Multi‐Bandgap Quantum Dots Ensemble for Near‐Infrared Photovoltaics

Abstract

Narrow bandgap quantum dots (QDs) are an important class of materials for near‐infrared (NIR) optoelectronic devices owing to their size‐tunable bandgap and chemical root processing. In photovoltaic applications, NIR QDs could be particularly useful to complement the sub‐bandgap transmission loss of NIR solar radiation from perovskite and c‐Si solar cells. However, insufficient carrier extraction thickness associated with the narrow NIR excitonic bandwidth of QDs limits the conversion efficacy of the broad NIR solar spectrum. Here, we utilize a multi‐bandgap QD ensemble which widens the NIR absorption bandwidth to mimic the broad solar spectrum. A solution‐phase ligand passivation strategy is used to control doping properties and energy level alignment of multi‐bandgap QDs. We successfully developed bulk‐heterojunction solar cells using the multi‐bandgap QD ensemble, which yields higher carrier extraction thickness and broader NIR absorption. The gain from NIR absorption and carrier transport resulted in higher short‐circuit current generation and power conversion efficiency (PCE) in solar cell devices. The champion device shows 8.73% PCE under 1.5 AM solar illumination and 7.44% and 5.05% PCE for the NIR photons transmitted from perovskite and c‐Si layers.