E Danladi, LF Koao, TE Motaung, A Usman, SV Motloung
Abstract The Cs 2 AgBiBr 6 double halide perovskite has catered for the problem related to lead toxicity and stability in perovskite solar cells (PSCs). Unfortunately, fundamental structural, optical, and electronic properties of Cs 2 AgBiBr 6 are still not yet fully understood, couple with the unstable hole transport layer (HTL) such as spiro-OMeTAD, limited diffusion length of charge carriers, interface defects, and inferior hole extraction capability results to poor performance. Here, we delve into thorough assessment of Cs 2 AgBiBr 6 as a feasible absorber material by deploying density functional theory (DFT) as a calculation tool. A band gap of 1.639 eV was obtained with contribution on Ag-4d and Br-4p orbitals. From the optical results, there was an observation of low optical losses, maximal absorptivity, larger reflectivity at the ultraviolet-visible regions, superior conductivity and suitable refractive index for application in opto-electronic devices. Guided by DFT investigation, we proposed a novel design of Cs 2 AgBiBr 6 graphene-based PSC with graphene intercalated between the HTL and the absorber. Numerical optimization of HTLs such as spiro-OMeTAD, CuO, Cu 2 O, CuSbS 2 , CBTS and Mg-CuCrO 2 using solar capacitance simulation tool (SCAPS-1D), shows Mg-CuCrO 2 as the optimal HTL. The graphene modified device demonstrates an improved performance. Moreover, there was a better band matching in the graphene modified PSC. In comparison to the graphene-free PSC that shows PCE of 6.70%, FF of 37.50%, J sc of 21.56 mA cm −2 and V oc of 0.83 V, the optimized graphene-based PSC shows the following metric performance PCE = 30.83%, FF = 90.87% J sc = 21.72 mA cm −2 and V oc of 1.58 V. The improved performance is attributed to the minimal recombination losses and improved suppression of non-radiative interfacial recombination. The outcomes of the present study have paved the way for the development of a less expensive and high performing PSC with graphene layer by managing and controlling defect states and non-radiative recombination.