Highly Efficient Integrated Perovskite Solar Cells Containing a Small Molecule-PC₇₀BM Bulk Heterojunction Layer with an Extended Photovoltaic Response Up to 900 nm

We demonstrate a high efficiency perovskite solar cell (PSC) integrated with a bulk heterojunction layer, based on acceptor–donor–acceptor (A–D–A) type hole transport material (HTM) and PC 70 BM composite, yielding improved photoresponse. Two A–D–A-structured hole transporting materials termed M3 and M4 were designed and synthesized. Applied as HTMs in PSCs, power conversion efficiencies (PCEs) of 14.8% and 12.3% were obtained with M3 and M4, respectively. The HTMs M3 and M4 show competitive absorption, but do not contribute to photocurrent, resulting in low current density. This issue was solved by mixing the HTMs with PC 70 BM to form a bulk heterojunction (BHJ) layer and integrating this layer into the PSC as hole transport layer (HTL). Through careful interface optimization, the (FAPbI 3 ) 0.85 (MAPbBr 3 ) 0.15 /HTM:PC 70 BM integrated devices showed improved efficiencies of 16.2% and 15.0%, respectively. More importantly, the incident-photon-to-current conversion efficiency (IPCE) spectrum shows that the photoresponse is extended to 900 nm by integrating the M4:PC 70 BM based BHJ and (FAPbI 3 ) 0.85 (MAPbBr 3 ) 0.15 layers.