S2281

Optically detected magnetic resonance experiments were carried out using a modified X-band spectrometer (Bruker E300) equipped with a continuous-flow helium cryostat (Oxford ESR 900) and a microwave cavity (Bruker ER4104OR, approximately 9.43 GHz) with optical access. Optical irradiation was performed with a 532 nm continuous-wave laser (Cobolt Samba CW 532 nm DPSSL) from one side-opening of the cavity. PL was detected with a silicon photodiode (Hamamatsu S2281) on the opposite opening, using a 561 nm long-pass filter to reject excitation light. The PL signal was amplified by a current/voltage amplifier (Femto DHPCA-100). For continuous-wave ODMR, PL was recorded by a lock-in detector (Ametek SR 7230) referenced by on–off modulation of microwaves with a frequency of 547 Hz. Microwaves were generated with a microwave signal generator (Anritsu MG3694C), amplified to 3 W (Microsemi) and guided into the cavity. For trODMR, PL was recorded by a digitizer card (GaGe Razor Express 1642 CompuScope) whereby a pulse blaster card (PulseBlasterESR-PRO) triggered the digitizer card and produced microwave pulses for a set length. Microwaves were generated with the same microwave signal generator as in continuous-wave ODMR, whereby they were amplified to 5 W by a travelling wave tube amplifier (Varian VZX 6981 K1ACDK) and guided into the cavity.

Measurements to estimate the ELQY were performed using a calibrated, large area Si-photodiode (Hamamatsu S2281). The organic solar cell (∼0.1 cm²) was positioned in the center and directly in front of the large area Si photodiode (1 cm²). A Keithley 2401 SMU was used to operate the solar cell as a LED, while another Keithley 2401 SMU was used to measure the photocurrent of the Si-photodiode. A detailed description of the used analysis procedure to determine the ELQY of the solar cells is provided elsewhere.^{9 (link)}