0.74/0.55-eV Ga/sub x/In/sub 1-x/As/InAsP/sub 1-y/ monolithic, tandem, MIM TPV converters: design, growth, processing and performance

Abstract

Thermophotovoltaic (TPV) tandem converter technology is being explored in an effort to improve both the efficiency and power density of TPV systems. Inverted, tandem structures incorporate epitaxially grown 0.74-eV latticematched Gadn0.53As and 0.55-eV lattice-mismatched Gao.2alno.72As diodes. Adddionally, a strategy has been developed to allow voltage matching between these two subcells. Performance modeling calculations show that, under typical operating conditions, the 0.74/0.55eV tandem converter should outperform a 0.55-eV single junction converter by 15% on an efficiency basis and by 15% on a power density basis. This paper will present details regarding the design, growth, fabrication, and electrical, optical. and structural characterization of voltage-matched tandem TPV devices.

Monolithic interconnected modules (MIM) for high irradiance photovoltaic energy conversion: A comprehensive review

“…The results presented in [133] show a FF of 50% (and a J SC =0.7 A/cm 2 ) for the 0.55 eV cells and a FF of 65% (and a J SC =0.2 A/cm 2 ) for the 0.75 eV cells. The isolation provided by the diode was sufficiently good, achieving leakage currents below 2 mA/cm 2 for voltages comprised between -6.2 V and 8.8 V.…”

“…One of the alternatives is the use of CID isolation, i.e. reverse p-n junction isolation, as the one patented by Wanlass in [132] and used by Wherer in [133] (see "GaAs-based MIMs" section).…”

“…In 2002, Wherer and Wanlass [133] respectively from Bechtel Bettis Inc. and NREL, in collaboration with NASA and Emcore, started the development of MIM devices for TPV applications. These devices incorporated a tandem configuration with InGaAs subcells latticematched to InP (of 0.74 eV) and another lower bandgap InGaAs cell (of 0.55 eV) with a considerable lattice-mismatch with respect to the InP substrate.…”

“…In the configuration proposed by Wherer [133], the fabrication of the epitaxial structure requires that the lattice-matched 0.74 eV subcell is grown prior to the buffer layers meant to adapt the lattice constant of the crystal to the 0.55 eV subcell. Such scheme requires the use of an inverted structure, i.e.…”

“…For that purpose, in [133] the authors employ a CID adopted from the previous design by Wanlass [120,132]. The electrical isolation strategy based on a CID consists of an n/p/n structure (where the p-region is lightly doped and the n-regions have a relatively high doping) that prevents current leakages from the subcells of a tandem structure.…”