Effective Hole Transfer from CH(NH2)2PbI3 Perovskite Quantum Dots to Conjugated Polymers: A Bridge for Carrier Extraction by the Organic Hole-Transporting Layer

Forperovskite quantum dot (PQD)-based solar cells, insertion ofa proper polymer/PQD bulk heterojunction (BHJ) connecting layer betweenPQDs and an organic hole-transporting layer (HTL) may improve thepower conversion efficiency (PCE). However, it is unknown whetherthe hole transfer from PQDs to the polymer plays an important rolefor the carrier extraction to circumvent the obstacle of direct holetransfer from PQDs to the HTL. In this work, we have used ultrafasttransient absorption spectroscopy (TAs) to investigate the chargetransfer in polymer/PQD BHJ films composed of FAPbI(3) (FA= CH(NH2)(2)) QDs and conjugated polymers (PBDB-T,PTB7, P3HT). The TA signals originated from PQDs decay much fasterin the PBDB-T/PQD BHJ film compared to the pure PQD film, and a characteristicphotoinduced bleaching signal of PBDB-T is emergent after the selectiveexcitation of FAPbI(3) QDs, which prove a substantial holetransfer from PQDs to PBDB-T. The hole transfer efficiency is calculatedto be 68.4%. In contrast, PTB7 and P3HT have negligible influenceon the TA signals of PQDs under selective excitation, indicating ineffectivehole transfer in these two BHJ films. The FAPbI(3) QD solarcells employing the PBDB-T/PQD BHJ as the active layer possess enhancedPCE compared to that using the pure PQD layer, whereas the decreasedPCE is obtained for devices with the BHJ of inefficient hole transfer.Our results provide insights that adding an optimal amount of conjugatedpolymer with an effective hole transfer from the PQDs is importantto facilitate overall charge carrier extraction in the PQD-based solarcells.