Afshin Hadipour

Work functions of gold and silver are varied by over 1.4 and 1.7 eV, respectively, by using self-assembled monolayers. Using these modified electrodes, the hole current in a poly(2-methoxy-5-(2′-ethylhexyloxy)–1,4-phenylene vinylene) light-emitting diode is tuned by more than six orders of magnitude (see Figure). Suppression of the hole current enables measurement of the electron current in a polymer/polymer blend photovoltaic cell.

Abstract A solution‐processed polymer tandem cell fabricated by stacking two single cells in series is demonstrated. The two bulk‐heterojunction subcells have complementary absorption maxima at λ max ∼ 850 nm and λ max ∼ 550 nm, respectively. A composite middle electrode is applied that serves both as a charge‐recombination center and as a protecting layer for the first cell during spin‐coating of the second cell. The subcells are electronically coupled in series, which leads to a high open‐circuit voltage of 1.4 V, equal to the sum of each subcell. The layer thickness of the first (bottom) cell is tuned to maximize the optical absorption of the second (top) cell. The performance of the tandem cell is presently limited by the relatively low photocurrent generation in the small‐bandgap polymer of the top cell. The combination of our tandem architecture with more efficient small‐bandgap materials will enable the realization of highly efficient organic solar cells in the near future.

All-inkjet printed large area organic solar cells deposited from environmentally friendly solvents are demonstrated for the first time.

Abstract The emerging field of stacked layers (double‐ and even multi‐layers) in organic photovoltaic cells is reviewed. Owing to the limited absorption width of organic molecules and polymers, only a small fraction of the solar flux can be harvested by a single‐layer bulk heterojunction photovoltaic cell. Furthermore, the low charge‐carrier mobilities of most organic materials limit the thickness of the active layer. Consequently, only part of the intensity of the incident light at the absorption maximum is absorbed. A tandem or multi‐junction solar cell, consisting of multiple layers each with their specific absorption maximum and width, can overcome these limitations and can cover a larger part of the solar flux. In addition, tandem or multi‐junction solar cells offer the distinct advantage that photon energy is used more efficiently, because the voltage at which charges are collected in each sub‐cell is closer to the energy of the photons absorbed in that cell. Recent developments in both small‐molecule and polymeric photovoltaic cells are discussed, and examples of photovoltaic architectures, geometries, and materials combinations that result in tandem and multi‐junction solar cells are presented.

The use of an ITO-free MoO3/Ag/MoO3 anode to control the photon harvesting in PCDTBT:PC70BM solar cells is proposed. At first sight, the fact that these anodes possess reduced far-field transmission compared to ITO may seem to be a disadvantage. But, despite this, we show that by carefully tuning the resonant optical cavity we can enhance the external quantum efficiency close to the band edge of PCDTBT, resulting in high photocurrent and power conversion efficiency on par with ITO.