Precursor Formula Engineering Enabling High Quality Solution Processed C60 Films for Efficient and Stable Inverted Perovskite Solar Cellsprecursor Formula Engineering Enabling High Quality Solution Processed C60 Films for Efficient and Stable Inverted Perovskite Solar Cells

Solution processed fullerene (C60) films as the electron transport layers (ETLs) promise to substantially reduce the cost of the perovskite solar cells (PSCs). However, the self-aggregation nature of C60 when dissolved in a solvent with high solubility (e.g., o-dichlorobenzene, o-DCB) makes the efficiency of the resulting PSCs lower than 18%. In this paper, we proposed a new formula of the C60 precursor solutions, which can effectively inhibit the aggregation of C60 and advocates fast solvent drying. Homogeneous C60 films of high quality from the new formula solution (N-C60) can be readily fabricated at room temperatures, advocating the efficiency of the printed PSCs to over 17%. Attractively, the price of N-C60 is only 1/6 of its counterpart PCBM. Finally, a champion efficiency of over 20% for the PSCs was achieved which is comparable to that of the PSCs with PCBM as the ETLs. N-C60 based PSCs also show good stability, which sustain 85% of its initial efficiency as being exposed in air with a relative humidity (RH) of 50% for over 20 days. Our work helps to understand the film-formation dynamics of C60 by a solution method and cut the production cost of the PSCs to the bone