Tunnel junction limited performance of InGaAsN/GaAs tandem solar cell

Abstract From tandem solar cell we expect a wide absorption range due to different bandgaps of the subcells, higher open circuit voltage Voc and finally better photo conversion efficiency η than single junction solar cell. The main drawback of it is a current limitation i.e. the short circuit current J sc of whole structure is equal to smaller J sc of both subcells. However, even two subcells with very good photovoltaic performance do not guarantee the correct operation of tandem solar cell. The tunnel junction plays a crucial role on tandem devices as it has to provide low loss electrical and optical connection between top and bottom subcells. Within this paper we present two subcells: top GaAs based, bottom InGaAsN based with good photovoltaic performance and InGaAs tunnel diode used for InGaAsN/GaAs tandem solar cell construction. We compare reference devices with monolithic tandem cell and conclude about tunnel junction failure based on both dark and illuminated J-V characteristics of the InGaAsN/GaAs final device. Based on detailed analysis of tandem performance we propose two most likely effects responsible for tunnel junction induced deterioration of tandem solar cell performance.