High efficiency Cu(In,Ga)Se/sub 2/-based solar cells: processing of novel absorber structures

Abstract

Our effort towards the attainment of high performance devices has yielded several devices with total-area conversion efficiencies above 16%, the highest measuring 16.8% under standard reporting conditions (ASTM E892-87, Global 1000 W/m'). The first attempts to translate this development to larger areas resulted in an efficiency of 12.5% for a 1 6.8-cm2 monolithically interconnected submodule test structure, and 15.3% for a 4.85-cm' single cell. Achievement of a 17.2% device efficiency fabricated for operation under concentration (22-sun) is also reported. All high efficiency devices reported here are made from graded bandgap absorbers. Bandgap grading is achieved by compositional Ga/(ln+Ga) profiling as a function of depth. The fabrication schemes to achieve the graded absorbers, the window materials and contacting will be described.

Deposition Technologies of High-Efficiency CIGS Solar Cells: Development of Two-Step and Co-Evaporation Processes

“…With similar GGI ratios for the CIGS films deposited by the co-evaporation processes, the corresponding bandgap energies are nearly the same. Nevertheless, the CIGS films prepared by the three-stage process had a double grading bandgap structure, meaning that the bandgap energies at the notch point of the V-shape grading structure had lower values than the effective optical bandgap energies [35][36][37]. Thus, the absorption edge of the CIGS films prepared by the three-stage process extended to the longer wavelengths than those of the films prepared by the other evaporation processes, as shown in Figure 7.…”

Development of Flexible Cu(In,Ga)Se2 Thin Film Solar Cell by Lift-Off Process

“…5(a), the band gap profile of the standard solar cell consists of the graded band gap structure because of the three-stage deposition process. The diffusion length of electrons generated by the long wavelength light near the back electrode is improved due to the quasi-electric field in which the CIGS layer forms (Contreras et al, 1994b). The graded band gap structure is therefore beneficial for collecting the photogenerated carriers.…”

How the Starting Precursor Influences the Properties of Polycrystalline CuInGaSe2 Thin Films Prepared by Sputtering and Selenization

“…In particular, an accurately tailored double-graded Ga concentration may allow for the engineering of a specific energy gap (E G ) design ( Figure 4). If this design is followed, a back grading will provide an additional drift field for the minority electrons, and this will in turn improve carrier collection and reduce back-contact recombination [8][9][10]. A second Ga grading will appear near the CIGS/CdS interface where the Ga concentration will be made higher towards the p-n junction.…”