Analysis of Thermal Behavior and Reliability of Bare Die Diodes Embedded Within PV Modules as Bypass Devices

The installation of bypass devices embedded within a photovoltaic (PV) module is an increasingly attractive option for simplifying module design and manufacturing, offering an alternative to the current standard of connecting and gluing to the laminated module one or more external boxes containing the bypass diodes. However, certain technical challenges require further exploration for a reliable integration. We analyze the role of the geometry of the diode, and of the module's bill of materials (BOM) in dissipating heat when partial shading occurs on a PV array, putting the diode in forward bias. Critical parameters for module-integrated bare die diodes are defined such that its maximum operating temperature remains below 95 degrees C. Different approaches are explored experimentally and a Finite Element Method (FEM) model is created to predict said maximum temperatures. It is found that while the chip size is one main factor in dissipating heat efficiently, other methods for modifying the geometry of the diode-connectors subassembly can aid considerably in reducing the temperature of the device during operation, all without substantially increasing the size of the semiconductor. Connecting in parallel two or more small diodes, increasing the width of the connectors, and adding flat heat sinks are some of the proposed approaches. Furthermore, performance and reliability tests are executed to understand how degradation of the integrated diodes might affect the lifetime of the PV module, showing that when operation temperatures above 130 degrees C are maintained even for a relatively short time, some degradation of the electrical contacting of the diode will occur.