Organic solar cells (OSCs) have gained significant interest due to their high-power conversion efficiency (PCE), mechanical flexibility, and potential for low-cost manufacturing. While certified PCEs over 19% have been achieved in bulk-heterojunction (BHJ) OSCs through advancements in donor and acceptor materials, progress in hole-transporting layers (HTLs) for conventional (p-i-n) structures remains limited. Critical factors such as morphology control, recombination dynamics in the photoactive layer, and the development of novel HTLs significantly influence both device performance and stability. To address these challenges, this thesis presents three innovative strategies aimed at enhancing both the efficiency and stability of OSCs through improved morphology optimization and surface engineering within the device architecture.

The first part of this work investigates the underlying causes of performance and stability losses in non-fullerene-based OSCs employing PEDOT:PSS and MoOx as hole transport layers. It highlights the beneficial effects of ultraviolet-ozone treatment in improving both efficiency and stability in MoOx-based devices. Based on these findings, a strategy is proposed to further enhance the performance and durability of non-fullerene OSCs by optimizing transition metal oxide-based HTLs in the p-i-n structure.

The second approach explores a formulation strategy by studying the performance and stability of optimized ternary blends that incorporate non-fullerene acceptors (NFAs), fullerenes, and functionalized fullerene molecules. A range of characterization techniques, including molecular dynamics simulations (conducted for the first time in this context), were employed. These analyses highlight the impact of using fullerenes as third components in NFA-based BHJ systems. The resulting ternary devices achieved outstanding PCEs exceeding 18%, along with improved photo-thermal stability attributed to fullerene incorporation.

Lastly, self-assembled monolayers (SAMs) are employed as HTLs in NFA-based OSCs, enabling PCEs surpassing 19%. However, these SAM-based devices exhibit limited operational stability under thermal and light stress. To overcome this limitation, we incorporated the previously optimized ultrathin evaporated MoOx layer, creating a hybrid anode structure consisting of ITO/MoOx-2PACz. Devices based on this hybrid anode demonstrated significantly enhanced operational stability, exceeding over 1000 hours under maximum power point tracking (MPPT) conditions, while maintaining comparable PCEs (~18%) to those using pristine 2PACz.