PbS/ZnO Heterojunction Colloidal Quantum Dot Photovoltaic Devices by a Room Temperature Air-Spray Method

Colloidal quantum-dot-based photovoltaic devices (CQDPVs) were fabricated at room temperature in air atmosphere via a spraying technique. Lead sulfide colloidal quantum dots (CQDs) were utilized for this process and various fabrication conditions such as the spraying pressure, types of ligand molecules, duration of ligand exchange, and the band-gap of the CQDs were investigated in order to optimize the device performance. The power conversion efficiency reached 4.00% ($V_{{\rm OC}}$ of 0.57 V, $J_{{\rm SC}}$ of 11.79 mA·cm⁻², and FF of 0.60) when ∼145 nm thick sprayed CQD layers were utilized; this value is comparable to that achieved with the conventional spin-coated devices. The generality of the conditions used for fabrication of the sprayed CQDPVs was demonstrated in the fabrication of various CQDs having different band-gaps (1.34–1.61 eV). This technique provides an avenue for the application of a high-throughput process for CQDPV fabrication. Because the materials used herein for device fabrication are not completely optimized, there is further scope for improving device performance.

I. Introduction

Colloidal quantum dots (CQDs) have emerged as a class of promising photoactive materials for next-generation solar cell applications. CQDs offer the advantages of being inexpensive and solution processable, while exhibiting unique features such as a tunable band-gap due to the quantum-size effect and multiple exciton generation [1], [2]. Recent advances in the chemistry of CQDs and elucidation of the physics of device operation have led to the achievement of a power conversion efficiency (PCE) of CQD-based photovoltaic devices (CQDPVs) of up to ∼9%, which is comparable to that of organic photovoltaic devices [3]– [5]. The solution processability and superior absorption of CQDPVs extending into the near infrared spectral region open up the possibility for the commercialization of these devices and their use as lightweight and portable power conversion devices [6], [7].