Excitation of organic donor–acceptor systems with high-energy light can produce hot charge-transfer states that are delocalized across the heterojunction and readily dissociate. Two studies now reveal the dynamics of this process and pave the way towards unravelling the details of the molecular landscape that favours fast photocarrier generation.
The design and fabrication of solar cells in which at least one of the active components is a π-conjugated polymer has made tremendous progress over the past five years, and we are just beginning to see power conversion efficiencies reach the 10% milestone for realistic technological development1. Despite this progress, the mechanism of photocarrier generation in such devices has remained the subject of vivid debate, because the low dielectric constant of organic semiconductors generally aids electrostatic attraction and hinders the generation of free charges. Writing in Nature Materials, two sets of authors now address independently the dynamics of the earliest steps involved in photocarrier generation at organic donor/acceptor heterojunctions2