Solar Cells: Understanding the Charge-Transfer State and Singlet Exciton Emission from Solution-Processed Small-Molecule Organic Solar Cells (Adv. Mater. 43/2014)

World‐record‐performing bulk‐heterojunction (BHJ) small molecule solar cells are realized by careful optimization of their solid‐state morphology. These BHJ films are transformed from an intimate mixture of the donor and acceptor phases to films with well‐defined donor crystallites. In addition to correlating with a high photovoltaic response, the donor crystallites also appear to be linked with the emergence of donor singlet electroluminescence at low applied biases, where only charge‐transfer‐state emission is expected. On page 7405, T.‐Q. Nguyen and co‐workers study three blends of high‐performing small‐molecule solar‐cell systems that show the same trend of emerging singlet emission upon an optimized photovoltaic response.