Latest developments in CdTe, CuInGaSe2 and GaAs/AlGaAs thin film PV solar cells

I.M. Dharmadasa 한국물리학회 2009 Current Applied Physics Vol.9 No.2

This paper summarises the latest developments in thin film solar cells based on CdTe, CuInGaSe2 and GaAs/AlGaAs absorber materials. After proposing a new model for CdS/CdTe solar cells, new designs based on graded bandgap multi-layer solar cells have been proposed for photovoltaic (PV) solar cell development. These new designs have been tested with well researched materials, GaAs/AlGaAs, and highest open circuit voltages of 1170 mV and fill factors of ~0.85 values were produced for initial growths and fabrications. This work has led to the identification of disadvantages of the tunnel junction approach, in the present manufacturing process. Recently, it has been shown that Fermi level pinning takes place at one of the four experimentally observed defect levels in CuInGaSe2/metal interfaces very similar to that of CdTe/metal contacts. These levels are at 0.77, 0.84, 0.93 and 1.03 eV with ±0.02 eV error and are situated above the valence band maximum. As a result, discrete values of open circuit voltages are observed and the situation is very similar to that of CdS/CdTe solar cells. It is becoming clear that Fermi level pinning due to defect levels dominates the performance in at least CdTe and CIGS thin film devices and future research should be directed to solving associated issues and hence improving the performance of PV solar cells. This paper summarises the latest developments in thin film solar cells based on CdTe, CuInGaSe2 and GaAs/AlGaAs absorber materials. After proposing a new model for CdS/CdTe solar cells, new designs based on graded bandgap multi-layer solar cells have been proposed for photovoltaic (PV) solar cell development. These new designs have been tested with well researched materials, GaAs/AlGaAs, and highest open circuit voltages of 1170 mV and fill factors of ~0.85 values were produced for initial growths and fabrications. This work has led to the identification of disadvantages of the tunnel junction approach, in the present manufacturing process. Recently, it has been shown that Fermi level pinning takes place at one of the four experimentally observed defect levels in CuInGaSe2/metal interfaces very similar to that of CdTe/metal contacts. These levels are at 0.77, 0.84, 0.93 and 1.03 eV with ±0.02 eV error and are situated above the valence band maximum. As a result, discrete values of open circuit voltages are observed and the situation is very similar to that of CdS/CdTe solar cells. It is becoming clear that Fermi level pinning due to defect levels dominates the performance in at least CdTe and CIGS thin film devices and future research should be directed to solving associated issues and hence improving the performance of PV solar cells.

Increase in conversion efficiency of above 14% in Cu(In,Ga)₃Se₅ (β-CIGS) solar cells by Na₂S incorporation through the surface of β –CIGS film

Kim, Ji Hye,Kim, Seung Tae,Larina, Liudmila,Ahn, Byung Tae,Kim, KiHwan,Yun, Jae Ho Elsevier 2018 Solar energy materials and solar cells Vol.179 No.-

<P><B>Abstract</B></P> <P>Little work has been reported on the performance improvement of the β-CIGS solar cell itself even though the β-CIGS phase can have an ideal band gap for high-conversion efficiency solar cells. We incorporated Na<SUB>2</SUB>S to β-CIGS film by supplying Na<SUB>2</SUB>S to three different stages: on the (In,Ga)<SUB>2</SUB>Se<SUB>3</SUB> layer, on the α-CIGS layer, and on the β -CIGS layer in the three-stage co-evaporation process. The purpose of Na<SUB>2</SUB>S incorporation was to control the carrier concentration and passivate grain boundaries in β–CIGS film. With Na<SUB>2</SUB>S incorporation on the β–CIGS surface, both the Cu and Se concentrations at the β–CIGS surface were greatly reduced and the Na-depleted subsurface area that existed in the referenced β–CIGS film without Na<SUB>2</SUB>S was eliminated. The carrier concentration determined at 100kHz was lowest with Na<SUB>2</SUB>S incorporation on the β–CIGS surface, while that determined at 1MHz was similar with various Na<SUB>2</SUB>S supply stages. The open-circuit voltage and fill factor greatly increased in the β–CIGS solar cell with the Na<SUB>2</SUB>S incorporation. The cell conversion efficiency with Na<SUB>2</SUB>S incorporation on the β-CIGS layer improved from 10.3% to 14.2% without AR coating, which is a record efficiency in β-CIGS solar cells at this time.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The performance of Cu(In,Ga)<SUB>3</SUB>Se<SUB>5</SUB> (β-CIGS) solar cell was improved by Na<SUB>2</SUB>S doping. </LI> <LI> Na<SUB>2</SUB>S was supplied on the surfaces of (In,Ga)<SUB>2</SUB>Se<SUB>3</SUB>, α-CIGS layer, and β -CIGS layers. </LI> <LI> Na<SUB>2</SUB>S on the β–CIGS surface reduced both the Cu and Se concentrations at the surface. </LI> <LI> Na<SUB>2</SUB>S on the β–CIGS surface eliminated the Na depletion zone in the CIGS film. </LI> <LI> The cell conversion efficiency improved from 10.3% to 14.2% without AR coating. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>(a) A schematic three-stage co-evaporation process for Cu(In,Ga)<SUB>3</SUB>Se<SUB>5</SUB> (β-CIGS) film with Na<SUB>2</SUB>S incorporation at various stages and (b) J-V curves of the β–CIGS solar cell with the best efficiency of 14.2% without antireflective coating by Na<SUB>2</SUB>S incorporation on the β–CIGS layer (③).</P> <P>[DISPLAY OMISSION]</P>

Study of ZnS/CIGS Hetero-interface for Cd-free CIGS Solar Cells

신동협(Shin, Donghyeop),김지혜(Kim, Jihye),고영민(Go, Youngmin),윤재호(Yun, Jaeho),안병태(Ahn, Byungtae) 한국신재생에너지학회 2011 한국신재생에너지학회 학술대회논문집 Vol.2011 No.05

The Cu(In,Ga)Se2 (CIGS) thin film solar cells have been achieved until almost 20% efficiency by NREL. These solar cells include chemically deposited CdS as buffer layer between CIGS absorber layer and ZnO window layer. Although CIGS solar cells with CdS buffer layer show excellent performance, the short wavelength response of CIGS solar cell is limited by narrow CdS band gap of about 2.42 eV. Taking into consideration the environmental aspect, the toxic Cd element should be replaced by a different material. Among Cd-free candidate materials, the CIGS thin film solar cells with ZnS buffer layer seem to be promising with 17.2%(module by showa shell K.K.), 18.6%(small area by NREL). However, ZnS/CIGS solar cells still show lower performance than CdS/CIGS solar cells. There are several reported reasons to reduce the efficiency of ZnS/CIGS solar cells. Nakada reported ZnS thin film had many defects such as stacking faults, pin-holes, so that crytallinity of ZnS thin film is poor, compared to CdS thin film. Additionally, it was known that the hetero-interface between ZnS and CIGS layer made unfavorable band alignment. The unfavorable band alignment hinders electron transport at the heteo-interface. In this study, we focused on growing defect-free ZnS thin film and for favorable band alignment of ZnS/CIGS, bandgap of ZnS and CIGS, valece band structure of ZnS/CIGS were modified. Finally, we verified the photovoltaic properties of ZnS/CIGS solar cells.

Improving Performance of CIGS Thin Film Solar Cell via Optimization of CdS/CIGS p-n Junction : pH Control of CBD Bath

김다슬,민병권 한국공업화학회 2019 한국공업화학회 연구논문 초록집 Vol.2019 No.1

For CIGS thin film solar cells, design of p-n junction is crucial because it is closely related to both generation and collection of photo-generated carriers in CIGS layers. CdS/CIGS p-n junction has been most widely employed and achieved the highest solar cell efficiencies. In general, CdS/CIGS p-n junctions are prepared using a chemical bath deposition (CBD) process in which CdS thin film is deposited by immersing CIGS thin film in the bath. As bath conditions in CBD process strongly affect properties of CdS thin film, it is very important to optimize conditions of bath. In this work, pH of immersion bath has been varied to study its effects on the properties of CdS/CIGS junctions as well as performance of CIGS thin film solar cells. It is confirmed that optimized pH condition can remarkably enhance both optical and electrical characteristics of the CdS/CIGS junctions. As a result, cell efficiency of 14.6% is achieved, which is one of the most efficient CIGS thin film solar cells.

Improvement in CIGS solar cell efficiency using a micro-prism array integrated with sub-wavelength structures

Lee, Soo Kyung,Jeong, Ho-Jung,Kim, Ye-Chan,Jang, Jae-Hyung Elsevier 2018 Solar energy materials and solar cells Vol.186 No.-

<P><B>Abstract</B></P> <P>A micro-prism array (MPA) integrated with subwavelength structures (SWSs) was employed to improve the efficiency of a CuIn<SUB>1-x</SUB>Ga<SUB>x</SUB>Se<SUB>2</SUB> (CIGS) solar cell by minimizing optical reflection losses caused by the metal grids. The MPA mounted on the CIGS solar cell refracted incident light normal to the grid into the nearby surface of the solar cell, thereby minimizing the optical reflection losses caused by the metal grids. Furthermore, to reduce reflection losses at the surface of the MPA, SWSs were formed on the MPA glass. This resulted in increased photovoltaic current, which enhanced the power conversion efficiency (PCE) of the solar cells. The final short circuit current density and the PCE of the CIGS solar cells with MPA glass integrated with SWSs were improved by 9.0% and 8.5%, respectively, compared with those of a CIGS solar cell without cover glass.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The micro-prism array (MPA) refracts light propagating toward the grids into the inter-grid regions, thereby minimizing the optical losses caused by the metal grids. </LI> <LI> The omnidirectional antireflective subwavelength structures (SWSs) were realized on the MPA to reduce the reflection losses at the angled surface of the MPA. </LI> <LI> By employing MPA glass integrated with SWSs, the power conversion efficiency of CIGS solar cell was improved by 8.5%. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

도시 생활구조물 활용을 위한 CIGS 태양전지 심미성 향상 제품디자인 개발융합연구

조재윤,장희수,정제윤,남원석,장중식 한국융합학회 2020 한국융합학회논문지 Vol.11 No.4

본 논문은 도시 생활구조물 활용을 위한 CIGS 태양전지 심미성 향상 제품디자인 개발융합연구로써, 기존 태양 전지 패널의 문제점을 파악하고 제품디자인의 심미성 요소를 바탕으로 설문조사와 FGD [전문가 집단 토론]를 통해 CIGS 태양전지 심미성 향상을 위한 전문적인 심미성 요소를 도출하였다. 도출된 심미성 요소 중 ‘환경 조화성’, ‘패턴 균형성’, ‘시대 보편성’ 이렇게 상위 3종을 콘셉트로 제품 디자인 프로세스를 진행하여 심미성 향상을 위한 CIGS 태양전 지 모듈 디자인과 어셈블리 디자인을 도출하였으며, 제품 시뮬레이션을 통해 아파트, 베란다와 창호, 스트릿퍼니처에 적용했다. 본 연구는 추후 실제 도시 생활구조물에 활용해 심미성과 CIGS태양전지의 기능을 적용하기에 적합하며, 향 후 연구방향은 다양한 패턴과 구조적 디자인개발에 관한 연구가 필요하다. This paper is a product design convergence study to improve the aesthetic quality of CIGS solar cells for utilizing urban living structures, identifying problems of existing solar cell panels and drawing expert aesthetic elements for improving CIGS solar cells through survey and [Group discussion of experts] based on aesthetic elements of product design. Out of the aesthetic elements derived, the top three models of the product design process were 'environmental harmonization', 'pattern balance', and 'period universality' to derive the design and assembly design of the CIGS solar cell module for improving aesthetic quality, and applied to apartments, veranda, windows, and streetcar through product simulation. This study is suitable for applying aesthetic and CIGS solar cell function later to actual urban living structure, and future research direction needs to be studied on various patterns and structural design development of design.

Improvement in the performance of CIGS solar cells by introducing GaN nanowires on the absorber layer

Sim, Jae-Kwan,Um, Dae-Young,Kim, Jong-Woong,Kim, Jin-Soo,Jeong, Kwang-Un,Lee, Cheul-Ro Elsevier 2019 JOURNAL OF ALLOYS AND COMPOUNDS Vol.779 No.-

<P><B>Abstract</B></P> <P>Cu(In, Ga) Se<SUB>2</SUB> (CIGS) thin-film solar cells are currently the fastest growing photovoltaic technology due to the higher performance ratio and lower energy payback time compared to the silicon, and good stability. Despite of these interesting properties, CIGS solar cells suffer from poor spectral response at short wavelengths particularly in the range of 300–400 nm. In the present work, we have introduced GaN nanowires in CIGS solar cells in order to improve the performance of photovoltaic device in the short wavelength region (300–400 nm). To evaluate the influence of GaN nanowires, the morphological, structural and electrical properties have been studied. These studies have shown the introduction of GaN nanowires not only improve the cell efficiency but also enhance the spectral response in the wavelength range 300–400 nm. The CIGS solar cells fabricated with GaN nanowires displayed power conversion efficiency of 10.15% with a fill factor of 65%, which are substantially higher than that of reference cell (without GaN nanowires).</P> <P><B>Highlights</B></P> <P> <UL> <LI> GaN nanowires have been incorporated in the CIGS solar cells. </LI> <LI> Introduction of GaN nanowires results in an improvement in the performance of CIGS solar cells. </LI> <LI> The CIGS solar cells with GaN nanowires displayed higher cell efficiency than a reference cell. </LI> <LI> Improved cell efficiency originated from boosted spectral response in the wavelength range 300–400 nm. </LI> </UL> </P>

CIGS 박막의 급속열처리 환경에 따른 CIGS 태양전지의 특성변화

김찬,이일수,김대환 한국물리학회 2012 새물리 Vol.62 No.3

Amorphous Cu(In,Ga)Se_2 (CIGS) films were deposited on molybdenum-coated soda-lime glass by using a co-evaporation method and were crystallized by using a rapid thermal process (RTP). Several different conditions for the RTP were used to investigate the effects of those conditions on the composition and the crystallization of the CIGS films. Less loss of selenium and more crystallization were observed in the CIGS film heat-treated at atmospheric pressure than in the film heat-treated in vacuum. In the film heat-treated with a glass cover, the loss of selenium was found to be even less, but the crystallization was not sufficient for use in CIGS solar cells. CIGS solar cells with a structure of AZO/ZnO/CdS/CIGS/Mo were fabricated with the CIGS films heat-treated under various conditions, and their characteristics were measured. The characteristics of the CIGS solar cells improved with the use of well-crystallized CIGS film. The energy conversion efficiency was largest for the CIGS solar cell with a CIGS film heat-treated at atmospheric pressure with no glass cover and with continuous argon flow. 몰리브덴이 증착되어 있는 유리기판 위에 비정질 Cu(In,Ga)Se_2 (CIGS)박막을 동시증발 방법으로 증착한 후 급속열처리 과정을 거쳐결정화시켰다. 이때 급속열처리 환경이 박막의 성분비와 결정화 정도에미치는 영향을 관찰하였다. 진공에서보다 상압에서의 열처리가 Se의소실은 줄이고, 결정 성장은 더 크게 만드는 것을 알 수 있었다. 그리고덮게 유리를 이용한 경우에는 Se의 소실은 줄일 수 있었지만 태양전지에사용할 정도로 결정성장이 충분히 되지 않는다는 것을 확인하였다. 이렇게 형성된 CIGS 박막들을 이용하여 AZO/ZnO/CdS/CIGS/Mo 구조의태양전지를 제작하고 특성을 확인하였다. CIGS 태양전지의 특성은 결정이크게 성장된 CIGS 박막을 이용한 태양전지에서 더 좋게 나왔으며, 덮게유리 없이 아르곤 가스가 흐르는 상압에서 열처리를 한 CIGS를 이용한태양전지 시료에서 가장 높은 에너지 변환효율인 4.0 %를 보여주었다.

공공시설물 심미성 향상을 위한 CIGS 태양전지 적용 방안

이샘,서지영,박수지,남원석,장중식 한국융합학회 2021 한국융합학회논문지 Vol.12 No.12

As environmental problems accompanied by industrialization have emerged worldwide, solar and wind energy have entered the stage of commercialization, especially in Korea. In addition, research on improving aesthetics using solar cells is being actively conducted. Examples include developing a transmissive solar cell and developing a solar cell with flexibility and color. Therefore, in line with the upward trend of solar cell development and solar cell-based public facility installation, we will present guidelines for designing public facilities using solar cells to improve aesthetics. First of all, components were derived to increase the suitability of solar cell application through literature surveys on solar cells and case studies on public facilities using solar cells. Next, through prior research on public facility guidelines, we established evaluation principles and drafted design guidelines. Based on this, a Delphi survey was conducted on a group of experts to verify its validity. Design guidelines for solar cells application measures to improve the final public design aesthetics were derived. The goal is to improve the public facilities using solar cells, through Accessibility and cognition, Usability, Shape and aesthetics, Sustainability and energy efficiency, Continuity with the urban landscape. And it is expected that this data will be used to improve the aesthetics of public design using solar cells in the future. 산업화와 동반한 환경문제가 세계적으로 대두되면서 특히 우리나라에서는 태양에너지와 풍력에너지가 실용화 단계에 접어들었다. 또한 태양전지를 활용한 심미성 향상에 대한 연구가 활발히 이루어지는 가운데 BIPV, CIGS등 투과가 가능한 태양전지 개발, 유연성과 색감을 가지고 있는 태양전지 개발이 그 예시이다. 이에 본 논문에서는 태양전지 개발 및 태양전지 기반의 공공시설물 설치 상승세에 발맞춰 심미성 향상을 위한 CIGS 태양전지를 활용한 공공시설물 디자인 가이드라인을 제시하고자 한다. 우선 태양전지에 관한 문헌조사와 태양전지를 활용한 공공시설물 사례조사를 통해 태양전지 적용의 적합성을 높이기 위한 구성요소를 도출했다. 그 다음 공공시설물 가이드라인 선행연구를 통해 평가원칙 정립과 디자인 가이드라인 초안을 작성했다. 이를 전문가 집단을 대상으로 3차례의 델파이조사를 실시하여 타당성을 검증했으며 최종적으로 공공디자인 심미성 향상을 위한 태양전지 적용 방안 디자인 가이드라인을 도출하였다. 향후 태양전지를 활용한 공공시설물의 접근성 및 인지성, 사용성, 형태 및 심미성, 지속가능성 및 에너지효율성, 도시경관과의 연속성 개선을 통한 심미성 향상의 기초자료로 활용되길 기대한다.

Efficiency enhancement of ultra-thin Cu(In,Ga)Se2 solar cells: optimizing the absorber bandgap profile by numerical device simulations

Xue Zheng,Weimin Li,Armin G. Aberle,Selvaraj Venkataraj 한국물리학회 2016 Current Applied Physics Vol.16 No.10

Thin-film chalcopyrite Cu(In1x,Gax)Se (CIGS) solar cells have recently achieved an efficiency of ~22% at the lab scale, making the technology more promising for commercial applications than most other thinfilm solar cells. Using numerical device simulations, this study provides approaches to enhance the efficiency of ultra-thin CIGS solar cells. Effects of various Ga grading profiles in the CIGS absorber and of surface bandgap modifications are simulated. Our simulation results reveal that, in ultra-thin CIGS solar cells, back grading is an effective and practical approach to increase the cell efficiency, while front grading is unfeasible due to unacceptable current and fill factor losses. The quality of the back surface is of particular importance in moderately graded cells, while interface and bulk defect properties dominate in extremely graded cells. By introducing an ordered vacancy compound (OVC) layer with a downwardshifted valence band at the CIGS surface, the interface recombination losses can be significantly suppressed due to the reduced hole concentration. The thickness of the OVC layer and the valence band offset (VBO) between the OVC and CIGS materials are critical parameters for the cell efficiency. The simulations reveal that an optimized CIGS cell with a 300 nm thick CIGS absorber, a back-graded absorber profile and a 70 nm thick OVC layer at the CIGS surface can reach a 1-Sun efficiency of over 12%.