FULL PAPER Hybrid Solar Cells www.advtheorysimul.com Highly Efficient and Stable Solar Cells with Hybrid of Nanostructures and Bulk Heterojunction Organic Semiconductors Kiran Sreedhar Ram and Jai Singh* The power conversion efficiency (PCE) of a hybrid bulk hetero-junction organic solar cell with an active layer of a blend of PBDT TS1 (donor) and PCBM (acceptor) incorporated with copper zinc tin sulfide (CZTS) quantum dots (QDs) and zinc oxide (ZnO) nanowires is simulated. It is found that the incorporation of CZTS-QDs of a single radius (1.5 nm) enhances the PCE from 9.1% to 12.34% and of 13 different radii CZTS-QDs elevates PCE to 14.96%. This enhancement occurs mainly due to the enhancement in absorption that enhances short-circuit current density (J sc ) and fill factor (FF). Finally, a layer of ZnO nanowires is added on top of the glass to reduce the reflection losses and absorption of ultraviolet light in the active layer that causes degradation and reduces the stability of organic solar cells (OSCs). The hybrid structure, thus simulated, has an enhanced PCE of 16.32% and is expected to be relatively more stable. It is expected that the results of this simulation may inspire all researchers interested in the fabrication of highly efficient hybrid OSCs. 1. Introduction The research and development in the field of organic solar cells (OSCs) have shown huge improvement over recent years [1] be- cause OSCs are economical to fabricate through solution pro- cessing chemical technology. They are lightweight, flexible, and suitable for continuous bulk fabrication. In addition, the power conversion efficiency (PCE or ƞ) of OSCs have been progres- sively increasing and have recently reached more than 12%. [2–4] However, the researches in OSCs have to meet the following two very important challenges before their possible commercial use: 1) low PCE, only 12% in comparison with 25% of silicon solar cells; and 2) stability or the problem of degradation with pro- longed exposure to sunlight. Problem 1 is being tackled at present and gradually the PCE of OSCs is continuously improving. How- ever, problem 2 of stability is less rigorously studied. As most or- ganic materials degrade with long exposure to solar radiation, [5] K. S. Ram, Prof. J. Singh College of Engineering, IT and Environment Charles Darwin University Ellengowan Dr, Casuarina, NT 0810, Australia E-mail: jai.singh@cdu.edu.au The ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/adts.201900030 DOI: 10.1002/adts.201900030 the only possible solution appears to be the use of hybrid structure with inorganic materials. One of the ways of improving the PCE of OSCs is by enhancing the absorption of solar radiation in the organic active layer. For enhancing the absorption of pho- tons near the absorption edge of materi- als, quantum dots (QDs) have been used which enhance the absorption at higher wavelengths of the solar radiation. [6] How- ever, as the organic materials have nar- row bands, the absorption can be enhanced further by using QDs of multiple sizes. The research on organic–inorganic het- erojunction solar cells started in the last decade. These types of solar cells mainly use inorganic quantum dots as donors and or- ganic materials as acceptors. For example, by using antimony sulfide (Sb 2 S 3 ) quantum dots as donor material and poly(3-hexylthiopene-2,5-diyl) (P3HT) as acceptor polymer, a PCE of 5.13% has been achieved. [7] According to Rajesh et.al., [8] QDs of copper zinc tin sulfide (CZTS) being non-toxic can effectively replace the use of toxic chalcogenide quantum dots such as copper indium gallium selenide (CIGS) and cadmium telluride (CdTe). In addition to being non-toxic in nature, CZTS has abundant availabil- ity and the QD’s size, surface properties, and phase composi- tion at quantum level can be easily controlled by wet chemical synthesis. [8] In this paper, we have simulated the PCE of a bulk het- erojunction (BHJ) organic solar cell with a blend of PBDT- TS1 (donor) (polymer based on benzo[1,2-b:4,5-b ′ ] dithiophene (BDT) with a conjugated side chain consisting of 2-alkylthienyl) and [6,6]-phenyl-C 61 -butyric acid methyl ester (PCBM) (accep- tor) forming the active layer and found it to be 9.1%. Then, we have incorporated CZTS quantum dots of single and mul- tiple sizes into the organic active layer and calculated the re- sulting PCE to be 12.34% and 15.93%, respectively. Finally, we have added a layer of zinc oxide (ZnO) nanowires on the top of glass, which can absorb ultraviolet (UV) light and hence re- duce degradation of the active layer and enhance the lifetime of such OSCs. As the introduction of ZnO nanowires into PBDT- TS1/PCBM BHJ-OSC reduces reflection loss as well, the final PCE of this hybrid BHJ OSC boosted to 16.32%. It is expected that the results of this work may be useful to all researchers in the field. Adv. Theory Simul. 2019, 1900030 C  2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 1900030 (1 of 9)