Abstract
An analytical model for illuminated p-i-n structures such as Solar Cells and related devices has been developed. Starting from the semiconductor equations in their most general form, and introducing assumptions for the recombination and electrical field functions, it is aimed at modelling not only the collection of photogenerated carriers but all transport mechanisms such as carrier drift and diffusion. Using this model, the behaviour of thin film cells which is observed in operation is described in detail. This includes the dependencies of I/V curves on temperature, insolation and spectral effects, and electronic materials properties. The modeling of recombination effects results in a voltage dependent photocurrent where the carrier collection efficiency depends on the bias voltage. This model allows for relatively fast calculation of I/V curves as it is computationally less extensive than full device numerical simulations. Therefore it may be applicable for compact models i.e. in solar cell performance modelling.
Highlights
Analytical Modelling of semiconductor devices often provides highly useful insights into the underlying physics
As the semiconductor equations in their general form are complex, they are solvable in closed form only when simplifications are introduced into the equation system
A new model for the description of p-i-n structures has been presented that is focusing on the charge carrier densities and transport processes within the intrinsic layer
Summary
Analytical Modelling of semiconductor devices often provides highly useful insights into the underlying physics. Being focused on minority carriers, the Shockley model does not couple the transport equations of majority and minority carriers and it cannot properly describe recombination in the space charge region where concentrations of both carrier types are in the same order of magnitude As this applies in the same manner for the most part of the i-layer, the Shockley diode equation is not well suited for describing p-i-n devices in general. The model calculates the dominant transport mechanisms, depending on the depth in the i-layer It shows a diode-like behaviour including a reverse saturation current as much as deviations from the “ideal” diode I/V characteristics, and a voltage dependent photocurrent.
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