Research Article Enhanced Device Performance of Bulk Heterojunction (BHJ) HybridSolarCellsBasedonColloidalCdSeQuantumDots (QDs)viaOptimizedHexanoicAcid-AssistedWashingTreatment AlfianF.Madsuha , 1,2 AkhmadH.Yuwono , 1 NofrijonSofyan , 1 andMichaelKrueger 3 1 Department of Metallurgical and Materials Engineering, Universitas Indonesia, Depok, West Java 16424, Indonesia 2 Freiburg Materials Research Centre, University of Freiburg, Stefan-Meier Str. 21, 79104 Freiburg im Breisgau, Germany 3 Carl-von-Ossietzky University Oldenburg, Institute of Physics, Carl-von-Ossietzky Str. 9-11, 26129 Oldenburg, Germany Correspondence should be addressed to Akhmad H. Yuwono; ahyuwono@metal.ui.ac.id Received 31 December 2018; Accepted 13 February 2019; Published 1 April 2019 Academic Editor: Alessandro Martucci Copyright©2019AlfianF.Madsuhaetal.isisanopenaccessarticledistributedundertheCreativeCommonsAttributionLicense, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. As-synthesized colloidal quantum dots (QDs) are usually covered by an organic capping ligand. ese ligands provide colloidal stability by preventing QDs agglomeration. However, their inherent electrical insulation properties deliver a problem for hybrid solar cell application, disrupting charge transfer, and electron transport in conjugated polymer/QDs photoactive blends. erefore, a surface modification of QDs is crucial before QDs are integrated into solar cell fabrication. In this work, enhancement of power conversion efficiency (PCE) in bulk heterojunction (BHJ) hybrid solar cells based on hexadecylamine- (HDA-) capped CdSe quantum dots (QDs) has been achieved via a postsynthetic hexanoic acid washing treatment. e investigation of the surface modification was performed to find the optimum of washing time and their effect on solar cell devices performance. Variation of washing time between 16 and 30 min has been conducted, and an optimum washing time was found at 22 min, resulting in a high PCE of 2.81%. e efficiency enhancement indicates improved electron transport, contributing in an increased short-circuit current density of solar cell devices. 1.Introduction Bulk heterojunction (BHJ) solar cells based on organic- inorganic hybrid materials have been developed signifi- cantly due to the possibilities for low-cost fabrication of high-efficiency solar cells in flexible large-area devices [1]. In principle, they are analogous to organic solar cells (OSCs); the dissimilarity is that they utilized inorganic semicon- ductors such as quantum dots (QDs) as electron acceptors, while OSCs is still dominated by fullerene derivatives [2]. Various types of QDs, namely, TiO 2 , ZnO, CdS, CdSe, and PbS, have been utilized so far as electron acceptors [3]. In 1996, the first polymer QDs hybrid solar cells that use CdSe QDs as the acceptor was reported, achieving a PCE of about 0.1% [4]. It was observed that a resulted PCE of their device was attributed to low charge transport and electron transfer of CdSe QDs in the photoactive layer. Afterward, many works have been focused on addressing this problem, which includes controlling the blends nanomorphology and tuning dots into various shapes such as rods and tetrapods [5]. ese works have contributed to the significant enhance- ment in the solar cell devices performance, with a recent PCE reaching 4% [6]. One of the crucial keys of the QDs-based solar cell to be addressed carefully is the surface of QDs itself. e stability of colloidal CdSe QDs is helped by the existence of surface ligands such as stearic acid, trioctylphosphine (TOP), and hexadecylamine (HDA) [7]. e long aliphatic tails of li- gands provide steric stabilization and hydrophobic surface, hence hindering nanoparticle agglomeration [8, 9]. How- ever, at the same time, they also perform as an electrically insulating layer, which has undesirable properties for the photoactive layer in hybrid solar cells application. e ligand layer affects the percolation network by inhibiting charge Hindawi Advances in Materials Science and Engineering Volume 2019, Article ID 7516890, 6 pages https://doi.org/10.1155/2019/7516890