High-Performance Perovskite Solar Cells with a Non-doped Small Molecule Hole Transporting Layer

The use of solution-processed hole transporting layers (HTLs), without the need of added dopants, is important for the advancement of high-performance perovskite solar cells (PSCs). Here, a small molecule, N,N′-bis(naphthalen-1-yl)-N,N′-bis(phenyl)benzidine (NPB), is utilized as an efficient, dopant-free HTL in inverted PSCs to replace the commonly used poly(3,4-ethylenedioxythiophene):poly(styrenesulfonic acid) (PEDOT:PSS). A best power conversion efficiency (PCE) of 19.96% is realized when using NPB as the HTL, along with a short circuit current density (JSC) of 22.92 mA/cm2, an open circuit voltage (VOC) of 1.11 V, and a fill factor (FF) of 78.4%. This VOC is one of the highest obtained values in CH3NH3PbI3-based inverted PSCs and is comparable to devices with regular structure. The use of NPB as the HTL produced perovskite films with larger grain size and higher crystallinity than obtained with PEDOT:PSS. As a result of this improved perovskite film quality, recombination loss decreased dramatically, boosting JSC values. Furthermore, due to reduced recombination and better energy level alignment arising from the use of NPB, the VOC in the NPB-containing device increased considerably. In addition, NPB-based PSCs exhibited longer term stability as a result of the hydrophobicity of NPB.