Windows of opportunity for technology development appear and change as novel and revolutionary technologies are introduced, hence early detection of these changes in technological surroundings is a critical factor in technology forecasting.^[33] The strategic analysis of global technology foresight is in fact an integrated and comprehensive tool to be used by academic researchers and policy makers in decision making processes. It is envisaged to be a crucial approach in identifying strategic national demands and grasping the global trend of innovative technology.^[34] It enables organizations, ranging from the multinational level (e.g., the European Union) to the individual level (e.g., a research center), to build roadmaps depicting their strategies to discover rational ways to develop technology and innovation policies when facing social and economic development uncertainties.^[35,36] It further allows for the anticipation of technological ruptures, discontinuities, new perspectives, and opportunities in a given time horizon.

Daim et al. have however previously claimed that forecasting an emerging technology is daunting task as there is no historical data available, however in such cases the use of bibliometrics may provide useful data.^[37] Hence accordingly, in the present study the international trends in DSSC technology have been analyzed using bibliometric approach. In total, there were 10484 research items pertaining to DSSC research field in the ISI web database between 2007 and November 2017, with eleven document types. Specifically, there were 9489 research articles comprising 90.51% of the total production, followed by proceedings papers (379, 3.61%), meeting abstracts (298, 2.84%), and reviews (215, 2.05%). The other research items with less significant percentage were corrections (70), editorial materials (11), letters (7), news items (7), book chapters (5), retracted publications (2), and retraction (1). Since, the original research articles and reviews were frequently used document types and were also peer-reviewed. Therefore, both of them (9704 total publications with h-index = 187) were used for further analysis in the present bibliometric study.

The publications and citations trends related to DSSC research field within 2007 to November 2017 timeframe are depicted in Figs. 1(a) and 1(b), respectively. From Fig. 1(a), it may be observed that the annual global publications have increased significantly from 2007 to 2014. Specifically, the number of articles increased more than six times, i.e., 228 in 2007 to 1459 in 2014. The highest number of articles published in 2014 accounted for 15.03% of the total number of articles (9704) in the above time span. The general progression in DSSC research publications pertains to the growing importance of solar energy research under the pressures of reducing carbon emissions, meeting increasing electricity demand, and sustaining economic growth. Further from Fig. 1(b), it is observed that the annual citations of 9704 DSSC research documents also increased generally along the study period. Specifically, there were 272202 citations with an average of 28.05 citations per published article. The cumulative cited reference count increased nearly 190 times, from 205 to 38966, during these nearly eleven years of time span.

Fig. 1.

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	Fig. 1. The progression in annual (a) global research publications and (b) cumulative citations of DSSC publications along the study period (2007 to November 2017).

Interestingly, while characterizing the basic performance of scholarly outputs during the study period, it has been observed that the number of DSSC publications has decreased during 2014 to November 2017, as depicted in Fig. 1(a). The relative decrease in DSSC publications from 2014 to November 2017 may be an indication of the recent shift in global research interest towards developing a novel breed of highly efficient and stable hybrid organic–inorganic perovskite solar cells.^[38–40] The emerging perovskite solar cells technology exhibits promising characteristics such as superior light absorptivity, higher charge-carrier mobility, tunable bandgap, longer exciton diffusion length, and low exciton binding energy.^[33] By virtue of these enticing properties, the perovskite solar cells have undergone unprecedented development, resulting in a dramatic increase in their power conversion efficiency (PCE) exceeding 23% within past couple of years.^[41]

Based on these aforementioned results, a review of technology foresight activities in organic–inorganic hybrid perovskites solar cells may be the future research agenda. It is particularly attractive in terms of governmental practices and policy applications, which may provide some potential implications for technology foresight practices and in identifying directions for future research initiatives related to organic–inorganic hybrid perovskites solar cells.

Table 1 shows the top fifteen publications pertaining to DSSC research, listed in the order of times cited. Admittedly, the cumulative citation is not a direct measure of the impact or importance of a particular scholarly work, it does, however, provide a marker of its recognition within the scientific community.^[42] Also, the top-cited articles can also provide insights into how research fields have evolved.^[43] From Table 1, it can be clearly observed that in DSSC research field, the most cited paper in the past 11 years is the review article “Dye-sensitized solar cells” by A. Hagfeldt et al. Within the review article, the authors have overviewed DSSC research in a broad sense, i.e., operational principles of DSSC (energetics and kinetics), development of material components along with the specific experimental techniques to characterize DSSC. Further intrigued by the fact that the manufacturing, reliability, performance, and stability of a DSSC module are complicated, the authors have also reviewed DSSC modules design and their performance with specific focus on manufacturing processes and accelerated stability testing of modules.

Table 1.

Table 1.

Table 1. Fifteen most frequently cited articles in the field of DSSC research along the study period. . No. Title Authors Journal Year Times cited 1 Dye-sensitized solar cells Hagfeldt et al. Chemical Reviews Nov, 2010 4745 2 Transparent, conductive graphene electrodes for dye-sensitized solar cells Wang et al. Nano Letters Jan, 2008 2652 3 Dye-sensitized solar cells with 13% efficiency achieved through the molecular engineering of porphyrin sensitizers Mathew et al. Nature Chemistry Mar, 2014 1824 4 Metal-free organic dyes for dye-sensitized solar cells: From structure: Property relationships to design rules Mishra et al. Angewandte Chemie International edition 2009 1611 5 Enhanced charge-collection efficiencies and light scattering in dye-sensitized solar cells using oriented TiO2 nanotubes arrays Zhu et al. Nano Letters Jan, 2007 1608 6 Growth of oriented single-crystalline rutile TiO2 nanorods on transparent conducting substrates for dye-sensitized solar cells Liu et al. Journal of the American Chemical Society Mar, 2009 1408 7 Fabrication of thin film dye-sensitized solar cells with solar to electric power conversion efficiency over 10% Ito et al. Thin Solid Films May, 2008 1271 8 ZnO nanostructures for dye-sensitized solar cells Zhang et al. Advanced Materials Nov, 2009 1056 9 Enhance the optical absorptivity of nanocrystalline TiO2 film with high molar extinction coefficient ruthenium sensitizers for high performance dye-sensitized solar cells Gao et al. Journal of the American Chemical Society Aug, 2008 1031 10 Highly efficient light-harvesting ruthenium sensitizer for thin-film dye-sensitized solar cells Chen et al. ACS Nano Oct, 2009 836 11 The renaissance of dye-sensitized solar cells Hardin et al. Nature Photonics Mar, 2012 729 12 Characteristics of the iodide/triiodide redox mediator in dye-sensitized solar cells Boschloo et al. Accounts of Chemical Research Nov, 2009 705 13 Efficient dye-sensitized solar cells with an organic photosensitizer featuring orderly conjugated ethylenedioxythiophene and dithienosilole blocks Zeng et al. Chemistry of Materials Mar, 2010 694 14 Mesoporous anatase TiO2 beads with high surface areas and controllable pore sizes: a superior candidate for high-performance dye-sensitized solar cells Chen et al. Advanced Materials Jun, 2009 684 15 Large π-aromatic molecules as potential sensitizers for highly efficient dye-sensitized solar cells Imahori et al. Accounts of Chemical Research Nov 2009 653

Table 1. Fifteen most frequently cited articles in the field of DSSC research along the study period. .

From the data analysis, it has been found that 4397 articles were published by top 15 journals which account for about 45.3% of the total publications. Table 2 arranges the top 15 journals in order of decreasing DSSC articles published along the study period. These fifteen journals may be regarded as the important set of journals in the DSSC research field. Electrochimica Acta (England) has been identified as a core journal with 595 articles, which is about 6.13% of the total publications, followed by Journal of Physical Chemistry C (United States), which published 519 articles (∼ 5.35%) as shown in Table 2. It is also pertinent to mention that a total of 9582 publications (∼ 98.75%) were in the English language, whereas 92 (∼ 0.95%), 24 (∼ 0.24%), and 3 (∼ 0.031%) were in Chinese, Korean, and Japanese languages, respectively.

Table 2.

Table 2.

Table 2. Top fifteen productive journals in the field of DSSC research along the study period. . No. Source titles Impact factor (2017) Country Publications % of total publications 1 Electrochimica Acta 4.798 England 595 6.131 2 The Journal of Physical Chemistry C 4.536 United States 519 5.348 3 RSC Advances 3.108 England 465 4.792 4 Journal of Power Sources 6.395 Netherlands 423 4.359 5 Journal of Materials Chemistry A 8.867 England 348 3.586 6 ACS Applied Materials & Interfaces 7.504 United States 301 3.102 7 Physical Chemistry Chemical Physics 4.123 England 244 2.514 8 Journal of Nanoscience and Nanotechnology 1.483 United States 220 2.267 9 Dyes and Pigments 3.473 England 215 2.216 10 Journal of Materials Chemistry A 8.867 England 211 2.174 11 Chemical Communications 6.319 England 201 2.071 12 Journal of Photochemistry and Photobiology A 2.625 Switzerland 180 1.855 13 Solar Energy 4.018 United States 167 1.721 14 Solar Energy Materials and Solar Cells 4.784 Netherlands 161 1.659 15 Energy & Environmental Science 29.518 United Kingdom 147 1.515

Table 2. Top fifteen productive journals in the field of DSSC research along the study period. .

The top 15 authors acknowledged for making their potential contributions to the DSSC research field are listed in Table 3, along with their respective publication numbers, h-indices, total citations, and average citation per article. It may be observed that the top 15 authors tabulated below account for 20.5% of the analyzed publications (9704) and 47.9% of the total number of citations (272202) during the time span of 2007 to November 2017. Grätzel M is the most productive author with 262 publications, followed by Kim J H and Ho K C (each with 178 and 169 publications). It is well-understood that the academic productivity of the author is measured by the number of publications. However, the influence of research publication is evaluated by the number of citations.^[44] Presently, the majority of citation databases are using h-index as a bibliometric indicator to assess significance and broad impact of a scientist’s cumulative research contributions.^[45] The h-index indicates the number of articles with citations that are greater than or equal to this number “h”. Interestingly, during the past eleven years, Grätzel M has been found to be the most influential researcher as well from h-index perspective. Grätzel M ranks first in the influential global DSSC researchers list with the highest h-index and cumulative citations of 89 and 27921, respectively.

Table 3.

Table 3.

Table 3. Top fifteen most productive authors in the field of DSSC research along the study period. . No Author Total publications h-index Sum of times cited Average citation per article 1 Grätzel M 262 89 27920 106.56 2 Kim JH 178 29 3020 16.97 3 Ho K C 169 40 5277 31.22 4 Hagfeldt A 161 58 16419 101.98 5 Wu J H 135 39 4792 35.5 6 Nazeeruddin M K 134 55 13204 98.54 7 Zakeeruddin S M 125 57 14001 112.01 8 Zhang J 124 33 5144 41.48 9 Dai S Y 120 27 2122 17.6 10 Sun L C 102 40 10653 104.44 11 Wang P 102 42 8895 87.21 12 Boschloo G 101 38 10619 105.14 13 Wang H 100 30 3155 31.55 14 Han L Y 92 29 2944 32 15 Tang Q W 90 26 2278 25.31

Table 3. Top fifteen most productive authors in the field of DSSC research along the study period. .

Among the top most productive institutes in DSSC, eight institutes are from China, four from South Korea, and one institute each from Switzerland, Sweden, and Singapore. The Chinese Academy of Sciences (China, Asia) has the maximum contribution with 591 articles (h-index = 70) in the total volume of publications, followed by the Ecole Polytechnique Federale De Lausanne (EPFL) in Switzerland (318 articles, 119 h-index). The higher output of DSSC research in Chinese Academy of Science is not surprising since in the past China’s total expenditure on research and development (R&D) has been increasing by about 20% per year.^[46] However, it is also pertinent to mention here that the Chinese Academy of Sciences is an integrated research center consisting of many relatively independent institutes distributed across China, thus their publication productivity is particularly notable. Interestingly, National University of Singapore (NUS) is the most productive university in the South-East Asian region. NUS ranked 14th in the global most productive institute’s list with 115 DSSC related publications and 41 h-index. This performance of NUS should be seen in the light of the substantial scientific R&D funding in the Singapore federal budget.

Table 4 shows the top 14 countries, ranked according to the total number of DSSC related publications along the study period (also shown in Fig. 2). The list of most productive countries includes six Asian countries, six European countries, America, and Australia. The People’s Republic of China is the most productive country with ∼ 34.97% of the total output, followed by South Korea whose share is ∼ 15.04% of the total output. Five of the seven advanced economies of the world (G7), the USA, Japan, Italy, Germany, UK, and France, were in the top 14 productive countries list, while France and Canada took the 18th and 23rd place, respectively. The domination of the Asian countries in general in DSSC research publications reflects the high scientific investment and academic level of these countries. Moreover, since the Asian countries in general are in the process of industrialization and electricity is indispensable for their rapid industrial growth.^[47,48] Therefore, the developments of eco-benign electric power industry, photovoltaic, energy saving, and greenhouse gases emission reduction are themes of paramount importance in the Asian countries.

Fig. 2.

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	Fig. 2. Regional contribution (of top 14 productive countries) in the field of DSSC research along the study period.

Table 4.

Table 4.

Table 4. Top fourteen productive countries in the field of DSSC research along the study period. . No. Country Region Publications % of total publications 1 China East Asia 4328 34.975 2 South Korea East Asia 1460 15.045 3 USA North America 840 8.656 4 Japan East Asia 799 8.234 5 India South and South East Asia 794 8.182 6 Switzerland Europe 375 3.864 7 Sweden Europe 305 3.143 8 Italy Europe 300 3.092 9 Iran Central Asia 267 2.751 10 Australia Australia 260 2.679 11 Germany Europe 242 2.494 12 England Europe 228 2.35 13 Singapore South and Southeast Asia 228 2.35 14 Spain Europe 196 2.02

Table 4. Top fourteen productive countries in the field of DSSC research along the study period. .

From the perspective of socio-economic development, it is well known that science and technology policies have integrated with policies in other fields by means of their relation to economy and to the transformation of societies. Pelaiz A L has previously claimed that the technology plays an indispensable role in the evolution of society and of current economies, to the point that it has now become a central element of economic evolution.^[49] For global development and prosperity, international academic cooperation is of prime importance since the developing countries with backward technologies can learn advanced experiences from the developed countries. Consequently, through synergistic collaborative efforts, the researchers may enhance their understandings, share ideas, and seek innovative solutions to research problems. Based on the statistics for various countries, the People’s Republic of China has played a pivotal role in the collaboration network of the top 14 productive countries. It had research collaborations with nine top productive countries. Among them, the research cooperation between China and US is particularly notable, rising to the first place in intensity. Spain’s relatively limited amount of DSSC related research publications accounts for its peripheral location in this network diagram, and the thin lines connecting it to other countries.