Photocurrent Enhancement in CsPbBr3–xClx-based Solar Cells with Embedded PbS Quantum Dots

Two-step photon upconversion solar cells (TPU-SCs) are solar cells that can harvest sub-bandgap photons aiming to achieve higher efficiency. Recent TPU-SCs have been realized using epitaxial growth of III-V semiconductors with the incorporation of quantum dots (QDs). In this work, we report an initial step to achieve all-perovskite-based TPU-SCs. We utilized CsPbBr3-xClx nanocrystals with x = 0 and x = 1.5 to create all-perovskite interface-based solar cells (APISCs). To avoid the anion exchange reaction at the interface, we incorporated PbS QDs. The PbS QDs are expected not only to prevent the reaction but also to enhance the intraband transition which is a crucial electronic transition in the TPU-SCs. We compared photocurrent enhancement characteristics of APISCs with different deposition cycles of PbS QDs, i.e. we fabricated two APISCs with a single and triple deposition of PbS QDs. The APISC with a single PbS QD deposition exhibits photocurrent reduction with additional sub-bandgap photoirradiation. This can be due to photoinduced trap states in the perovskites. In contrast, the APISC with triple PbS QD deposition provides an increasing photocurrent with additional sub-bandgap photoirradiation. We attribute this phenomenon to the density of quantized states that allow the intraband transitions and provide a stronger effect that can overcome the effects of the photoinduced trap states. Since this report is an initial step, we will certainly develop better APISCs in the future.