Stress in solar cells plays a crucial role in the reliability of photovoltaic (PV) modules. The influences on stress are as diverse as the number of different materials in a PV module and become more and more complex with the growing variety of PV modules for different applications. Within this dissertation, a set of 15 thermomechanical design rules is derrived to support and accelerate future PV module developments. Three methods are developed and applied: 1. Thermomechanical finite element method simulations of PV module designs (FEM). 2. µRaman spectroscopy of laminated solar cells (µRaman). 3. Solar cell integrated stress sensors (SenSoCell). Furthermore, the concept of specific thermal expansion stiffness: E ^_a=E·a·A_j·h is introduced as a measure of how much thermal strain one material can induce in another.