In-depth understanding of photocurrent enhancement in solution-processed small-molecule:perylene diimide non-fullerene organic solar cells.

The experimental current is scaled by the generation, transportation and recombination loss of the mobile carriers. In this paper, we show that a change of small molecule/perylene diimide (PDI) weight ratio from 1:1 to 3:1 does not lead to different transportation or different recombination loss in the solar cell, while it results in different generation of the mobile carriers. With the increase of the donor/acceptor (D/A) ratio, the blend film has an enhanced absorption because the donor has a stronger light-harvesting ability than the PDI acceptor. With respect to the contribution from the enhancement of the absorption of the solar photons, our data demonstrate that the phase size of the acceptor (donor) domains is the key factor that determines the generation of the mobile carriers. We observe a good relationship between the average short-circuit current density ( JSC) and phase size of the acceptor domains. Through fine-tuning the D/A ratio, the best compatibility between the small molecule donor and the PDI acceptor is obtained at a mediate D/A ratio of 1.3:1, at which the absorbed solar photons are exploited efficiently, yielding an average power conversion efficiency of over 5.07 ± 0.10%. Compatibility and charge separation are modulated by varying donor weight ration in small molecule donor:perylene diimide based non-fullerene solar cells, which affords improved exploitation of the solar photons absorbed by the photoactive layer. The acceptor phase size is a key factor that scales the photocurrent. An efficiency of 5.1% is obtained from this non-fullerene small molecule system as a result of modulation of compatibility. [ABSTRACT FROM AUTHOR]