We studied and compared the reported characteristics of 22 different bulk heterojunction organic solar cells fabricated and characterized by different research institutes. We only considered bulk heterojunction solar cells where both the acceptor (the n-type) and the donor (the p-type) are organic. All cells were characterized under illumination with the standard A.M. 1.5 spectrum and an intensity of 100 mW/cm2. The material properties (the highest occupied (HOMO) and lowest unoccupied molecular orbital (LUMO) of donor and acceptor) and the device characteristics (the open circuit voltage Voc, the short circuit current density Jsc, the fill factor FF and the efficiency) are compared and related to each other. One finding is that not the Voc, but the Jsc is the limiting factor for obtaining a high efficiency with the current state of technology. Also an empirical threshold of 0.2 eV is found between the LUMO's of the donor and acceptor, necessary for exciton dissociation. There has long been a debate about the origin of the Voc. In recent literature, it is proposed that the Voc is not related with the work function difference of the contacts, but with the energy difference between the LUMO of the acceptor, and the HOMO of the donor (called `the interface bandgap'). A relation between the Voc and the energy levels of donor and acceptor is searched from our empirical study.

By action of the Executive Committee of IAU, the report for 1970 is restricted to half the length of the 1967 draft report; the bibliography and the abstracting of work already published are essentially eliminated. The report is no longer to serve primarily as a review of accomplishments between General Assemblies but rather as a report of work in progress. These changes were adopted by the Executive Committee in order to reduce the cost of publishing the reports.

Several commission members have voiced the opinion that the extensive bibliographies in past reports have been the most valuable contributions of the reports and they have objected to the elimination of the bibliography. Also, material from some observatories and from some national groups that have been submitted for inclusion in this draft report have contained only abstracts of work already published. The rules adopted by the Executive Committee do not permit the report to abstract published works except in evaluating general progress in solar astronomy. We express our regret to these commission members and to these institutions that we have not been able to include the abstracts and bibliography in the present report.

Selon les instructions reçues de la part du Secrétaire Général de l’UAI, l’esprit général du présent “Draft Report” de la Commission 17 “La Lune” ne doit plus représenter, comme par le passé, un résumé des travaux effectués dans la discipline au cours des trois dernières années. Son rôle sera de donner un aperçu général sur les aspects et les tendances des recherches sur la Lune, la contribution présente et future de la Commission 17 du l’UAI dans son développement, ainsi que les coopérations dont elle est l’objet ou devrait l’être dans l’avenir.

During the 13th IAU General Assembly in Prague it was decided that each nation adhering to the IAU should be represented in Commission 46 by one member interested in the teaching of Astronomy. Six nations were already represented by the members of the Organizing Committee. For all other nations the Commission President contacted the head of the National Delegations to the IAU with the request to designate one IAU member of the particular country as member of Commission 46. With only a few exceptions every IAU member nation designated a representative in this Commission which now contains representatives of 33 nations. It is hoped that the missing nations in our Commission will also soon be represented by an IAU member active in the promotion of Astronomy education. Each member is responsible to (a) promote the teaching of Astronomy in his own country, (b) to keep in touch with the Astronomy teachers of his country, and (c) to communicate to the Commission President any programs and developments, problems and needs concerned with Astronomy education in his country. It is also hoped that institutions in countries not yet adhering to the IAU but which might wish to start some Astronomy teaching, could contact the Commission and, in some specific cases, could designate a Consulting Member to the Commission.

Since the last report in 1960, a total number of 25 grants has been made to 27 astronomers. This is about the average number of the last ten years. Considering the increasing importance of astronomy, one might have expected a quicker development of international travel and exchange. All efforts should be made to stimulate the mobility of astronomers and to make effective use of the wonderful possibilities now available. It should be stressed that the IAU grants can be awarded for a stay of any duration of time, and that practically all applications are answered positively and quickly.

During this part of the Symposium, so carefully prepared by Messrs. Denisse and Pawsey, a great amount of new data has been presented, almost all obtained since the last international meeting on these subjects only one year ago. It is clear that this is a part of astronomy that develops impetuously. Hypothetical theories have been definitely confirmed by direct observation; on the other hand, new facts have been disclosed, increasing the complication of the phenomena; but we have reason to hope that we are in a transitory stage and that the complications will gradually be explained on clear and simple principles. It is of course impossible to mention in this summary the contents of all communications; only the more essential results will be reviewed.

The analysis of the Sun by spectroscopic methods refers to an exceedingly thin layer, just above the photosphere, which has a thickness of only a few hundreds of kilometers. The deeper layers are inaccessible to our investigations, because there the matter becomes too opaque. The higher layers of the chromosphere and the corona again are less well known, because they are too transparent, so that deviations from thermodynamic equilibrium conditions may occur. So it is understandable that just the layer where the equilibrium is nearly established must be the only layer which can be fully investigated. Probably this is the best analysed sample of the universe. Whether the composition here found is really representative for the Sun as a whole depends on the importance of the convection, which tends to stir the gases into one homogeneous mixture.

By publishing at each meeting a report on the progress of astronomical spectrophotometry, our Commission has done in the past work which has been appreciated. Such a report may be expected to be of special usefulness in the present circumstances, after the disruption of normal communications for so many years. For this purpose, an attempt has been made to give a list of the most important publications, as a bibliographical appendix to this report. The titles are quoted in abridged form. My thanks are due to many members of the Commission, who contributed materially to this list and helped me with important information. I apologize for omissions, nearly inevitable in this post-war period. In future some restriction of the field of our activity ought to be considered; spectrophotometry is nowadays so general an astrophysical method, that it is nearly impossible to give a more or less complete survey of its applications to all different fields of our science. This report was finished on January 1, 1948. A few recent publications have been included in the bibliographical list.

Since the date of the 1935 Paris meeting two total eclipses have been successfully observed. Throughout the long path crossing Siberia and Japan the weather on June 19, 1936 on the whole about lived up to predictions. On account of widely scattered clouds neighbouring expeditions had quite different luck with the weather. In contrast, the June 8, 1937 eclipse was seen throughout the whole track under universally clear skies, which is all the more surprising for the reason that eclipse expeditions to the tropics usually fare badly with the weather. Stewart and Stokley in a ship at sea were able to observe the eclipse with a measured duration of 7 min. 6 sec., the longest period of totality in 1200 years.