Search

A new theoretical approach is proposed for the performance simulation of multijunction (MJ) solar cells, starting from the weakness and strength of the Hovel model and of the transfer matrix method for describing the propagation of electromagnetic waves inside the solar cell structure. It is based on the scattering matrix method (SMM) and on a simplified generation function that allow describing with good accuracy the propagation of electromagnetic waves in the solar cell device, preserving, at the same time, the possibility of getting simple analytical solutions of the continuity equations. The numerical stability of the new theoretical approach is first demonstrated on triple junction InGaP/InGaAs/Ge solar cells, in which the Ge substrate is considered as the last layer (layer N) and then as the N‐1 layer. Further, the new theoretical approach is applied to simulate the performance of thin quadruple junction (QJ) InGaP/InGaAs/SiGeSn/Ge solar cells, in two‐ and three‐terminal configurations. Efficiency values of up to 45.1% and 44.9%, respectively, have been simulated at 1000× concentration, by considering the MJ limited by the InGaAs subcell. Finally, it is estimated that the QJ InGaP/InGaAs/SiGeSn/Ge solar cell has the potential to reach efficiencies over 50% by assuming proper antireflective coatings. [ABSTRACT FROM AUTHOR]

In order to produce a step forward towards the monolithic integration of III-V and IV compounds in multijunction solar cells, a first assessment of SiGeSn deposition in a metal organic vapour phase epitaxy (MOVPE) chamber also used for III-V growth has been carried out. The study brings insights on several aspects of the MOVPE SiGeSn growth in order to get a better control of SiGeSn composition and to obtain epitaxial layers with improved morphology. In particular, it is shown that the gas source Si 2 H 6 is more influenced by the growth temperature compared to GeH 4 and SnCl 4 , moreover, its competition with SnCl 4 makes it difficult to incorporate Si in SiGeSn, as SnCl 4 partial pressure is increased. SiGeSn morphology is shown to be strongly dependent on temperature, As carry-over and growth rate. A new growth model is introduced in order to explain the importance of the adatom bond lengths in inhibiting tin segregation when SiGeSn is grown at relatively high growth temperatures (>480 °C). In order to investigate the photovoltaic behaviour of SiGeSn, a single-junction GaAs/InGaP/SiGeSn/Ge functional device has been manufactured and characterized by external quantum efficiency (EQE) and current-voltage measurements. The experimental and the simulated EQE show the higher absorption coefficient of SiGeSn with respect to Ge, which allows using SiGeSn layers with a thickness three times lower than Ge to produce the same photovoltaic current. Image 1 • A step forward towards the monolithic integration of III-V and IV elements in multi-junction solar cell. • New insights on MOVPE SiGeSn growth in a reactor used for III-V growth. • Discover how arsenic carry-over allows obtaining growth SiGeSn -tin segregation free- at temperature >480°C. • SiGeSn optical data, EQE and IV characterization of a GaAs/InGaP/SiGeSn/Ge functional device. [ABSTRACT FROM AUTHOR]

We have deposited Ge, SiGe, SiGeSn, AlAs, GaAs, InGaP and InGaAs based structures in the same metalorganic vapor phase epitaxy (MOVPE) growth chamber, in order to study the effect of the cross influence between groups IV and III-V elements on the growth rate, background doping and morphology. It is shown that by adopting an innovative design of the MOVPE growth chamber and proper growth condition, the IV elements growth rate penalization due to As "carry over" can be eliminated and the background doping level in both IV and III-V semiconductors can be drastically reduced. In the temperature range 748–888 K, Ge and SiGe morphologies do not degrade when the semiconductors are grown in a III-V-contaminated MOVPE growth chamber. Critical morphology aspects have been identified for SiGeSn and III-Vs, when the MOVPE deposition takes place, respectively, in a As or Sn-contaminated MOVPE growth chamber. III-Vs morphologies are influenced by substrate type and orientation. The results are promising in view of the monolithic integration of group-IV with III-V compounds in multi-junction solar cells. [ABSTRACT FROM AUTHOR]