Abstract
Large-area solar cells are more susceptible to imperfect surfaces, such as edges or cracks. Numerical two-dimensional methods are developed and applied to study the effects of the imperfect surface in solar cells. The two-dimensional effects investigated in this work reveal the lateral conduction of solar cells, which causes inconsistent potentials and a deviation of photocurrent. The mask effects from distributed series resistance on luminescence techniques, such as photoluminescence and electroluminescence, are also explored. Lateral conduction hides the information of the real distribution of defects, and numerical methods are applied to eliminate the effect. In multijunction solar cells, lateral conduction in the interlayer leads to the complementarity between the luminescence of top and bottom cells. Furthermore, the distributed series resistance also causes a knee in the I–V curves, resulting in a decrease in the efficiency of the cell. The research in this work demonstrates that different categories of defects show different influences on solar cells, and the effect is more obvious on the open-circuit voltage rather than the short-circuit current. The study of distributed series resistance and lateral conduction in this work not only gives an explanation of experimental data but also provides instructions for the developments of large-area solar cells.
Highlights
Energy shortage is one of the main concerns in the world, and solar energy is one of the most promising solutions for this issue
The two-dimensional circuit network by Spice6,7 has been used for solar cell simulation, the main concern lays in how defects affect the I–V curve of solar cells instead of the behavior of lateral conduction
G(A) = αI(A), where A refers to a point on the surface of the emitter of a solar cell; J is the lateral conduction current; G(A) is the generation rate at spectral flux I (A); q and α are the charge of an electron and absorption coefficient, respectively; and Rec(A, V) is the recombination rate determined by voltage V across the junction
Summary
Energy shortage is one of the main concerns in the world, and solar energy is one of the most promising solutions for this issue. High-efficiency solar cells demand high crystal quality, good spectrum-match, good Ohmic contacts, and good passivation of the surface or edges. Finger breaks, perimeter recombination, and localized defects all could influence lateral conduction and impact the shape of I–V curves.. The classic one-dimensional solar cell model has limitations in studying the influence of lateral conduction on the cell performance. The two-dimensional circuit network by Spice has been used for solar cell simulation, the main concern lays in how defects affect the I–V curve of solar cells instead of the behavior of lateral conduction. A 50 × 50 micro-solar cell network was built using MATLAB, and different kinds of two-dimensional defects, such as cracks, perimeter, or localized defects, are simulated. The connection among I–V curves, lateral conduction, and defects is built
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