique, we propose and investigate a parallel tandem PSCs consisting of two absorbing layers of MoTe₂ and CH₃NH₃PbI₃ with cascaded bandgaps to more efficiently use the near-infrared (NIR) solar spectrum. Endowed with a bandgap of about 1 eV, the MoTe₂ layer in conjunction with a CH₃NH₃PbI₃ layer is able to broaden the light absorption range of structure beyond the wavelength of 800 nm, up to 1200 nm. In addition to this, the MoTe₂ material can not only appreciably harvest light even with a thickness as low as 20 nm due to their high absorption coefficient, but also make a perfect band alignment with the CH₃NH₃PbI₃ layer. As a result, the proposed multijunction PCS yields a high power conversion efficiency (PCE) of 18.52% with a V_OC of 0.83 V, J_sc of 26.25 mA/cm², and FF of 0.84, which is considerably greater than its corresponding single-junction PSCs with PCE, V_OC, J_sc, and FF of, 14.01%, 1.14 V, 15.20 mA/cm², and 0.81, respectively. Furthermore, to mitigate the V_OC loss caused by the low bandgap of MoTe₂, we demonstrate an increase in V_OC from 0.84 to 0.928 V and in PCE from 18.52% to 20.32%, when we replace a reduced graphene oxide (rGO) layer with Spiro-OMeTAD layer as a hole transport layer (HTL).