Calculation of the position-dependent inner collection efficiency in PIN solar cells using an electrical–optical model

The position-dependent inner collection efficiency (PDICE) is defined as the probability for an electron–hole pair generated at a certain depth inside a solar cell to be collected. The quantum efficiency (QE) of a PIN solar cell yields the I-layer carrier collection probability as a function of the wavelength, whence only a crude idea of its position dependence can be obtained. Hence for optimizing carrier collection within the intrinsic layer, knowledge of its PDICE is also important. So far PDICE has been calculated by matrix inversion from external QE measurements, a procedure that leads to non-physical oscillations. In this report we determine PDICE in thin film solar cells using our electrical–optical model, which solves the Poissonʹs equation and the continuity equations. Our method requires the simulation of a large number of experimental results, from which the parameters reproducing the characteristics of a given device are extracted. These parameters are then used to calculate PDICE. To the best of our knowledge this is the first time that such a model has been used to calculate PDICE. We next apply the method to calculate PDICE in PIN solar cells prepared under various conditions.