Numerical Investigation of Absorber-Layer Thickness, Defect Density and Temperature Effects in a Non-Fullerene Organic Solar

Abstract

This study numerically examines three parameters that strongly influence the performance of a non-fullerene organic solar cell: the thickness of the PBDB-T:ITIC photoactive layer, the bulk defect density within the absorber, and the operating temperature. A fixed FTO/PDINO/PBDB-T:ITIC/CFTS/Al architecture is considered so that the observed changes can be attributed to the parameter under investigation rather than to changes in device structure. The device is modeled with the one-dimensional Solar Cell Capacitance Simulator (SCAPS-1D) under AM1.5G illumination at 100 mW cm⁻². The results show that increasing the active-layer thickness from 80 to 200 nm raises the calculated efficiency from 9.65% to 16.86%, after which further thickening reduces efficiency. At a fixed 200 nm absorber thickness, increasing defect density from 10¹³ to 10¹⁸ cm⁻³ progressively reduces efficiency from 19.49% to 4.06%. An increase in temperature from 250 to 400 K similarly decreases efficiency from 18.54% to 10.88%. The results demonstrate that an optimum thickness exists because optical absorption and carrier extraction compete with transport and recombination losses, while high defect density and elevated temperature primarily penalize voltage and fill factor. The numerical trends provide a compact parameter map for subsequent optimization of the same device architecture.