Efficient quantum dot infrared solar cells with enhanced low-energy photon conversion via optical engineering

Infrared (IR) solar cells are promising devices for improving the power conversion efficiency (PCE) of conventional solar cells by expanding the utilization region of the sunlight spectrum to near-infrared range. IR solar cells based on colloidal quantum dots (QDs) have attracted extensive attention due to the widely tunable absorption spectrum controlled by dot size and the unique solution processibility. However, the trade-off in QD solar cells between light absorption and photo-generated carrier collection has limited the further improvement of PCE. Here, we present high-performance PbS QD IR solar cells resulting from the combination of boosted light absorption and optimized carrier extraction. By constructing an optical resonance cavity, the light absorption is significantly enhanced in the range of 1,150–1,300 nm at a relatively thin photoactive layer. Meanwhile, the thin photoactive layer facilitates efficient carrier extraction. Consequently, the PbS QD IR solar cells exhibit a highly efficient photoelectric conversion in the IR region, resulting in a high IR PCE of 1.3% which is comparable to the highest value of solution-processed IR solar cells based on PbSe QDs. These results demonstrate that constructing an optical resonance cavity is a reasonable strategy for effective conversion of photons in the devices aiming at light in a relatively narrow wavelength range, such as IR solar cells and narrow band photodetectors.