Electron and Hole Transport Layers: Their Use in Inverted Bulk Heterojunction Polymer Solar Cells

Abstract

Bulk heterojunction polymer solar cells (BHJ PSCs) are very promising organic-based devices for low-cost solar energy conversion, compatible with roll-to-roll or general printing methods for mass production. Nevertheless, to date, many issues should still be addressed, one of these being the poor stability in ambient conditions. One elegant way to overcome such an issue is the so-called "inverted" BHJ PSC, a device geometry in which the charge collection is reverted in comparison with the standard geometry device, i.e., the electrons are collected by the bottom electrode and the holes by the top electrode (in contact with air). This reverted geometry allows one to use a high work function top metal electrode, like silver or gold (thus avoiding its fast oxidation and degradation), and eliminates the need of a polymeric hole transport layer, typically of an acidic nature, on top of the transparent metal oxide bottom electrode. Moreover, this geometry is fully compatible with standard roll-to-roll manufacturing in air and is less demanding for a good post-production encapsulation process. To date, the external power conversion efficiencies of the inverted devices are generally comparable to their standard analogues, once both the electron transport layer and the hole transport layer are fully optimized for the particular device. Here, the most recent results on this particular optimization process will be reviewed, and a general outlook regarding the inverted BHJ PSC will be depicted.

Copper(I) thiocyanate (CuSCN) as a hole-transport material for large-area opto/electronics

“…Efficient organic and hybrid photovoltaic cells can be manufactured utilizing the bulk heterojunction (BHJ) concept [118][119][120] illustrated in figure 9 [102]. In the standard geometry, photons enter the cell through a transparent anode electrode and reach the BHJ active layer, which is typically a nanostructured composite of two materials, the so-called donor and an acceptor.…”

Organic Semiconductors: Past, Present and Future

“…This special issue consists of 13 papers especially covering many important topics including seven reviews in the field of organic semiconductors; Organic Semiconductors [13,14], material fabrication and properties [15][16][17][18], OFET [19,20], Sensor [19], OLED [21,22], solar Cells [23,24], Transport Property [17], and Bio-organic electronics [25].…”

“…The charge transport properties of materials are critical to optimize organic electronic devices. The importance of charge transport layers in the development of inverted bulk heterojunction polymer solar cells is the focus of [24] and the intrinsic bulk electron-phonon interaction and the behavior of mobility in the coherent regime of many systems, such as naphthalene, rubrene, and pentacene, is the focus of [17]. Properties of materials that can be used organic semiconductors are reported in references [15][16][17][18].…”

“…The concept of bandgap science of organic semiconductor films for use in photovoltaic cells, charge control by doping and design of the built-in potential based on precisely-evaluated doping parameters is summarized in the manuscript [23]. The use of electron and hole transport layers in the inverted bulk heterojunction polymer solar cells is the goal of the article [24].…”

Inverted Organic Photovoltaic Cell with ZnO Nanorod Structure

“…[18][19][20] Currently, several solution-based fabrication processes have been demonstrated, and the diameter of several 10 nm can be produced by optimizing the fabrication conditions. [21][22][23] However, most research has focused on the fabrication process for ZnO nanorods and nanofibers, 24,25 and research on the influence of the ZnO seed layer on the structure of the ZnO nanorods that are produced has been limited. We used a conventional chemical bath deposition method using a ZnO sol-gel precursor solution, which has several advantages over other methods, such as a simple procedure and the ability to control the diameter and length of the nanorods.…”