A Well-Controlled PSG Layer on Silicon Solar Cells against Potential Induced Degradation

Abstract

This study proposes a promising silicon (Si) solar cell structure for reducing the potential induced degradation (PID) of crystalline Si solar cells. Phosphorous silicate glass (PSG) layers were carefully designed on an emitter layer, and the thickness of these layers (d PSG ) was controlled by adjusting the diffusion temperature and time. The results show that the power loss remarkably decreased from 31% (d PSG = 0 nm) to 11% (d PSG = 22.3 nm) and further decreased to less than 5% after a 48-h PID test when d PSG In recent years, the number of large photovoltaic (PV) systems for generating high electricity has increased. Such PV systems contain numerous high power PV modules. Therefore, the durability of a PV module is imperative.1 The potential induced degradation (PID) of crystalline silicon (Si) solar cells, first observed by Sunpower in 2005, has drawn considerable attention in recent years. [2][3][4][5][6] This is because the local electrical short-circuiting of the pn-junction in a Si solar cell occurs under high voltage stress, which leads to a substantial reduction in the power of a module. 7Several approaches can be used to prevent PID from cell to module levels. For example, leakage current can be reduced by changing the cover glass and encapsulation materials. [8][9][10] However, applying these approaches increases the cost drastically and may cause the efficiency of solar cells to deteriorate. The soda-lime cover glass and ethylene vinyl acetate (EVA) are still the most widely used and low-cost packaging materials for solar modules. Strong demand has necessitated the modification of the antireflective layers or emitter layers in PID-resistant solar cells. However, risks should be noticed that an efficiency of a solar cell and throughput may be reduced.This study proposes a promising Si solar cell structure for reducing the PID of solar cells without influencing their efficiency and throughput. Phosphorous silicate glass (PSG) layers were carefully designed on an emitter layer to determine how they affect the efficiencies of solar cells before and after PID. A current-voltage (I-V) tester was used to determine PV parameters. An ellipseometer and transmission electron microscope (TEM) were used to measure the thicknesses of the PSG layers. Secondary ion mass spectrometry (SIMS) was used to obtain concentration profiles of Si, sodium (Na), phosphorus (P), oxygen, and nitrogen. Figure 1 shows the process flow in this study as well as the structure of a solar cell with a PSG layer. Solar-grade and monocrystalline Si wafers with a size and resistivity of 5 in 2 and 0.5-3.0 ·cm, respectively, were used in this study. These wafers were processed using the following procedures: texturization by using an alkaline solution, P diffusion by using POCl 3 as a precursor, removing PSG layers by using a dilute HF solution (for standard solar cells only), depositing SixNy films as antireflection coatings by using a plasma enhanced chemical vapor deposition, and forming front and rear contacts by performing screen-p...

Mechanistic Understanding of Polarization‐Type Potential‐Induced Degradation in Crystalline‐Silicon Photovoltaic Cell Modules

“…[30,35] However, such SiO 2 mitigates degradation for shunting-type PID. [37][38][39] This difference implies that the mechanisms of polarization-type PID and shunting-type PID are fundamentally different from one another.…”

Potential-induced degradation phenomena in single-encapsulation crystalline Si photovoltaic modules

“…With this module, only the light-receiving side of the solar cell, i.e. the anti-reflection coating, which is more important for generating the PID phenomena, 3,12,[22][23][24][25][26][27][28][29][30] is encapsulated during the PV module fabrication. The single-encapsulation module can be analyzed directly after PID testing because the nonlight-receiving side of the module is in the air and because no pre-processing is required for micro-analyses of the PID phenomena of the whole cell.…”

Behavior of the potential-induced degradation of photovoltaic modules fabricated using flat mono-crystalline silicon cells with different surface orientations

“…Hara et al 24) have reported that TiO 2 thin films deposited on the inner surfaces of a cover glass can prevent PID for c-Si modules. Du et al 25) have shown that the PID of c-Si solar cells can be effectively reduced without influencing their efficiency by inserting phosphorus silicate glass (PSG) layers between the front n + emitters and the SiN x ARC layers. PID-affected modules can recover from the degradation by applying a positive bias.…”