CH3NH3PbI3 and HC(NH2)2PbI3 Powders Synthesized from Low‐Grade PbI2: Single Precursor for High‐Efficiency Perovskite Solar Cells

Abstract High‐efficiency perovskite solar cells are generally fabricated by using highly pure (>99.99 %) PbI 2 mixed with an organic iodide in polar aprotic solvents. However, the use of such an expensive chemical may impede progress toward large‐scale industrial applications. Here, we report on the synthesis of perovskite powders by using inexpensive low‐grade (99 %) PbI 2 and on the photovoltaic performance of perovskite solar cells prepared from a powder‐based single precursor. Pure APbI 3 [A=methylammonium (MA) or formamidinium (FA)] perovskite powders were synthesized by treating low‐grade PbI 2 with MAI or FAI in acetonitrile at ambient temperature. The structural phase purity was confirmed by X‐ray diffraction. The solar cell with a MAPbI 3 film prepared from the synthesized perovskite powder demonstrated a power conversion efficiency (PCE) of 17.14 %, which is higher than the PCE of MAPbI 3 films prepared by using both MAI and PbI 2 as precursors (PCE=13.09 % for 99 % pure PbI 2 and PCE=16.39 % for 99.9985 % pure PbI 2 ). The synthesized powder showed better absorption and photoluminescence, which were responsible for the better photovoltaic performance. For the FAPbI 3 powder, a solution with a yellow non‐perovskite δ‐FAPbI 3 powder synthesized at room temperature was found to lead to a black perovskite film, whereas a solution with the black perovskite α‐FAPbI 3 powder synthesized at 150 °C was not transformed into a black perovskite film. The α↔δ transition between the powder and film was assumed to correlate with the difference in the iodoplumbates in the powder‐dissolved solution. An average PCE of 17.21 % along with a smaller hysteresis [ΔPCE=PCE reverse −PCE forward )=1.53 %] was demonstrated from the perovskite solar cell prepared by using δ‐FAPbI 3 powder; this PCE is higher than the average PCE of 17.05 % with a larger hysteresis (ΔPCE=2.71 %) for a device based on a conventional precursor solution dissolving MAI with high‐purity PbI 2 . The smaller hysteresis was indicative of fewer defects in the resulting FAPbI 3 film prepared by using the δ‐FAPbI 3 powder.