Bobby Yang

High efficiency bifacial modules in outdoor testing

High-efficiency tunnel oxide junction cells are based on the Metal-Insulator-Semiconductor concept, which combines a tunnel oxide junction with doped a-Si thin film emitter layers on n-type CZ silicon wafers. The cells are bifacial by design and allow for almost equal power generation from the front and from the back. Packaged inside a module with transparent front and backside allows for light capture from both sides of the module in a field installation. For the first time for this tunnel oxide technology, outdoor performance and system data are presented and evaluated. The impact of climate, mounting, testing procedure and module design are studied. The results demonstrate the complexity of a bifacial outdoor system with significant yet difficult to predict performance gains over traditional module designs.

Imaging of shunts and junction breakdown in multicrystalline silicon solar cells

Recently, there has been a great deal of work investigating shunting defects in silicon solar cells. With the advancements in such techniques as DLIT, EL, and PL, shunting behavior can now be correlated to specific locations and specific defects. Shunts, which decrease device performance, are revealed under a reverse applied bias. Many of these shunts also generate a photonic emission under reverse bias, which can be observed with visible and near-IR spectrum detectors. This photonic emission or radiative recombination is often referred to as a visible breakdown emission. We investigate if each type of impurity or crystallographic defect has a unique emission spectra that can be used to identify it.