Design and synthesis of acceptor–donor–acceptor small molecule based on caffeine derivative for efficient and stable polymer solar cells

We designed and synthesized IDTBTCf (Indacenodithiophene-benzothiadiazolecaffeine) non-fullereneacceptor by using the caffeine derivative as the electron withdrawing end-group. It showed strongpolarization that is possible to improve stability by causing non-covalent interaction in active layer. When 2.5 wt% IDTBTCf was introduced as the third component in PTB7:PC71BM binary blend, the powerconversion efficiency (PCE) is more higher value of 8.7% than the reference (8.4%). As a result of stabilitymeasurement without encapsulation in a glove box for 172 h, a device with IDTBTCf (degradation rate ofefficiency, 8%) showed better stability than the reference one (degradation rate of efficiency, 15.5%).