Combined optical and electrical modeling of polymer:fullerene bulk heterojunction solar cells

Abstract

Optical interference effects are important for the total absorption as well as the profile of the exciton generation rate in polymer:fullerene bulk heterojunction solar cells. For solar cells with an active layer of poly͓2-methoxy-5-͑3Ј ,7Ј-dimethyloctyloxy͒-1,4-phenylenevinylene͔ as electron donor and ͓6,6͔-phenyl C 61 butyric acid methyl ester as electron acceptor, the total exciton generation rate can be directly extracted from the saturated photocurrent. It is demonstrated that for solar cells with an active layer thickness smaller than 250 nm, a constant exciton generation profile, based on this extracted total rate, gives identical electrical characteristics as compared to exciton generation profiles from an optical model. For thicker cells interference effects have to be taken into account, since a uniform generation profile leads to an overestimation of recombination losses and space-charge formation.

Charge dissociation in polymer:fullerene bulk heterojunction solar cells with enhanced permittivity

“…2 As a result, the saturated photocurrent is a direct measure for the amount of photons absorbed in the blend. 6 Typically, the dissociation efficiency in poly͓2-methoxy-5-͑3Ј ,7Ј-dimethoxyloctyloxy͒-p-phenylene vinylene͔ ͑MDMO-PPV͒ and ͓6,6͔-phenyl C 61 -butyric acid methyl ester ͑PCBM͒ bulk heterojunction ͑BHJ͒ solar cells is only 60% at short circuit conditions, representing a major loss mechanism in these devices. 2,7 …”

Mobility dependent efficiencies of organic bulk heterojunction solar cells: Surface recombination and charge transfer state distribution

“…Note that Eq. ͑1͒ is often [6][7][8][9][10][11]14 written in the form p diss = k d / ͑k d + k f ͒, where the dissociation constant k d relates to k rec and 0 via k d = k rec n i 2 / 0 . However, using the form of Eq.…”

“…This exciton then ͑ii͒ has to diffuse to the interface between the donor and acceptor molecules where it is separated. A frequently used model [6][7][8][9][10][11] for the simulation of current/voltage curves of organic bulk heterojunction solar cells assumes that the dissociated exciton ͑iii͒ first creates a charge transfer state 12,13 at the interface, before ͑iv͒ the electron and hole are separated and ͑v͒ transported to their respective junctions. A feature very uncommon to the classical picture of inorganic solar cells results from the interplay between electric field dependent dissociation and nonradiative recombination of the charge transfer state as outlined in Ref.…”

Ultimate performance of polymer:fullerene bulk heterojunction tandem solar cells

“…In a later stage we extended this model to a combined optical and electrical model. 12 The combined optical and electrical calculations confirmed that the exact shape of the absorption profile in the solar cells is not very critical as long as the active layer thickness ͑ALT͒ does not exceed 250 nm. 12 As a result the estimation of a maximum efficiency of 11% for a single cell, done with a constant profile, is expected to be approximately correct.…”