A cost-device efficiency balanced spiro based hole transport material for perovskite solar cells

Although spiro-MeOTAD 1 is a superior hole-transporting material (HTM) commonly employed in perovskite solar cells (PSC), its high cost is one of the major issues holding back commercialization, which has not been resolved to-date. In this article we introduce a new HTM comprising a cyclic spiro-backbone appended with four diphenylimidazole substituents, namely spiro-omethoxyimidazole, or spiro-OMeIm 2. When compared to the benchmark 1, introduction of the imidazole functionality into this versatile platform decreases the first oxidation potential from 0.6 V to 0.53 V, which approaches the energy of the HOMO of the perovskite light absorber. Studies on PSC devices fabricated from 2 reveal that the values of the short-circuit current (J(sc)) and open-circuit voltage (V-oc) are very similar to 1 and its power efficiency is 11.64 vs. 14.46% recorded for spiro-OMeTAD under the same conditions. Nevertheless, the commercial cost of synthesizing OMeIm is approximately 80% less than the synthetic precursors to the best spiro-OMeTAD derivatives reported to-date, which makes spiro-OMeIm less expensive to produce and therefore a very attractive HTM for the future development of low-cost PSCs.