Impact of work function of back contact of perovskite solar cells without hole transport material analyzed by device simulation

Takashi Minemoto,Masashi Murata 한국물리학회 2014 Current Applied Physics Vol.14 No.11

The impact of the work function of a metal back contact on lead methylammonium tri-iodide based perovskite solar cells without hole transport material (HTM) was analyzed using device simulation. The elimination of the HTM is attractive in terms of the simplification of device structure and fabrication process. In the solar cell, a back junction is formed by the perovskite absorber and metal back contact. The device simulation revealed that the elimination of the HTM did not change the built-in voltage (Vbi) of the device when the work function of the metal back contact (fM) was similar to the valence band maximum of the absorber (Ev_absorber). In the HTM-free structure, Vbi showed a high value if fM was equal to or deeper than Ev_absorber. In contrast, when fM was shallower than Ev_absorber, Vbi monotonically decreased, resulting in the decrease in open-circuit voltage of the device. The results showed the importance of the fM matching to maintain Vbi, which is useful guideline for the design of the HTM-free perovskite solar cells.

Outdoor performance evaluation of photovoltaic modules using contour plots

Takashi Minemoto,Hiroaki Takahashi,Yasuhito Nakada,Hideyuki Takakura 한국물리학회 2010 Current Applied Physics Vol.10 No.2

The impact of environmental parameters on different types of Si-based photovoltaic (PV) modules (single crystalline Si (sc-Si), amorphous Si (a-Si) and a-Si/ microcrystalline Si (μc-Si)) which have different spectral responses were characterized using contour plots. The contour plots of PV performance as a function of module temperature and spectral irradiance distribution were created to separate the impact of the two environmental parameters. The performance of the sc-Si PV module was dominated by the module temperature while those of a-Si and a-Si/lc-Si ones were mainly influenced by the spectral irradiance distribution. Furthermore, the frequency of outdoor conditions and the reliability of the contour plots of the PV performance were discussed for the evaluation of PV modules by means of energy production.

Cu(In,Ga)Se2 superstrate-type solar cells with Zn1−xMgxO buffer layers

Takashi Minemoto,Shinya Harada,Hideyuki Takakura 한국물리학회 2012 Current Applied Physics Vol.12 No.1

Superstrate-type Cu(In,Ga)Se2 (CIGS) thin film solar cells were fabricated using Zn1-xMgxO buffer layers. Due to the diffusion of Cd into CIGS during the growth of the CIGS layer, the conventional buffer material of CdS is not suitable. ZnO is a good candidate because of higher thermal tolerance but the conduction band offset (CBO) of ZnO/CIGS is not appropriate. In this study, the Zn1-xMgxO buffer layers were used to fulfill both the requirements. The superstrate-type solar cells with a soda-lime glass/In2O3:Sn/Zn1-xMgxO/CIGS/Au structure were fabricated with different band gap energies of the Zn1-xMgxO layer. The CIGS layers [Ga/(In + Ga)~0.25] were deposited by co-evaporation method. The substrate temperature during the CIGS deposition of 450 ℃ did not cause the intermixing of the Zn1-xMgxO and CIGS layers. The conversion efficiency of the cell with Zn1-xMgxO was higher than that with ZnO due to the improvement of open-circuit voltage and shunt resistance. The results well corresponded to the behavior of the adjustment of CBO, demonstrating that the usefulness of the Zn1-xMgxO layer for the CBO control in the superstrate-type CIGS solar cells. Superstrate-type Cu(In,Ga)Se2 (CIGS) thin film solar cells were fabricated using Zn1-xMgxO buffer layers. Due to the diffusion of Cd into CIGS during the growth of the CIGS layer, the conventional buffer material of CdS is not suitable. ZnO is a good candidate because of higher thermal tolerance but the conduction band offset (CBO) of ZnO/CIGS is not appropriate. In this study, the Zn1-xMgxO buffer layers were used to fulfill both the requirements. The superstrate-type solar cells with a soda-lime glass/In2O3:Sn/Zn1-xMgxO/CIGS/Au structure were fabricated with different band gap energies of the Zn1-xMgxO layer. The CIGS layers [Ga/(In + Ga)~0.25] were deposited by co-evaporation method. The substrate temperature during the CIGS deposition of 450 ℃ did not cause the intermixing of the Zn1-xMgxO and CIGS layers. The conversion efficiency of the cell with Zn1-xMgxO was higher than that with ZnO due to the improvement of open-circuit voltage and shunt resistance. The results well corresponded to the behavior of the adjustment of CBO, demonstrating that the usefulness of the Zn1-xMgxO layer for the CBO control in the superstrate-type CIGS solar cells.

Buffer-less Cu(In,Ga)Se2 solar cells by band offset control using novel transparent electrode

Takashi Minemoto,Jasmeen Julayhi 한국물리학회 2013 Current Applied Physics Vol.13 No.1

Cu(In,Ga)Se2 (CIGS) solar cells without buffer layers have been demonstrated. Currently, CdS, Zn(O,S,OH), ZnS, or InS buffer layers are used in high efficiency CIGS solar cells to suppress interface recombination. One of the important parameters to reduce the recombination is the conduction band offset (CBO) between the buffer and CIGS layers. In this study, we have proposed the use of a novel transparent conductive oxide (TCO) which can control the CBO to reduce interface recombination and eliminate the buffer layers. The device simulation was used to verify the effect of CBO control theoretically. Then, the novel TCO material of ZnO1xSx:Al prepared by co-sputtering of ZnO:Al2O3 and ZnS targets was fabricated to verify the CBO effect experimentally. The efficiency of a CIGS solar cell with a ZnO:Al/CIGS/Mo/sodalime glass structure, i.e. buffer-less structure using a conventional TCO, was significantly low because of severe shunting. In contrast, the use of ZnO1-xSx:Al instead of ZnO:Al increased the shunt resistance of the CIGS solar cell, resulting in higher open-circuit voltage and efficiency. The result is the first proof of the concept of the buffer-less CIGS solar cells.

TIN(II) SULFIDE SOLAR CELLS WITH OPTIMIZED GROWTH TEMPERATURE OF THIN FILM ABSORBERS

Yu Kawano,Takashi Minemoto 한국신재생에너지학회 2013 AFORE Vol.2013 No.-

Photo current metastability in Cu(In,Ga)Se2 solar cells with controlled conduction band alignment

Hiroaki Hori,Takashi Minemoto,Hideyuki Takakura 한국물리학회 2010 Current Applied Physics Vol.10 No.2

A metastability of current density–voltage characteristics, so called a light soaking (LS) effect, in (Zn,Mg)O (ZMO)/Cu(In,Ga)Se2 (CIGS) solar cells with the controlled conduction band offset (CBO) between window and CIGS layers was measured. The strong LS effect was observed with increasing the CBO value from +0.03 eV to +0.35 eV. Here, plus sign of CBO indicate the conduction band minimums of the window layers above that of the CIGS layers. When the CBO is positive, the CBO acts as a barrier for photo-generated electrons in the CIGS layer. On the other hand, the CIGS solar cells with Cd partial electrolyte treatment for the CIGS surface before the ZMO deposition showed the negligible LS effect. These results indicate that the LS effect would relate to the photo current which is affected by CBO and surface condition of the CIGS film, and the external quantum efficiency measurements support this hypothesis.

IMPACT OF ZN<SUB>1-x</SUB>MG<SUB>x</SUB>O:AL TRANSPARENT ELECTRODE FOR BUFFER-LESS CU(IN,GA)SE₂ SOLAR CELLS

Yoshihiro Kuwahata,Takashi Minemoto 한국신재생에너지학회 2012 AFORE Vol.2012 No.-

Photovoltaic measurements on Cu(In,Ga)Se₂ solar cells by photo-assisted Kelvin probe force microscopy

Hyeondeuk YONG,Takashi MINEMOTO,Takuji TAKAHASHI 한국진공학회 2016 한국진공학회 학술발표회초록집 Vol.2016 No.8

Impact of growth temperature on the properties of SnS film prepared by thermal evaporation and its photovoltaic performance

Yu Kawano,Jakapan Chantana,Takashi Minemoto 한국물리학회 2015 Current Applied Physics Vol.15 No.8

Tin(II) sulfide (SnS) films are one of the most promising absorber materials for high efficiency solar cells without using rare metals. In this work, SnS films were deposited by the thermal evaporation on glass substrates under the variation of growth temperatures of 100-250 ℃. It was revealed that the SnS thin film prepared under the temperature of 100 ℃ had relatively small crystal grains. On the other hand, the denser and larger crystal grains of the SnS films were obtained with the constant compositions, when the growth temperature increased to 225 ℃. With the temperature of higher than 225 ℃, the SnS began to be re-evaporated from the films. The highest Hall mobility of the films was obtained under the temperature of 200 ℃. Ultimately, the results suggested that the optimized growth temperature of SnS by the evaporation is 200 ℃, giving rise to compact and large crystal grains and the highest Hall mobility, thereby contributing to the 2.53%-efficient SnS thin-film solar cell.

Improvement of Cu2ZnSnS4 thin film morphology using Cu-Zn-Sn-O precursor fabricated by sputtering

Ryo Ishino,Kazuhiro Fukushima,Takashi Minemoto 한국물리학회 2013 Current Applied Physics Vol.13 No.9

The new precursor of CueZneSneO (CZTO) was proposed for Cu2ZnSnS4 (CZTS) thin film fabrication to improve film morphology. The CZTS thin film grown from CueZneSn (CZT) precursors has many bumps. We deposited CZTO precursors on Mo/soda-lime glass (SLG) substrates by RF sputtering using a CZT (Cu:Zn:Sn ¼ 2:1:1) target in Ar and O2 atmosphere at various O2 partial pressures (0%, 5%, 17% and 20%). Subsequently, the CZTO precursors were sulfurized in Ar and S atmosphere to fabricate CZTS thin films. The CZTO precursors were amorphous. The morphology of the CZTS thin films was improved by the CZTO precursors. All of the CZTS films fabricated in this study had the same crystal structure. Composition analysis revealed that 50% of O were detected in the CZTO precursor, but O was not detected after sulfurizing process, indicating that O was substituted by S. The CZTS thin film from the CZTO precursor fabricated at O2 partial pressure of 20% had similar composition for solar cell absorber.