Effects of processing additives in non-fullerene organic bulk heterojunction solar cells with efficiency >11%

Here we investigate processing additive-dependent photovoltaic performance and charge recombination in organic bulk heterojunction (BHJ) solar cells based on a polymeric donor of PBDB-T blended with a non-fullerene acceptor m-ITIC. We find that PBDB-T:m-ITIC solar cells exhibit good compatibilities with the utilized additives (DIO, CN, DPE, and NMP) in optimal conditions, can have a high charge dissociation probability approaching 100% (with DIO), leading to ultimate efficiency >11%. Regardless of additives, we observe a dominant 1st order monomolecular recombination with insignificant bi-molecular recombination or space-charge effects in these solar cells. Despite of impressive power conversion efficiency (PCE), it is of surprise that Shockley-Read-Hall recombination is identified to play a role in device operation. Thus, it points to the necessity to mitigate the influences of traps to further boost the efficiency in non-fullerene based organic solar cells.