Manipulating Depletion Region of Aqueous‐Processed Nanocrystals Solar Cells with Widened Fermi Level Offset

• Published in: Small (Weinheim an der Bergstrasse, Germany) Vol. 14; no. 47; pp. e1803072 - n/a
• Main Authors: Wang, Lijing, Chen, Nannan, Jin, Gan, Feng, Tanglue, Du, Xiaohang, Liu, Fangyuan, Sun, Henan, Yang, Bai, Sun, Haizhu
• Format: Journal Article
• Language: English
• Published: Germany Wiley Subscription Services, Inc 01.11.2018
• Subjects: aqueous‐processed solar cells; bulk heterojunction; Circuits; Depletion; depletion region; Electron transport; Energy conversion efficiency; Fermi level; Fermi level offset; MA‐capped CdxZn1–xTe; Nanocrystals; Nanotechnology; Open circuit voltage; Photoelectricity; Photovoltaic cells; Silicon; Solar cells; Thickness ratio; MA-capped CdxZn1-xTe; bulk heterojunction; Fermi level offset; aqueous-processed solar cells; depletion region
• ISSN: 1613-6810; 1613-6829
• DOI: 10.1002/smll.201803072

Water soluble nanocrystals (NCs) are promising materials in aqueous‐processed solar cells because of their high extinction coefficient, low‐cost, and favorable photoelectric characteristics. However, the power conversion efficiency (PCE) of the present aqueous‐processed NC solar cells is restricted by the short depletion region of the active layer and limited Fermi level offset between NCs and the electron transport layer. Herein, these issues are effectively addressed by preparing CdxZn1–xTe NCs capped with 2‐aminoethanethiol hydrochloride. The introduction of Zn2+ into CdTe NCs widens the Fermi level offset from 0.68 to 0.74 eV, lengthens the depletion region from 130 to 137 nm, and hence brings obvious improvement in the open circuit voltage (Voc) and fill factor. Especially, the depletion region is successfully tuned from 137 to 171 nm, and even lengthened to a record thickness of 200 nm based on aqueous‐processed solar cells. As a result, a champion thickness ratio (74%) of depletion region to active layer (200/270 nm) is achieved. A champion PCE of 5.96% and short‐circuit current (Jsc) of 21.2 mA cm−2 are achieved among aqueous‐processed NC solar cells. This work provides a simple way to prepare polynary NCs and highlights a prospective method to develop more efficient and cost‐effective solution‐processed environment friendly solar cells. CdxZn1–xTe nanocrystals (NCs) are prepared and successfully applied to aqueous‐processed NC solar cells. The depletion region is continuously tuned from 130, 137, 171 to a champion thickness of 200 nm. The highest thickness ratio (74%) of depletion region to the active layer, the record power conversion efficiency (5.96%), and short‐circuit current (21.2 mA cm−2) are achieved among aqueous‐processed NC solar cells.