Efficient Hybrid Tandem Solar Cells Based on Optical Reinforcement of Colloidal Quantum Dots with Organic Bulk Heterojunctions

Abstract

While colloidal quantum dot photovoltaic devices (CQDPVs) can achieve a power conversion efficiency (PCE) of ≈12%, their insufficient optical absorption in the near‐infrared (NIR) regime impairs efficient utilization of the full spectrum of visible light. Here, high‐efficiency, solution‐processed, hybrid series, tandem photovoltaic devices are developed featuring CQDs and organic bulk heterojunction (BHJ) photoactive materials for front‐ and back‐cells, respectively. The organic BHJ back‐cell efficiently harvests the transmitted NIR photons from the CQD front‐cell, which reinforces the photon‐to‐current conversion at 350–1000 nm wavelengths. Optimizing the short‐circuit current density balance of each sub‐cell and creating a near ideal series connection using an intermediate layer achieve a PCE (12.82%) that is superior to that of each single‐junction device (11.17% and 11.02% for the CQD and organic BHJ device, respectively). Notably, the PCE of the hybrid tandem device is the highest among the reported CQDPVs, including single‐junction devices and tandem devices. The hybrid tandem device also exhibits almost negligible degradation after air storage for 3 months. This study suggests a potential route to improve the performance of CQDPVs by proper hybridization with NIR‐absorbing photoactive materials.

Monolithic Organic/Colloidal Quantum Dot Hybrid Tandem Solar Cells via Buffer Engineering

“…[9] Several research groups have recently reported various types of CQD-based hybrid tandem solar cells (TSCs). [9][10][11][12][13][14][15][16][17] However, previously reported hybrid TSCs have limitations in improving the PCE. In the case of CQD/CQD-based TSCs, the intrinsic low V OC of CQD limits the PCE.…”

“…[15] CQD/organic hybrid TSCs have been proposed as a promising combination since organic solar cells exhibit high V OC and strong absorption. [16] In the conventional device configuration, the organic back cell harvests near-infrared (NIR) light transmitted from the CQD front cell. However, the CQD front cell has a lower bandgap compared to the organic back cell, leading to photocurrent losses in the organic back cell.…”

“…When CQD and PTB7‐Th:IEICO‐4F are used as front cell and back cell in the existing conventional structure, the matching current is relatively low due to the large photocurrent loss in the back cell, resulting from the strong light absorption of the thick CQD front cell (Figure S2, Supporting Information). [ 16 ] We therefore built a reverse structure using PTB7‐Th:IEICO‐4F and CQD as front cell and back cell, respectively (Figure 2a), and calculated the matching current depending on the thickness of each layer (Figure 2b). Note that we assumed perfect charge extraction for each cell to calculate the matching current density, the J SC value is therefore the theoretical maximum for each structure.…”

Design Strategy of Quantum Dot Thin‐Film Solar Cells

“…For example, Aqoma et al reported organic-PbS QD tandem solar cells showing 12% of power conversion efficiency (PCE) recently ( Figure 2b). [31] We organized recent tandem solar cell development in Table 1. [31][32][33][34][35][36][37][38]…”

Efficient PbS Quantum Dot Solar Cells with Both Mg-Doped ZnO Window Layer and ZnO Nanocrystal Interface Passivation Layer

“…PbS colloidal quantum dot (CQD) solar cells have been rapidly developed in recent years with a certified power conversion efficiency (PCE) up to 13% in an optimal device configuration [ 1 , 2 ]. Compared to traditional photovoltaic technology, PbS CQD solar cells show great potential applications in energy products in view of their low cost, low temperature, and simple solution processing techniques [ 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 ]. More importantly, the bandgap of PbS CQDs can be easily controlled by varying the size of the CQDs, which enables efficient harvesting of a broad light spectrum from the visible to infrared region.…”