Enhancing the power conversion efficiency of perovskite solar cells via the controlled growth of perovskite nanowires

The photovoltaic properties of perovskite solar cells (PSCs) are significantly influenced by the morphology of their constituent perovskite films. In this study, perovskite materials with two different morphologies, compact (c-perovskite) and nanowires (nw-perovskite), were prepared with a simple two-step spin coating solution process and their photovoltaic properties were investigated. We found that the presence of partially grown perovskite nanowires in the photoactive layer results in an excellent photovoltaic performance, i.e. a power conversion efficiency (PCE) of 18.7%. The shape and size of the perovskite nanowires are controlled by varying the concentration of N, N-dimethylformamide (DMF) in the methylammonium iodide (MAI) solution and keeping constant all other processing parameters such as the spin-coating speed and the annealing temperature. The optimal nw-perovskite film exhibits better light harvesting properties in the visible region, improved charge separation, and high charge carrier mobility. The mechanisms of charge carrier transfer in the two type of perovskites and their recombination dynamics were investigated by performing time-resolved photoluminescence (TRPL) and transient photovoltage (TPV) measurements respectively. Further, with an additional approach, the morphologies and solar cell performances of the c-perovskite and nw-perovskite films are improved by the addition of a fullerene derivative (PC60BM). These morphological advantages, together with the significant suppression of hysteresis effects, mean that the nw-perovskite: PC60BM photoactive film could be useful in the fabrication of high-performance PSCs.