Solar cell efficiency, diode factor and interface recombination: insights from photoluminescence

TL;DR

This study investigates how defects, doping, and recombination mechanisms affect solar cell efficiency, using photoluminescence to quantify parameter changes and identify strategies to improve performance.

Contribution

It provides new insights into the influence of interface recombination and doping on diode factor and efficiency, supported by measurements and simulations.

Findings

Backside recombination significantly reduces open circuit voltage.

Passivation techniques effectively mitigate backside recombination effects.

Higher doping levels improve diode factor and voltage.

Abstract

Metastable defects can decisively influence the diode factor and thus the efficiency of a solar cell. The diode factor is also influenced by the doping level and the recombination mechanisms in the solar cell. Here we quantify how the various parameters change the diode factor by photoluminescence measurements and simulations. In addition, we show that backside recombination reduces the open circuit voltage in CuInSe2 solar cells by more than 40 mV. Passivation by a Ga gradient is shown to be as efficient as a passivation by dielectric layers. Increased backside recombination reduces the diode factor, not because of less metastable defect transformation but because of a sublinear increase in photo generated carriers with excitation. This reduction in diode factor is unwanted, since the increased recombination reduces the voltage. A higher doping level, on the other hand, reduces the diode factor, thereby increasing the fill factor, and at the same time increases the voltage.