No abstract

For any emerging photovoltaic technology to become commercially relevant, both its power conversion efficiency and photostability are key parameters to be fulfilled. Colloidal quantum dot solar cells are a solution-processed, low-cost technology that has reached efficiency about 9% by judiciously controlling the surface of the quantum dots to enable surface passivation and tune energy levels. However, the role of quantum dot's surface on the stability of these solar cells has remained elusive. Here we report on highly efficient and photostable quantum dot solar cells with efficiencies of 9.6% (and independently certificated values of 8.7%). As a result of optimised surface passivation and suppression of hydroxyl ligands-which are found to be detrimental for both efficiency and photostability-the efficiency remains within 80% after

Colloidal Quantum Dot (CQD) light emitting diodes (LEDs) have delivered compelling performance in the visible, yet infrared CQD LEDs underperform their visible-emitting counterparts, largely due to their low photoluminescence quantum efficiency (PLQE). Herein, we employ a ternary blend of CQD thin film comprising a binary host matrix that serves to electronically passivate as well as to cater for efficient and balanced carrier supply to the emitting QD species. In doing so, we report on infrared PbS CQD LEDs with external quantum efficiency of ~7.9% and power conversion efficiency of ~9.3%, thanks to their very low trap-state density on the order of 10 14 cm-3 and very high PLQE in electrically conductive QD solids of more than 60%. When these blend devices operate as solar cells they deliver VOC approaching their radiative limit thanks to the synergistic effect of reduced trap state density and the density of states modification in the nanocomposite. Near and shortwave infrared (NIR, SWIR) light emitting diodes serve a rather broad range of applications, including night vision 1 , surveillance 2 , remote sensing 3 , biological imaging 4 and spectroscopy 5. Recent progress in on-chip and wearable infrared spectroscopy for quality inspection, health and process monitoring also requires the development of highly efficient,

Colloidal quantum dots have emerged as a material platform for low-cost high-performance optoelectronics. At the heart of optoelectronic devices lies the formation of a junction, which requires the intimate contact of n-type and p-type semiconductors. Doping in bulk semiconductors has been largely deployed for many decades, yet electronically active doping in quantum dots has remained a challenge and the demonstration of robust functional optoelectronic devices had thus far been elusive. Here we report an optoelectronic device, a quantum dot homojunction solar cell, based on heterovalent cation substitution. We used PbS quantum dots as a reference material, which is a p-type semiconductor, and we employed Bi-doping to transform it into an n-type semiconductor. We then combined the two layers into a homojunction device operating as a solar cell robustly under ambient air conditions with power conversion efficiency of 2.7%.

Developing low-cost photovoltaic absorbers that can harvest the short-wave infrared (SWIR) part of the solar spectrum, which remains unharnessed by current Si-based and perovskite photovoltaic technologies, is a prerequisite for making high-efficiency, low-cost tandem solar cells. Here, infrared PbS colloidal quantum dot (CQD) solar cells employing a hybrid inorganic-organic ligand exchange process that results in an external quantum efficiency of 80% at 1.35 µm are reported, leading to a short-circuit current density of 34 mA cm and a power conversion efficiency (PCE) up to 7.9%, which is a current record for SWIR CQD solar cells. When this cell is placed at the back of an MAPbI perovskite film, it delivers an extra 3.3% PCE by harnessing light beyond 750 nm.