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Since January 1993, ‘Progress in Photovoltaics’ has published six monthly listings of the highest confirmed efficiencies for a range of photovoltaic cell and module technologies 1–3. By providing guidelines for the inclusion of results into these tables, this not only provides an authoritative summary of the current state of the art but also encourages researchers to seek independent confirmation of results and to report results on a standardised basis. In a recent version of these tables (Version 33) 2, results were updated to the new internationally accepted reference spectrum (IEC 60904–3, Ed. 2, 2008), where this was possible.
The most important criterion for inclusion of results into the tables is that they must have been measured by a recognised test centre listed elsewhere 1. A distinction is made between three different eligible areas: total area; aperture area and designated illumination area 1. ‘Active area’ efficiencies are not included. There are also certain minimum values of the area sought for the different device types (above 0.05 cm2 for a concentrator cell, 1 cm2 for a one-sun cell and 800 cm2 for a module) 1.
Results are reported for cells and modules made from different semiconductors and for subcategories within each semiconductor grouping (e.g. crystalline, polycrystalline and thin film). From Version 36 onwards, spectral response information has been included when available in the form of a plot of the external quantum efficiency (EQE) versus wavelength, normalized to the peak measured value.
Highest confirmed “one-sun” cell and module results are reported in Tables I and II. Any changes in the tables from those previously published 3 are set in bold type. In most cases, a literature reference is provided that describes either the result reported or a similar result. Table I summarises the best measurements for cells and submodules, while Table II shows the best results for modules. Table III contains what might be described as ‘notable exceptions’. While not conforming to the requirements to be recognized as a class record, the cells and modules in this Table have notable characteristics that will be of interest to sections of the photovoltaic community with entries based on their significance and timeliness.
Table I. Confirmed terrestrial cell and submodule efficiencies measured under the global AM1.5 spectrum (1000 W/m2) at 25°C (IEC 60904–3: 2008, ASTM G-173–03 global).
To ensure discrimination, Table III is limited to nominally 10 entries with the present authors having voted for their preferences for inclusion. Readers who have suggestions of results for inclusion into this table are welcome to contact any of the authors with full details. Suggestions conforming to the guidelines will be included on the voting list for a future issue.
Table IV shows the best results for concentrator cells and concentrator modules (a smaller number of ‘notable exceptions’ for concentrator cells and modules additionally is included in Table IV).
Table IV. Terrestrial concentrator cell and module efficiencies measured under the ASTM G-173–03 direct beam AM1.5 spectrum at a cell temperature of 25°C.
Fourteen new results are reported in the present version of these Tables.
The first new result in Table I is an outright record for solar conversion by any single-junction photovoltaic device. An efficiency of 27.6% has been measured at the National Renewable Energy Laboratory (NREL) for a 1 cm2 thin-film GaAs device fabricated by Alta Devices, Inc.. Alta Devices is a Santa Clara based “start-up” seeking to develop low-cost, 30% efficient solar modules 4.
The second new result in Table I is an efficiency improvement to 19.6% for a 1 cm2 single-junction copper–indium–gallium–selenide (CIGS) cell fabricated by and measured at NREL 5. Although CIGS efficiency of 20% and higher has been reported previously by two groups (see Table III), this has been for cells appreciably less than 1 cm2 in area, the minimum considered reasonable for efficiency comparisons in these Tables and for milestones in most of the international programs.
A third new result in Table I is 12.5% efficiency for an eight cell 35 cm2 CdTe submodule fabricated by Advanced Solar Power (ASP) Hangzhou, also measured by NREL.
A fourth new result in Table I is for a dye sensitized submodule with efficiency of 9.9% reported for a 17 cm2 submodule fabricated by Sony 6 and measured by the Japanese National Institute of Advanced Industrial Science and Technology (AIST). This is quite close to the record of 10.4% efficiency for the best individual dye sensitised cell yet confirmed (of more that 1 cm2 area).
Another outstanding new result is the measurement of 8.3% efficiency at NREL for a 1cm2 organic cell fabricated by Konarka 7, representing a massive improvement over the company's previous 5.15% record entry. An intermediate result of 6.5% was measured in July 2010.
Another new result in Table I is for a double-junction amorphous/microcrystalline silicon cell with stabilized efficiency of 11.9% reported for a 1.2 cm2 cell fabricated by Oerlikon and Corning 8 and again measured by NREL, after stabilization.
The final new result in Table I is for a double-junction organic solar cell with 8.3% efficiency measured for a 1.1 cm2 cell fabricated by Heliatek 9 and measured by the Fraunhofer Institute for Solar Energy Systems (FhG-ISE). This represents rapid progress from the 6.1% result from Heliatek measured in June last year and reported in the previous version of these Tables. An intermediate result of 7.7% was measured in March 2010.
Following a similarly vigorous burst of activity in the multicrystalline silicon module area reported in the two previous versions of these Tables, where four groups exceeded the previous record for module efficiency over the two reporting periods, a fifth group has done even better. In Table II, a new efficiency record of 17.55% is reported for a large (1.5 m2 aperture area) module fabricated by Schott Solar 10 and measured by the European Solar Test Installation, Ispra (ESTI).
Also reported in Table II is a record result for a thin-film module, with a large improvement to 15.7% reported for a 1 m2 CIGS module fabricated by Miasole 11 and measured by NREL.
The first new result in Table III relates to an efficiency increase to 24.2% for a large 155 cm2 silicon cell fabricated on an n-type Czochralski grown wafer, with the cell fabricated by SunPower 12 and also measured by NREL.
Another new result in Table III is the further improvement of a small area (0.5 cm2) CIGS cell fabricated by Zentrum für Sonnenenergie- und Wasserstoff- Forschung (ZSW), Stuttgart 13 to 20.3% efficiency as measured by FhG-ISE. This cell is smaller than the 1 cm2 size required for classification as an outright record, as previously discussed.
The final new result in Table III is for a luminescent concentrating submodule using high performance GaAs cells placed along the edge of a luminescent plate to convert the collected luminescent radiation. An efficiency of 7.1% was confirmed for a 25 cm2 test device fabricated by ECN, Netherlands 14 and measured by ESTI.
Two more new results are reported in Table IV for more conventional concentrator cells and systems. The first is a new efficiency record for any photovoltaic cell with 42.3% efficiency measured by NREL at 406 suns concentration (irradiance) for a 1 cm2 cell fabricated by the Spire Corporation 15. A new approach was used whereby a low bandgap InGaAs cell was grown on one side of a GaAs wafer, with the wafer then flipped over and an intermediate bandgap GaAs followed by a high bandgap InGaP cell grown on the other side.
The final new result represents a new record for the conversion of sunlight to electricity by any means. An efficiency of 38.5% was measured by NREL for a very small area (0.2 cm2) spectral-splitting submodule at about 20 suns concentration as the result of a multi-institutional effort headed by DuPont 16. This complete lens/cell assembly uses a dichroic reflector to steer light to two different two-cell stacks, one on a GaAs substrate and one on an InP substrate.
The external quantum efficiencies (EQE) normalized to the peak EQE values for the new organic cell results of Table I are shown in Figure 1(a) as well as the response for the GaAs cell and CdTe and dye-sensitised submodules of Table I. Also shown is the decomposition into the top and bottom cell response for the 8.3% Heliatek tandem cell of Table I. Interestingly, both cells in the stack have largely overlapping spectral response range, although complementary in some aspects.
Figure 1(b) shows the normalized EQE of the new CIGS and silicon results in the present issue of these tables. Quite striking is the almost identical responses of the NREL and ZSW CIGS cells with the higher current from the ZSW cell attributed to a slightly lower bandgap edge. The normalized responses of both cells in the Oerliken/Corning micromorph tandem cell are also shown.
Figure 1(c) shows the absolute EQE for the different cells contributing to the new concentrator cell and submodule results of Table IV. The much narrower response bandwidth of the bottom InGaAs cell in the 42.3% Spire monolithic stack compared to the response of the bottom Ge in the 41.6% Spectrolab device 3 reflects a higher bandgap. This gives a higher voltage output that contributes to the improved performance. The EQE for the 38.5% submodule differs slightly from results reported elsewhere 16 due to incorporation of the effect of the dichroic reflector used in this system. Each of the four cells in this system is contacted separately, removing the need for current matching.
While the information provided in the tables is provided in good faith, the authors, editors and publishers cannot accept direct responsibility for any errors or omissions.