Efficient Quantum Dot Infrared Photovoltaic with Enhanced Charge Extraction via Applying Gradient Electron Transport Layers

Abstract PbS quantum dot (QD) infrared (IR) solar cells that can absorb low‐energy photons are promising photovoltaic devices to improve utilization of sunlight energy by broadening absorption range of the sunlight spectrum to short‐wave infrared region. For PbS QD photovoltaics, depleted heterojunction established between photoactive layer and ZnO electron transport layer (ETL) is critical to determine the performance of devices. However, undesired defects in ZnO films and mismatched energy levels have limited the improvement of device properties. Herein, a novel and simple gradient ZnO ETL is developed for achieving high‐performance QD IR solar cells by depositing a Cs‐doped ZnO thin layer on the pristine ZnO film. The resulting gradient ETL exhibits significantly suppressive trap states and a much smoother surface, efficiently reducing the trap‐assisted nonradiative recombination at the interfaces. Meanwhile, realigned energy levels of the gradient ZnO ETL facilitate the transport and extraction of photogenerated carriers. As a result, the champion device shows a high IR open circuit voltage (V_OC) of 0.446 V and IR power conversion efficiency (PCE) of 1.27% under 1100 nm filtered illumination. The V_OC and PCE are 0.507 V and 11.04% under AM1.5 illumination, respectively. These results demonstrate a promising strategy for exploiting high‐performance infrared optoelectronic devices.