Temperature dependent external quantum efficiency simulations and experimental measurement of lattice matched quantum dot enhanced multi-junction solar cells

The external quantum efficiency (EQE) of a high efficiency lattice matched multi-junction solar cell (MJSC) and a quantum dot enhanced MJSC are numerically simulated. An effective medium is developed and integrated into the model to simulate the absorption characteristics of the quantum dots in the latter device. A calibration of the model is carried out using room temperature EQE measurements of both MJSC designs. The numerical model is further generalized through the development of a novel temperature dependent absorption model based on the Varshni relation for bandgap narrowing due to temperature. Integrating this model into the numerical simulation environment accurately reproduced the experimentally observed shifts in the EQE edge of each sub-cell as a function of temperature, including the shift in the quantum dot peak. The current - voltage characteristics are discussed under the AM1.5D spectrum for concentrated illumination and realistic temperatures in concentrator systems. The development of this temperature dependent absorption model is an important addition to the set of design tools used to optimize high efficiency MJSC under realistic temperatures and spectral conditions experienced in concentrated photovoltaic systems.