Modification of a ZnO cathode by doping it with a hydroxyl-containing derivative - giving a ZnO-C60 cathode - provides a fullerene-derivative-rich surface and enhanced electron conduction. Inverted polymer solar cells with the ZnO-C60 cathode display markedly improved power conversion efficiency compared to those with a pristine ZnO cathode, especially when the active layer includes the low-bandgap polymer PTB7-Th.

We present high efficiency and stable inverted PSCs (i-PSC) by employing sol-gel processed simultaneously doped ZnO by Indium and fullerene derivative (BisNPC60-OH) (denoted as InZnO-BisC60) film as cathode interlayer and PTB7-Th:PC71BM as the active layer (where PTB7-Th is a low bandgap polymer we proposed previously). This dual-doped ZnO, InZnO-BisC60, film shows dual and opposite gradient dopant concentration profiles, being rich in fullerene derivative at the cathode surface in contact with active layer and rich in In at the cathode surface in contact with the ITO surface. Such doping in ZnO not only gives improved surface conductivity by a factor of 270 (from 0.015 to 4.06 S cm−1) but also provides enhanced electron mobility by a factor of 132 (from 8.25*10−5 to 1.09*10−2 cm2 V−1 s−1). The resulting i-PSC exhibits the improved PCE 10.31% relative to that with ZnO without doping 8.25%. This PCE 10.31% is the best result among the reported values so far for single junction PSC.

We present a novel electron transport (ET) polymer composed of polyfluorene grafted with a K(+)-intercalated crown ether involving six oxygen atoms (PFCn6:K(+)) for bulk-heterojunction polymer solar cells (PSCs) with regioregular poly(3-hexylthiophene) (P3HT) as the donor and indene-C(60) bisadduct (ICBA) or indene-[6,6]-phenyl-C(61)-butyric acid methyl ester (IPCBM) as the acceptor in the active layer and with Al or Ca/Al as the cathode. A remarkable improvement in the power conversion efficiency (PCE) (measured in air) was observed upon insertion of this ET layer, which increased the PCE from 5.78 to 7.5% for a PSC with ICBA and Ca/Al (5.53 to 6.63% with IPCBM) and from 3.87 to 6.88% for a PSC with ICBA and Al (3.06 to 6.21% with IPCBM). This ET layer provides multiple functionalities: (1) it generates an optical interference effect for redistribution of light intensity as an optical spacer; (2) it blocks electron-hole recombination at the interface with the cathode; (3) it forms an interfacial dipole that promotes the vacuum level of the cathode metal; and (4) it enhances electron conduction, as evidenced by (1) the increase in total absorption of 1:1 w/w P3HT:ICBA by a factor of 1.3; (2) the reduction in the hole-only current density profile by a factor of 3.3 at 2.0 × 10(5) V/cm; (3) the decrease of 0.81 eV in the work function of Al from 4.28 to 3.47 eV, as determined by UV photoelectron spectroscopy; and (4) the decrease in the series resistance of PSCs with ICBA and Al by a factor of 4.5, as determined by the current-voltage characteristic under dark conditions; respectively. The PSC of 7.5% is the highest among the reported values for PSC systems with the simplest donor polymer, P3HT.

Polymer solar cells (PSCs) based on fullerene derivatives often require additives to optimize active layer morphology. Here, the novel additive 1‐naphthalenethiol (SH‐na) is proposed for processing the PSC active layer of PTB7:PC71BM. Spin‐casting with SH‐na as additive achieves a power conversion efficiency (PCE) of 7.3%, compared to 6.7% for preparations containing the conventional 1,8‐diiodooctane additive. Dipping of the active layer into a methanol solution of critical SH‐na concentration increases the PCE further to 8.75%. This is mainly due to an improved open‐circuit voltage (from 0.72 to 0.79 V) together with a high achieved fill factor of 0.70. The improved PCE is correlated to the morphology optimization according to measurements of grazing incidence small/wide‐angle X‐ray scattering, neutron reflectivity, atomic force microscopy, Fourier transform infrared spectroscopy, and X‐ray photoelectron spectroscopy. The integrated results suggest that the halogen‐free additive SH‐na can form hydrogen bonds with both PTB7 and PC71BM, resulting in substantially improved PTB7 crystallization and multi‐length‐scale PC71BM dispersion for appropriate aggregation and networks. The subsequent dipping treatment with SH‐na further modifies the active layer morphology for a more PC71BM‐enriched surface and better PC71BM networks in the bulk film for an optimized electron‐to‐hole mobility ratio of 2.04, hence resulting in improved device performance.

Cross-linked anode interlayers (X-QUPD or X-OTPD) with solvent-resistance provide electron blocking to reduce electron–hole recombination for improving PCE of invert type solution processed perovskite solar cells.