In recent years, non-fullerene acceptors (NFAs) have attracted enormous interest in the field of organic solar cells (OSCs), they improve power conversion efficiency (PCE) compared to the classical fullerene acceptor. In this work, OSCs based on PBDB-T as the donor material and the very well-known NFA ITIC, along with its fluorinated and chlorinated derivatives (IT-2F, IT-4F, IT-2Cl, IT-4Cl) were fabricated to investigate the effect of the halogenation end group on the photovoltaic parameters. Optical characterization reveals that both chlorination and fluorination are effective in downshifting the molecular energy levels and redshifting the absorption spectra, which results in higher Jsc but lower Voc compared to pristine ITIC. In addition, the halogenated ITIC device exhibited enhanced FF and PCE. Various optoelectronic techniques were also used to investigate the charge recombination dynamics and charge extraction process. It has been found that (IT-2F, IT-2Cl) show suppressed monomolecular recombination compared to di-substituted NFA (IT-4F, IT-4Cl). Furthermore, fluorinated ITIC has a longer charge carrier recombination lifetime but a lower carrier extraction rate. Lastly, the best-performing device from the preceding component mixtures PBDB-T:IT-2F was exposed to thermal annealing at different stages of the fabrication process to investigate how annealing affects the photovoltaic parameters. According to our findings, both post and 2-stage annealing improve FF and PCE, but the latter is even more beneficial. In further studies, the annealing effect on the HTL layer (MoOx) has also been investigated. Annealing improved the MoOx’s work function, resulting in higher internal electric field that thereby facilitated hole extraction, as demonstrated by TPC where 2-stage annealed devices exhibited a faster carrier extraction rate.

Thesis explores the question of whether one-diode model can be extracted using soft-computing approaches based on indoor conditions. In thesis, three algorithms were selected using MATLAB for implementation, analysis and comparison. Thesis has proved that under indoor conditions, all three algorithms can accurately extract photovoltaic parameters under most illumination levels, but the extracted photovoltaic parameters cannot satisfy the physical meaning of photovoltaic parameters.