Microcracks in Silicon Wafers II: Implications on Solar Cell Characteristics, Statistics and Physical Origin

Abstract

Microcracks that are induced in early processing stages, especially before emitter diffusion, strongly influence the current-voltage (I−V ) characteristics of the solar cell. We focus on the impact of crack morphology measured by photoluminescence imaging in the as-cut stage on the electrical solar cell parameters. To provide a sufficient statistical base, microcracks are intentionally induced in a well-defined way in multi-(mc-Si) and mono-(Cz-Si) crystalline silicon wafers in the as-cut stage, the damaged wafers being processed to solar cells afterwards. From the dataset, a sorting criterion for microcracks concerning their electrical impact is derived, which depends on wafer thickness and material type. It is shown that cracks above 4 mm 2 lead with high probability to severe shunts and, thus, need to be sorted out. Investigations by means of scanning electron microscopy (SEM) and electron-beam induced current (EBIC) measurements reveal that shunts with very low parallel resistance in Cz-Si solar cells can be attributed to metal-to-metal contacts between front and rear sides of the solar cell. Moreover, it is shown that the reduced robustness of Cz-Si compared with mc-Si concerning the formation of shunts at microcracks originates from a widening of the crack channels above 10 μm in alkaline texturing, which facilitates the formation of metal-to-metal contacts.

Deep learning‐based automatic detection of multitype defects in photovoltaic modules and application in real production line

“…These defects were collected from one factory, and other companies may have a few different types due to distinction of manufacturing technology. In addition, part of our defects can also be found in some literatures, 2,25–27 although they may have different names. To our knowledge, except for crack, finger interruption and break that other researchers used to study, the rest of our defects were barely investigated in automatic detection in literature.…”

Thermo-mechanical behavior assessment of smart wire connected and busbarPV modules during production, transportation, and subsequent field loading stages

“…The thermo-mechanical behavior of busbar PV module during manufacturing and subsequent life stages has been investigated in these studies: manufacturing process is analyzed by studies [9][10][11][12][13][14][15][16]; cracking effect on output or behavior is analyzed by studies [17][18][19][20][21][22]; behavior during application of different kind of loads is analyzed by studies [1,13,[21][22][23][24][25][26][27][28]. However, the existing studies did not include the initial stresses or pre-stresses in their analysis except studies [9,11,16], but they [9,11,16] studied production stage only.…”

Microcracks in Silicon Wafers I: Inline Detection and Implications of Crack Morphology on Wafer Strength

“…PL-images. Further, the crack does not connect the front and backside of the wafer for the full crack length, as presented in microscopic images in [7] and [10]. In addition, a potential effect of crossing crack structures on fracture strength is neglected.…”

“…In this study, we focus on the development of powerful algorithms for an inline detection of microcracks and relate the mechanical strength of the wafers to the morphology of the most critical crack to derive a reliable classification scheme of cracks. The classification of cracks regarding the electrical quality of the resulting solar cell is presented in a parallel study in [7].…”