Improved photovoltaic performance and device stability of planar heterojunction perovskite solar cells using TiO2 and TiO2 mixed with AgInS2 quantum dots as dual electron transport layers

Abstract Dual electron transport layers of TiO2 and TiO2 mixed with AgInS2 quantum dots (TiO2:AgInS2 QDs) were used for planar heterojunction perovskite solar cells (PSCs). The addition of AgInS2 into TiO2 induced a reduction of pinholes at the interspace of the grains of the TiO2. The PL intensity of the perovskite film deposited on TiO2/TiO2:AgInS2 QDs was quenched by the addition of AgInS2 QDs into TiO2. A rectification ratio (RR) of the planar PSCs was improved by using TiO2/TiO2:AgInS2 QDs as dual electron transport layers. As a result, fill factor (FF) and power conversion efficiency (PCE) of the device with TiO2/TiO2:AgInS2 QDs (1.6 mg mL−1) increased up to 0.77 and 17.5% as compared with FF (0.73) and PCE (16.3%) of the device with TiO2 single layer. The device with TiO2/TiO2:AgInS2 QDs as dual electron transport layers showed the improvement of the external quantum efficiency in the wavelength region from 300 nm to 750 nm as compared with that of the device with TiO2 single layer. This result is probably caused by the enhancement of light harvesting by AgInS2 QDs and the enhancement of the charge transfer from the perovskite layer to the dual electron transport layers. The long-term stability of the PSC with the dual electron transport layers was confirmed when 1.6 mg mL−1 of AgInS2 was added, followed by the encapsulation and improvement of the retained PCE (after storing the device in air for 15 days), from 11% to 34%, as observed. As has been indicated, the TiO2/TiO2:AgInS2 QDs as dual electron transport layers not only brought about improvement of photovoltaic performance but also enhanced its durability against photodegradation.