Thin film photovoltaics (TFPV) offer low cost alternatives to conventional crystalline Silicon (c-Si) PV, and can enable novel applications of PV technology. Their large scale adoption however, requires significant improvements in process yield, and operational reliability. In order to address these challenges, comprehensive understanding of factors affecting panel yield, and predictive models of performance reliability are needed. This has proved to be especially challenging for TFPV for two reasons in particular. First, TFPV technologies encompass a wide variety of materials, processes, and structures, which fragments the research effort. Moreover, the monolithic manufacturing of TFPV modules differs significantly from that of c-Si technology, and requires new integrated approaches to analysis and design for these technologies.
In this thesis, we identify a number of features affecting the variability and reliability of TFPV technologies in general, and propose technology agnostic design solutions for improved performance, yield, and lifetime of TFPV models. We first discuss the universal features of current conduction in TFPV cells, for both intrinsic dark and light currents, and parasitic (shunt) leakage. We establish the universal physics of space-charge-limited shunt conduction in TFPV technologies, and develop physics based compact model for TFPV cells. We examine the statistics of parasitic shunting, and demonstrate its universal log-normal distribution across different technologies. We also evaluate the degradation behavior of cells under reverse bias stress, and identify different degradation mechanisms for intrinsic and parasitic components.
We then embed the physics and statistics of cell operation and degradation, in a circuit simulation framework to analyze module performance and reliability. With this integrated circuit-device simulation, we establish log-normal shunt statistics as a major cause of module efficiency loss in TFPV, and develop an in-line technique for module efficiency and yield enhancement. Finally, we study the features of TFPV module reliability under partial shading using this circuit simulation, and propose a geometrical design solution for shade tolerant TFPV modules.
The most important theme of this thesis is to establish that TFPV technologies share many universal performance, variability, and reliability challenges. And, by using a technology agnostic approach for studying these problems, we can achieve fruitful cross coupling of ideas and enable broadly applicable solutions for important technological challenges in TFPV.