Unraveling optimal interfacial conditions for highly efficient and reproducible organic photovoltaics under low light levels

The insertion of interfacial layers between the photoactive layer and electrodes is effective for improving the power conversion efficiency (PCE) of organic photovoltaics (OPVs). Further understanding on effects of the interlayers is needed to optimize OPV performance in low light applications, as the operating mechanism of OPVs varies depending on the light intensity. Here, the critical roles of the electron transport layer (ETL) on the performance of OPVs are demonstrated in different irradiation environments involving low-intensity lighting. ZnO ETL was found to deliver better performance and reproducibility compared with a conjugated polyelectrolyte ETL regardless of the irradiation conditions, showing high PCEs exceeding 18% under low light conditions such as a 500 lx light-emitting diode. In addition to the great charge selectivity and electronic properties, the uniform surface coverage of the bottom indium tin oxide electrode was a key factor in preventing shunt path formation and consequently reducing recombination and leakage current, which mainly determine the low light performance of OPVs. This study provides important design considerations for interfacial contact materials to achieve high-performance and reproducible OPVs that operate unconditionally over a wide range of light intensities for various applications.