Solution processed organic semiconducting polymers are susceptible to solvent etching once deposited and many are mechanically fragile. To increase the scope of devices that may be fabricated by solution processing by enabling multilayer deposition from the solution state, a strategy is required to cross-link polymers following deposition. This has the benefit of increasing the fracture resistance of the layers. In addition, developing an additive capable of cross-linking already-developed polymers enables the use of existing polymers without redesigning them. In this project, I designed and synthesized a tetrahedral cross-linking agent capable of transforming solution processed polymers into solvent resistant and mechanically robust films, enabling the fabrication of perovskite solar cells with increased efficiency and compound solar cells exhibiting a 3000% increase in fracture toughness.