# Fileset [elsarticle-template-harv.docx](https://mdr.nims.go.jp/filesets/ef4c0fd4-ec23-4308-a94c-08da68bd1c69/download) ## Creator K. Itabashi, S. Fujii, [M. Imura](https://orcid.org/0000-0002-4236-9549), T. Isobe, M. Miyahara, J. Nishinaga, H. Okumura, M. Togawa ## Rights [Creative Commons BY-NC-ND Attribution-NonCommercial-NoDerivs 4.0 International](https://creativecommons.org/licenses/by-nc-nd/4.0/) ## Other metadata [Study of radiation tolerance of Cu(In,Ga)Se 2 detector](https://mdr.nims.go.jp/datasets/f8136362-11ba-4436-97e1-361ef6b94574) ## Fulltext HighlightsStudy of radiation tolerance of Cu(In, Ga)Se2 detectorK. Itabashi, S. Fujii, M. Imura, T. Isobe, M. Miyahara, J. Nishinaga, H. Oku- mura, M. Togawa· Semiconductor detector’s performances degrade by radiation damage.· A CIGS solar cell has an ability to recover from radiation damage though thermal annealing.· The degradation of collected charge by 132Xe54+ irradiation is recovered by thermal annealing at 130 ◦C.· The recovery characteristic of radiation damage in CIGS semiconductor is also beneficial for detectors.· The recovery speed of proton irradiation damage in CIGS solar cells strongly depends on the annealing temperature.Study of radiation tolerance of Cu(In, Ga)Se2 detectorK. Itabashia, S. Fujiib, M. Imurac, T. Isobed, M. Miyaharaa,e, J. Nishinagaf,H. Okumurag, M. Togawaa,eaInternational Center for Quantum-field Measurement Systems for Studies of the Universe and Particles (QUP,WPI), High Energy Accelerator Research Organization (KEK), Oho 1-1, Tsukuba, Ibaraki 305-0801, Japan.bThe Graduate University for Advanced Studies, SOKENDAI, Kanagawa, Japan. cResearch Center for Electronic and Optical Materials, National Institute for Materials Science (NIMS), Tsukuba, Ibaraki 305-0044, Japan.dInstitute of Physical and Chemical Research (RIKEN), Wako, Sitama, 351-098, Japan. eInstitute of Particle and Nuclear Studies, High Energy Accelerator Research Organization (KEK), Tsukuba, Ibaraki 305-0801, Japan.fGlobal Zero Emission Research Center, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Ibaraki 305-8568, Japan.gFaculty of Pure and Applied Sciences, University of Tsukuba, Tsukuba, Ibaraki 305-8573, Japan.AbstractA Cu(In, Ga)Se2 (CIGS) semiconductor has been widely developed as a solar cell. It is known to have a radiation damage recovery mechanism brought about by a process of thermal annealing. We investigated the radiation dam- age recovery mechanism though two irradiation experiments at HIMAC and CYRIC. In the HIMAC experiment, a 2 µm-thick CIGS detector was irra- diated with a 400 MeV/u Xe ion (132Xe+54) beam, and the collected charge from Xe signal was observed. After Xe beam irradiation with a dose of0.6 MGy, collected charge from the Xe beam was deteriorated to 51% of initial state. However, it recovered to 97% after 2 hours dark annealing at 130 ◦C. In the CYRIC experiment, 70 MeV protons with a fluence of7.5×1015 MeV neq/cm2 were irradiated to CIGS solar cells. After dark an- nealing at 130 ◦C for 1 hour, a short circuit current density (JSC) recovered from 57% to 85% of the initial state. On the other hand, it took about 34 hours for the JSC to recover from 50% to 85% at 90 ◦C. From these two irradiation experiments, it appeared that the radiation damage recovery mechanism is effective for the CIGS detector, the amount of recovery having a strong dependence on annealing temperature.Preprint submitted to Elsevier September 3, 2024Keywords: CIGS, Radiation-hard detector, Radiation-hard solar cell1. IntroductionA Cu(In, Ga)Se2 (CIGS) is an alloy semiconductor of CuInSe2 and CuGaSe2.Since CIGS is a direct band gap semiconductor, it has a high light absorp- tion coefficient among solar cell materials and can absorb a broad spectrum of wavelengths, including in the infrared region. There has been significant activity in recent years in developing CIGS solar cells, and they attached a high energy conversion efficiency (η ∼ 20%), comparable to silicon solar cells [1]. Moreover, the CIGS solar cell is a promising candidate for space thin-film solar cells due to its light mass and high radiation tolerance [2]. In the previous experiment conducted at the Cyclotron and Radioisotope Cen- ter(CYRIC) in Tohoku University, we irradiated the 70 MeV proton beam with a fluence of 1016 MeV neq/cm2 to CIGS solar cells [3]. The short- circuit current density (JSC) and conversion efficiency were deteriorated, but gradually recovered through 95 ◦C dark annealing over an extended period. Therefore, a CIGS semiconductor has potential to be a detector with high ra- diation tolerance. To gain a more quantitative understanding of the recovery mechanism, we performed Xe ion and proton irradiation experiments: Heavy Ion Medical Accelerator in Chiba (HIMAC), and Cyclotron and Radioisotope Center (CYRIC).2. 132Xe54+ beam irradiation experiment at HIMACRadiation tolerance in CIGS detectors was studied using a 400 MeV/u Xe ion (132Xe54+) beam at HIMAC. Figure 1 (left) shows the integrated ADC value from Xe ion signal (collected charge). The collected charge from Xe ion signals continuously decreased to 50% of the initial state after Xe ion beam irradiation with 0.6 MGy. However, after 2 hours dark annealing at 130 ◦C, the collected charge recovered to 97% (Fig. 1, right). It was the first observation of radiation damage recovery in CIGS detectors, highlighting the potential for CIGS detectors with high radiation tolerance.3. 70 MeV proton irradiation experiment at CYRICIn order to investigate the recovery mechanism of radiation damage, we irradiated CIGS solar cells, which have a thickness of 2 µm, with a 70 MeV2Figure 1: Left) Integrated ADC values from the Xe ion beam. Right) The Xe ion beam irradiation time dependence of the collected charge, and the collected charge recovery by dark annealing at 130 ◦C. The relative charge value continuously decreased during 16 hours period of 132Xe54+ irradiation. After two one-hour periods of dark annealing (blue hatched area), the relative charge value recovered to 97%.proton beam at CYRIC. The annealing temperature dependence of the re- covery mechanism was evaluated through the current density-voltage (J-V) characteristic under irradiation with solar irradiation with an AM1.5 spec- trum with 100 mWcm−2 at 25 ◦C. Figure 2 (left) shows the J-V curves. The J value decreased by radiation damage with a fluence of 7.5×1015 Me Vneq/cm2 (blue line), but it recovered after dark annealing at 130 ◦C for 1.5 hours (yel- low line) and 2.5 hours (light blue line). Figure 2 (right) shows dark annealing cycles using proton irradiated solar cells heated under three different temper- ature conditions. The vertical axis represents a relative ratio of JSC, which is the J value at 0 bias voltage, to that before irradiation. After a 90-minute period of annealing at 130 ◦C, the JSC value reached saturation, the data exhibiting slight systematic fluctuations (Fig.2).After 1 hour of dark annealing at 130 ◦C, the JSC value recovered from0.57 to 0.85, and then saturated at 0.87 for 90 minutes of dark annealing. Conversely, dark annealing at 90 ◦C required a longer period for JSC to recover to 0.85 compared to dark annealing at 130 ◦C. This result is consistent with the recovery speed of collected charge measured in the HIMAC experiment at 130 ◦C (Fig. 1, right), and is expected to reflect similar trends in the CIGS detector.4. ConclusionThe recovery mechanism of CIGS have been investigated though the pro- ton and Xe beam irradiation experiments. After proton and Xe irradiation, the performance of CIGS deteriorated due to radiation damage. However, we observed a recovery in the deteriorated performance by dark annealing35hhJ [mA/cm2]7.51015 MeV n /cm2nq130 C annealing for 1.5130 C annealing for 2.5Before Irradiation3025201510500 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8Voltage [V]00.190 C annealing110 C annealing130 C annealing.98765Relative ratio of JSC0.0.0.0 200 400 600 800 1000 1200 1400 1600 1800 2000 2200Annealing time [min]Figure 2: Left) J-V curve with an AM1.5 spectrum at 100 mWcm−2 at 25 ◦C. Right) Annealing time dependence of JSC at 90, 110 and 130 ◦C.at 130 ◦C for a short period. Through dark annealing of CIGS solar cells irradiated by the proton beam with the fluence of 7.5×1015 MeV neq/cm2, we observed that the JSC recovery has strong dependence on the annealing temperature.AcknowledmentsThis work was supported by World Premier International Research Cen- ter Initiative (WPI), the Ministry of Education, Culture, Sports, Science and Technology (MEXT), Japan. This work was also supported by JSPS KAKENHI Grant No. 21K18635 and 23H01191 from MEXT, Japan and the Tsukuba Innovation Area (TIA). Part of the experiment was performed under the Research Project with Heavy Ions at NIRS-HIMAC, program No. 21H455.References[1] W. Liu et al., Solar Energy 233 337-344 (2022).[2] M. Imaizumi et al., Prog. Phot. Res. Appl. 13 529-543 (2005).[3] J. Nishinaga et al., J. Appl. Phys. 62 SK1014 (2023).image3.pngimage4.pngimage5.pngimage1.jpegimage2.png