Characterization and modeling of reverse‐bias breakdown in Cu(In,Ga)Se₂ photovoltaic devices

Abstract

Partial shading of series‐connected thin‐film photovoltaic modules can force shaded cells into reverse bias, which can cause rapid and irreversible power loss and reduce the practical module lifespan. Unfortunately, this is a common occurrence in field‐deployed modules due to the myriad of environmental factors that can result in partial shading. In this work, we identify as‐grown nonuniformities in the Cu(In,Ga)Se2 (CIGS) absorber layers as the points of origin for the damage induced under reverse‐bias conditions. The structure and chemistry associated with inclusions and voids in the CIGS films cause these features to act as resistive heating elements in reverse‐bias conditions. This localized resistive heating provides the energy required to induce thermal runaway breakdown in the CIGS devices, resulting in damage to charge collection and reduced active area of a device. This mechanism is also described with a robust device model to connect the experimental observations with their physical origins.

Propagation mechanism of reverse bias induced defects in Cu(In,Ga)Se2 solar cells

“…The current limit of 100 mA was selected because it is the current generated in approximately 3 cm 2 of a neighboring cell that is fully illuminated. Furthermore, this value is in the range of currents (30 -100 mA) observed during the formation of wormlike by Guthrey et al [6].…”

“…The defect in Figure 4 (a) seems to have originated at the border where the CIGS was mechanically removed (P3 analogue) at the right side of the picture. Several studies [4][5][6][7] showed that wormlike defects originate at local weak spots. A mechanically defined edge could be a local weak spot; though, only 3 out of 8 wormlike defects started at a mechanically defined edge.…”

“…Reverse bias induced defects act as local shunts, permanently reducing the module output. These defects originate in local weak spots [4][5][6][7] and can be formed relatively easy when no mitigation measures are in place. For example by shades cast from humans or tools [8,9].…”

Влияние Воздействия Обратным Смещением На Параметры Солнечных Элементов На Основе Cigs

“…Локальные дефекты от обратного смещения в модулях CIGS часто оптически видимы и имеют вид «червячного следа» [13,14]. Эти дефекты возникают в локальных слабых местах [15,16] и относительно легко распространяются, если не принять меры. Дефекты могут возникать даже за счет тени людей или инструментов при осмотре или очистке панелей [17,18] и могут в стандартных условиях испытаний (STC) вызывать уменьшение максимальной мощности на 10% и более 30% соответственно в случае тени от человека и инструментов для чистки [19].…”

From Modules to Atoms: Techniques and Characterization for Identifying and Understanding Device-Level Photovoltaic Degradation Mechanisms

“…Figure 39(b) shows the simulated current density-voltage (J-V) curves for a cell in an ambient temperature of T = 293 K, and 1-sun light. Shunt-induced heating of the cell causes significant Voc loss[68].…”