Efficient Hybrid Tandem Solar Cells Based on Optical Reinforcement of Colloidal Quantum Dots with Organic Bulk Heterojunctions

While colloidal quantum dot photovoltaic devices (CQDPVs) can achieve a power conversion efficiency (PCE) of approximate to 12%, their insufficient optical absorption in the near-infrared (NIR) regime impairs efficient utilization of the full spectrum of visible light. Here, high-efficiency, solution-processed, hybrid series, tandem photovoltaic devices are developed featuring CQDs and organic bulk heterojunction (BHJ) photoactive materials for front- and back-cells, respectively. The organic BHJ back-cell efficiently harvests the transmitted NIR photons from the CQD front-cell, which reinforces the photon-to-current conversion at 350-1000 nm wavelengths. Optimizing the short-circuit current density balance of each sub-cell and creating a near ideal series connection using an intermediate layer achieve a PCE (12.82%) that is superior to that of each single-junction device (11.17% and 11.02% for the CQD and organic BHJ device, respectively). Notably, the PCE of the hybrid tandem device is the highest among the reported CQDPVs, including single-junction devices and tandem devices. The hybrid tandem device also exhibits almost negligible degradation after air storage for 3 months. This study suggests a potential route to improve the performance of CQDPVs by proper hybridization with NIR-absorbing photoactive materials.