Hydrogenated indium oxide window layers for high-efficiency Cu(In,Ga)Se_2 solar cells

摘要

High mobility hydrogenated indium oxide is investigated as a transparent contact for thin film Cu(In,Ga)Se_2 (CIGS) solar cells. Hydrogen doping of In_2O_3 thin films is achieved by injection of H_2O water vapor or H_2 gas during the sputter process. As-deposited amorphous In_2O_3:H films exhibit a high electron mobility of ～50 cm~2/Vs at room temperature. A bulk hydrogen concentration of ～4 at. % was measured for both optimized H-2O and H_2-processed films, although the H_2O-derived film exhibits a doping gradient as detected by elastic recoil detection analysis. Amorphous IOH films are implemented as front contacts in CIGS based solar cells, and their performance is compared with the reference ZnO:Al electrodes. The most significant feature of IOH containing devices is an enhanced open circuit voltage (V_(OC)) of ～20 mV regardless of the doping approach, whereas the short circuit current and fill factor remain the same for the H_2O case or slightly decrease for H2. The overall power conversion efficiency is improved from 15.7% to 16.2% by substituting ZnO:Al with IOH (H_2O) as front contacts. Finally, stability tests of non-encapsulated solar cells in dry air at 80 ℃ and constant illumination for 500 h demonstrate a higher stability for IOH-containing devices.