Solution-processed thin film solar cells based on colloidal quantum dot (CQD) and organic bulk heterojunction (BHJ) absorbers are compatible with low-cost, large-area manufacturing processes amenable to efficient, lightweight modules. In recent years, both CQD and organic photovoltaic devices have seen significant efficiency improvements, with single-junction devices reaching power conversion efficiencies (PCE) of over 12%. Yet, the progress in both fields has been seen primarily in laboratory scale champion devices prepared almost exclusively using spin-coating and employ halogenated additives (organics) or tedious ligand exchange schemes (CQDs). Surface traps in CQDs have also, indirectly, impeded scalable and industry-compatible fabrication of these solar cells as some of the CQD preparation steps need to be performed in low humidity environments.
CQDs benefit from a size-tunable bandgap that allows absorption of photons with a relatively wide range of wavelengths, but a weaker absorption in the red and near-infrared (NIR) regions of the solar spectrum. Meanwhile, organic absorbers can have a narrower and more tunable spectral absorption than that of CQDs, making organic absorbers especially attractive for tandem solar cells, including with CQD absorbers. The opportunity exists to increase beyond the state-of-the-art PCE by tapping into the complementary spectral range of quantum-dot and organic absorbers and combining the two material types into hybrid tandem solar cells.
The first part of this talk will discuss our recent efforts aimed at fabricating highly efficient organic and CQD solar cells using large-area upscalable coating techniques. This effort has thus far yielded CQD solar cells with PCE > 10% and organic solar cells with PCE>11% using active layers coated in ambient air at high speed (>10 m/min). The second part of this talk will discuss the challenges and recent progress in the monolithic hybrid tandem integration of CQD and organic solar cells and the pathway toward achieving PCE>12%.