Improved Efficiency of a Large-Area Cu(In,Ga)Se₂ Solar Cell by a Nontoxic Hydrogen-Assisted Solid Se Vapor Selenization Process

Abstract

A nontoxic hydrogen-assisted solid Se vapor selenization process (HASVS) technique to achieve a large-area (40 × 30 cm(2)) Cu(In,Ga)Se2 (CIGS) solar panel with enhanced efficiencies from 7.1 to 10.8% (12.0% for active area) was demonstrated. The remarkable improvement of efficiency and fill factor comes from improved open circuit voltage (Voc) and reduced dark current due to (1) decreased interface recombination raised from the formation of a widened buried homojunction with n-type Cd(Cu) participation and (2) enhanced separation of electron and hole carriers resulting from the accumulation of Na atoms on the surface of the CIGS film. The effects of microstructural, compositional, and electrical characteristics with hydrogen-assisted Se vapor selenization, including interdiffusion of atoms and formation of buried homojunction, were examined in detail. This methodology can be also applied to CIS (CuInSe2) thin film solar cells with enhanced efficiencies from 5.3% to 8.5% (9.4% for active area) and provides a facile approach to improve quality of CIGS and stimulate the nontoxic progress in the large scale CIGS PV industry.

Adjusting the Ga grading during fast atmospheric processing of Cu(In,Ga)Se2 solar cell absorber layers using elemental selenium vapor

“…Schöppe et al [20] only recently reported that they have been able to obtain a constant Ga concentration throughout the absorber by applying a stepwise selenization process, with an intermediate selenization stage at a substrate temperature of 390°C and a process duration of >20 min in their vacuum system. Similarly, Wu et al [21,22] recently described a hydrogen assisted selenization (>20 min) process under 80 Torr N 2 pressure, where the Ga grading is more moderate, especially after an intermediate annealing stage without Se at 330°C.…”

Coatings for Energy Applications

“…They had reported the enhancement in the efficiency from 7.1 % to 10.8 % for this particular type of solar cells [9]. Enhanced efficiency is contributed to the decrease in buffer layer (Cd)/CIGS the interface recombination and the enhanced separation of electron and hole carriers by the back surface field on the surface of the CIGS film [9].…”

“…These limitations had led to the second generation of thin film-based solar cells, where varieties of thin film were established for different purposes. Several researchers have reported the thin film solar cell of silicon (Si) type [8], cadmium telluride (CdTe), copper indium selenide (CIS), copper zinc tin sulphide (CZTS), and copper indium gallium selenide (CIGS) [9]. Lee et al had coated a layer of ZnO as anti-reflecting coatings, which enhances the efficiency of solar cells [10].…”

Review on Substrate and Molybdenum Back Contact in CIGS Thin Film Solar Cell

“…International Journal of Photoenergy conditions [120][121][122]. The quality of the Mo crystals improves with sputtering power, thereby reducing the resistance of the Mo back contact.…”