Engineering Charge Transport and Defect Passivation via CdSe Nanoplatelet Doping in Organic Bulk-Heterojunction Solar Cells

Non-radiative carrier loss originating from material defects together with slow charge migration act as two major limiting factors heavily suppressing the power output performance of organic bulk-heterojunction (BHJ) photovoltaic devices (OSCs). Herein, two-dimensional (2D) CdSe nanoplatelets (NPLs) are introduced into conventional P3HT:PCBM and high-efficiency PBDB-T:PCBM photoactive films as multi-purpose doping additives, aiming to finely tune film microstructures, refine interfacial energy level matching, accelerate carrier migration, and eliminate native trap sites inside the active layer. Statistical measurement data verify that 3 mg CdSe NPLs as the ideal doping dosage can realize concurrent performance upgrades for the two distinct OSC architectures investigated here. As for devices built on P3HT:PCBM blend films, the component modified with optimized CdSe NPL additives delivers boosted charge mobility rising from 0.87 × 10−5 cm2/V·s up to 2.58 × 10−5 cm2/V·s. Meanwhile, trap site concentration drops markedly from 7.41 × 1015 cm−3 to 4.33 × 1015 cm−3, which lifts the device power conversion efficiency (PCE) from 2.77% to 3.15%. Even more noticeable improvements are observed in PBDB-T:PCBM photovoltaic units; the refined doping recipe raises carrier mobility from 5.42 × 10−4 cm2/V·s to 8.69 × 10−4 cm2/V·s and cuts trap density down from 7.13 × 1016 cm−3 to 3.15 × 1016 cm−3, thus bringing about a substantial PCE boost ranging from 6.52% to 9.14%. The present study confirms the bifunctional advantages possessed by 2D CdSe NPLs, which can adjust BHJ microphase separation and electronic characteristics simultaneously. This research offers a simple and broadly applicable route to fabricate organic photovoltaic cells with superior efficiency.