Influence of an Inorganic Interlayer on Exciton Separation in Hybrid Solar Cells.

Claire L Armstrong,Neil C Greenham,David Muñoz-Rojas,Marcus L Böhm,Mojtaba Abdi-Jalebi,Michael B Price,Judith L Macmanus-Driscoll,Nathaniel J K L Davis,Richard H Friend,Kevin P Musselman

doi:10.1021/acsnano.5b05934

Claire L Armstrong, Neil C Greenham + Show 8 more

Open Access

https://doi.org/10.1021/acsnano.5b05934

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Journal: ACS nano	Publication Date: Nov 10, 2015
Citations: 24	License type: cc-by

Affiliation: University of Cambridge, University of Waterloo

Abstract

It has been shown that in hybrid polymer–inorganic photovoltaic devices not all the photogenerated excitons dissociate at the interface immediately, but can instead exist temporarily as bound charge pairs (BCPs). Many of these BCPs do not contribute to the photocurrent, as their long lifetime as a bound species promotes various charge carrier recombination channels. Fast and efficient dissociation of BCPs is therefore considered a key challenge in improving the performance of polymer–inorganic cells. Here we investigate the influence of an inorganic energy cascading Nb2O5 interlayer on the charge carrier recombination channels in poly(3-hexylthiophene-2,5-diyl) (P3HT)–TiO2 and PbSe colloidal quantum dot–TiO2 photovoltaic devices. We demonstrate that the additional Nb2O5 film leads to a suppression of BCP formation at the heterojunction of the P3HT cells and also a reduction in the nongeminate recombination mechanisms in both types of cells. Furthermore, we provide evidence that the reduction in nongeminate recombination in the P3HT–TiO2 devices is due in part to the passivation of deep midgap trap states in the TiO2, which prevents trap-assisted Shockley–Read–Hall recombination. Consequently a significant increase in both the open-circuit voltage and the short-circuit current was achieved, in particular for P3HT-based solar cells, where the power conversion efficiency increased by 39%.

Highlights

Over the past decade there has been extensive research into organic/ inorganic hybrid solar cells as a low-cost and scalable photovoltaic technology.1À5 For a polymerÀmetal oxide hybrid solar cell, for example, the flexibility and high absorption coefficient of the polymer are combined with the stability, carrier mobility, and band gap tunability of the metal oxide
Employing X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) to characterize the TiO2 and Nb2O5 films, we identify polycrystalline TiO2 films consisting of the anatase phase
We have investigated the charge recombination mechanisms in P3HTÀTiO2 hybrid solar cells and PbSe CQDÀTiO2 photovoltaic devices when an energy cascading interlayer of Nb2O5 is introduced

Summary

Introduction

Over the past decade there has been extensive research into organic/ inorganic hybrid solar cells as a low-cost and scalable photovoltaic technology.1À5 For a polymerÀmetal oxide hybrid solar cell, for example, the flexibility and high absorption coefficient of the polymer are combined with the stability, carrier mobility, and band gap tunability of the metal oxide. To investigate whether similar arguments can explain the apparent difference in device performance between the P3HT- and PbSe CQD-based solar cells, we first study the nongeminate recombination dynamics of both device structures by following the transient photovoltage (TPV) decay under constant white light background illumination (see Figure 3).

Results

Conclusion