A dopant-free organic hole transport material for efficient planar heterojunction perovskite solar cells

Abstract

We demonstrate efficient planar perovskite solar cells using a dopant-free donor–acceptor (D–A) conjugated small molecule as a hole transport material. The photovoltaic cell reaches a power conversion efficiency (PCE) of 14.9%, which is comparable to or even better than that of the devices using the traditional doped 2,2′,7,7′-tetrakis(N,N′-di-p-methoxyphenylamine)-9,9′-spirobifluorene (spiro-OMeTAD) hole transport material under equivalent conditions. We ascribe the high performance to the excellent charge transporting properties of the D–A conjugated small molecule. Time-resolved photoluminescence (PL), transient photocurrent response, and impedance spectroscopy characterization indicate that this D–A conjugated small molecule plays a key role in hole collection and extraction in perovskite based photovoltaic devices. The dopant-free D–A small molecule hole transport material used here not only improves the efficiency, but also facilitates the fabrication process and thus potentially reduces the fabrication cost of perovskite solar cells.