Enhanced Photoconversion Efficiency in CH$_{\mathrm{3}}$NH$_{\mathrm{3}}$PbI$_{\mathrm{3\thinspace }}$Solar Cells with Cadmium Incorporation

Non-radiative recombination is the primary energy loss in organic-inorganic metal halide perovskites solar cells, which significantly reduces the power conversion efficiency of the devices. To reduce the density of trap states that controls non-radiative recombination, it is important to prepare perovskite films consisting of large-sized grains with a high degree of crystallinity. Here, we show that the addition of small concentrations of Cd2$+$ in the methylammonium iodide precursor solution during the two-step sequential deposition can significantly improve the grain size and crystallinity of methylammonium lead iodide perovskite thin films. The grains are highly oriented in the \textless 110\textgreater direction compare to films produced by the standard two-step deposition, indicating a change in the growth mechanism. Time resolved photoluminescence measurements indicated a dramatic increase in the carrier lifetime which can be attributed to a reduction in the active trap density. Highly reproducible photovoltaic devices were obtained from the Cd-modified perovskites with a 13.8 {\%} device efficiency, while only 7.1 {\%} PCE was obtained from the standard two-step process.