Reduction in the temperature coefficient of photovoltaic efficiency in all-polymer solar cells using molecular order

Controlling the phase morphology of photoactive layers toward satisfactory charge transport with reduced energetic disorder is the key to obtaining targeted efficiencies in organic solar cells (OSCs). On the basis of an all-polymer model system, i.e., PM6/PYF-T-o, we investigated the effects of phase morphology on temperature-dependent charge carrier transport and photovoltaic behavior in all-polymer solar cells prepared through a layer-by-layer (LBL) process. The combined in-situ spectroscopic and morphological analyses reveal that the formation of a fibril structure during the self-assembly of donor molecules and the favorable pure phase of a polymeric acceptor component could promote charge transport. Such morphological features reduce the thermal activation energy (Ea) for the carriers. The LBL-processed PM6/PYF-T-o solar cells exhibit a surprisingly small temperature coefficient of power conversion efficiency (PCE), i.e., upon cooling the device to 215 K, the PCE remains at 94.0% of the value at ambient room temperature (RT = 298 K) (PCE of 15.65% at 215 K and 16.70% at RT). This study offers an attractive approach for mediating carrier transport and photovoltaic performance in OSCs toward applications in a temperature-variable environment.