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

pi-Extended donor-acceptor conjugated copolymers for use as hole transporting materials in perovskite solar cells

We introduced 3-octylthiophene (OT) or 3-octylthieno [3,2-b]thiophene (OTT) as pi-bridges into PBT (poly(1-(4,8-bis(5- (2-ethylhexyl)selenophen-2-yl)benzo[1,2-b:4,5-b']dithiophen-2-yl)-5-(2-butyloctyl)-4H-thieno[3,4-c] pyrrole-4,6(5H)-dione), which is based on benzodithiophene and thienopyrmlodione units, in order to prepare thiophene-based pi-bridging donor-acceptor conjugated copolymers for use as hole-transport layers in pemvskite solar cells (PeSCs). The resulting polymers exhibit strengthened intermolecular pi-pi stacking and increased crystallinity (dominant face-on orientation), which facilitates vertical charge transport and hole mobility. Moreover, the highest occupied molecular orbital level of PBT-OTT is similar to the valence band of the perovskite material. As a result, efficient hole extraction occurs with reduced charge carrier recombination in PBT-OTT-based PeSCs. Therefore, the introduction of pi-bridges to extend the pi-conjugation length of conjugated polymers is a promising strategy for the development of efficient hole-transporting materials for use in PeSCs.11Nsciescopu